THESIS THE EFFECT OF MULTIPLE STRESSORS ON KAUAʻI’S FOREST BIRDS: DEMOGRAPHY, HEALTH, AND TROPHIC CASCADES Submitted by Ashley Cozette Romero Graduate Degree Program in Ecology In partial fulfillment of the requirements for the Degree of Master of Science Colorado State University Fort Collins, Colorado Fall 2024 Masters Committee: Advisor: Liba Pejchar David Koons Sarah Hart Copyright by Ashley Cozette Romero 2024 All Rights Reserved ii ABSTRACT THE EFFECT OF MULTIPLE STRESSORS ON KAUAʻI’S FOREST BIRDS: DEMOGRAPHY, HEALTH, AND TROPHIC CASCADES Island ecosystems harbor unparalleled biodiversity, providing habitat for a disproportionate share of the world’s species relative to their area. Nevertheless, the vulnerability of islands to disturbances that result in negative consequences renders them among the most endangered environments. Bird populations on islands are particularly susceptible and often strongly affected by invasive species, habitat loss, climate change, and disease, all of which has resulted in widespread decline and extinction. In the Hawaiian Islands, native forest bird populations confront numerous threats, with the majority of remaining native bird populations classified as threatened, endangered, or teetering on the brink of extinction. To sustain and recover island bird populations, it is essential to understand the direct and indirect impacts of anthropogenic changes on forest bird populations, and to what degree each driver of change influences bird health, demographics, and habitat quality. The goals of this project were to quantify how various stressors influence the body condition and sex ratios of Kauaʻi’s forest birds, and to assess if primary and secondary forest regeneration processes that affect forest bird resource and habitat availability are influenced by invasive rodent control. To address these questions, I collected and analyzed three years of forest bird banding data in the Alakaʻi Wilderness Preserve on Kauaʻi’s Island (Hawaiʻi, U.S.A.) from 2021 to 2023. Birds were banded in and outside of areas that have been subject to intensive rodent control for iii the past 5-9 years. I focused on four focal species of birds, three native and one non-native, and collected data to assess the body condition and sex of these captured birds. Mixed effects models were used to determine whether body condition was significantly associated with rodent control intensity on a local and landscape scale, malarial infection status, mean temperature during the peak mosquito breeding season, frequency of extreme rain events, canopy density, and topographic wetness index (TWI). Similarly, I used general linear models to test if rodent control intensity, malarial infection status, or date of capture was associated with a higher or lower likelihood of encountering a female. I found that body condition was negatively associated with positive malarial status for all but one of the focal species, and higher average temperatures and TWI were negatively associated with body condition for all species. None of the predictor variables evaluated were strong predictors of the sex of captured birds. To evaluate the effects of rodent control on forest regeneration processes that sustain bird habitat in the Alakaʻi Wilderness Preserve, I examined whether rodent control was associated with changes in seed rain, fruiting density, and seedling emergence. Seed traps were established in February of 2023 and were checked periodically over a six-month period to obtain seed rain data from within and outside of areas of rodent control. Seeds collected from traps were identified to the lowest possible taxonomic level. During each visit to collect seed trap contents, the number of fruits on all fruiting plants within five meters of each seed rain trap was estimated. These estimates were used to calculate relative fruiting densities in treatment and reference plots. To examine seedling emergence, emergence plots in treatment and reference plots were cleared of all vegetation in July of 2022. I used Mixed Effects Models to compare seed rain, fruiting density, and seedling emergence between sites with and without rodent control and found no iv differences in seed rain, seedling emergence, or fruiting density within and outside of rodent control. My findings suggest that variables that are related to disease transmission may be more influential in predicting the health of forest birds than variables related to predation risk or food and resource availability. These findings also suggest that rodent control, at least at current levels of intensity, may not play a significant role in forest regeneration in Kauaʻi’s ʻAlakaʻi Plateau. Further research is needed to understand the effectiveness of rodent control in this system, but reducing the prevalence of avian malaria and mitigating climate change will be critical to alleviating sub-lethal effects on Kauaʻi’s forest birds. This study contributes to our understanding of the sometimes complex and synergistic effects of invasive predators, disease, forest structure, and climate on forest birds and the dynamics of insular ecosystems. My findings and approach could have implications for conservation and restoration in the many areas globally where rat invasion, climate change, and disease may interact to pose similar threats. v ACKNOWLEDGEMENTS Because this research was conducted on Indigenous ‘aina (land) stewarded by Kanaka Oʻiwi (Native Hawaiians) for many generations past and more to come, I would like to begin by stating that I am eternally grateful to the generations of Native Hawaiians whose knowledge systems are deep and forever connected to the islands. Next, I would like to express my utmost appreciation and gratitude for my advisor Dr. Liba Pejchar. I would like to thank her for taking a chance on me and giving me the opportunity to work on this project. I am incredibly appreciative of the mentorship, patience, consistent support, and guidance that I have received from Dr. Pejchar throughout my journey as a first- generation college student completing this degree. It is in large part of this support as to why I have grown so much and gained considerable confidence in my own skills and abilities as a scientist. I would also like to thank my committee members Dr. David Koons and Dr. Sarah Hart for their support and help in the formation and analysis of this project. I thank Dr. Lisa Crampton at Kauaʻi Forest Bird Recovery Project (KFBRP), Dr. Chris Lepczyk and. Dr. Jean Fantle-Lepczyk at Auburn University, Dr. Jeffery Foster at Northern Arizona University, and Dr. Lainie Berry at Birdlife Australia, for development of the grant which funded much of this project. Without all the time, resources, advice, and support that I received from these people; this project would not have been possible. A special thank you to Dr. Mari Reeves at USFWS for all the patience, one-on-one time, and guidance through statistical analyses and data interpretation which helped me grow my analytical skills as well as my confidence in them. I would also like to thank all the technicians, students, and staff at KFBRP for all their help with data collection, advice, and other assistance in and outside of the field. I would like to express the utmost gratitude and appreciation for those who also extended their vi friendship to me during my field seasons, and both supported me through the tough times and celebrated the good ones. This friendship was essential to my success during this time. I want to thank the faculty and my fellow graduate students in the Department of Fish, Wildlife, and Conservation Biology (FWCB) for the camaraderie and always creating an inclusive, inspiring, and fun environment to be a part of. Thank you to my lab mates Carolyn Coyle and Kathleen Urchek for being such amazing friends, providing a safe space for me, and making sure I took time for rest and self-care throughout this process. I’m so glad to have gone through this journey together and will miss getting to share space together. Thank you to my mother, Ileana Romero for encouraging me to pursue my education and giving me the space to do so in a way that was non-traditional but made sense for me. Thank you to those friends from back home who I consider family. Leinani Lozi, Julien Lozi, Madori Rumpungworn, Mo Souza, Jessica Jimenez, Heather Bartlett, Sean Prentiss, Kassandra Talamantez, Alexis Shultz, Koaʻe Wold-Brennon. I thank them for their endless friendship and confidence in me throughout all these years. Without them, I would not be who I am today. Last but far from least, I would like to thank Josué Rodriguez for being my biggest hype man. Thank you for always believing in me, making me laugh, supporting me, and reminding me that I can overcome any obstacle life throws at me. vii TABLE OF CONTENTS ABSTRACT ................................................................................................................................. ii ACKNOWLEDGEMENTS ............................................................................................................ v CHAPTER ONE - KAUAʻI’S FOREST BIRDS IN CRISIS: THE EFFECTS OF MULTIPLE STRESSORS ON BODY CONDITION AND DEMOGRAPHY ........................................................ 1 SUMMARY .............................................................................................................................. 1 INTRODUCTION ..................................................................................................................... 2 METHODS ............................................................................................................................... 6 RESULTS ............................................................................................................................... 12 DISCUSSION ......................................................................................................................... 13 LITERATURE CITED ............................................................................................................. 25 CHAPTER TWO - EVALUATING THE EFFECT OF INVASIVE RAT CONTROL ON HABITAT REGENERATION FOR KAUAʻI’S FOREST BIRDS ..................................................................... 35 SUMMARY ............................................................................................................................ 35 INTRODUCTION ................................................................................................................... 35 METHODS ............................................................................................................................. 37 DISCUSSION ......................................................................................................................... 42 LITERATURE CITED ............................................................................................................. 51 APPENDIX ................................................................................................................................ 55 1 CHAPTER ONE - KAUAʻI’S FOREST BIRDS IN CRISIS: THE EFFECTS OF MULTIPLE STRESSORS ON BODY CONDITION AND DEMOGRAPHY SUMMARY Island bird species are at high risk of extinction globally. Anthropogenic drivers of loss and decline include invasive species, disease, habitat loss, and climate change. Although population declines are frequently well-documented, it is less clear which stressors are operating alone or interacting to drive these declines. Identifying the relative importance of these stressors is critical to effective conservation interventions given limited funds and time. In this study, I examined six potential stressors that could have sub-lethal effects on the body condition and demography of four forest bird species on Kauaʻi Island, Hawaiʻi. I captured birds in mistnets in areas with and without invasive rodent control and collected data on body condition and sex. I then evaluated stressors such as rodent control intensity, avian malaria, climate variables (temperature and precipitation), and habitat quality (canopy density and topographic wetness). I found that topographic wetness and the average temperature during the mosquito breeding season prior to when the bird was caught were negatively associated with body condition for all but one bird species. Both topographic wetness and temperature during the mosquito breeding season can influence the transmission and infection rates of avian malaria. Rodent control, malarial infection, and date of capture were hypothesized to potentially influence sex ratios in forest bird populations. I tested if sex ratios of the focal species were influenced by these variables, however no stressors were good predictors of bird sex. These results suggest that climate change and disease may exacerbate non-lethal negative effects on forest birds. Mitigating the effects of climate change and reducing the transmission of avian malaria are likely to improve health and prevent further population loss of forest bird populations in Hawaiian forests. 2 INTRODUCTION Biodiversity on islands often exhibit unique and remarkable evolutionary patterns that contribute to high levels of endemism when compared to continental ecosystems (Fernández- Palacios et al. 2021). Yet, island flora and fauna has also declined rapidly over the last several centuries due to human activities (Russell and Kueffer 2019, Matthews et al. 2022). Bird populations on islands have been particularly vulnerable to these impacts and have suffered disproportionately high extinction rates (Karels et al. 2008). Birds provide essential ecosystem services to the ecology and health of island ecosystems such as seed dispersal, pollination, and pest management (Whelan et al. 2008, Şekercioğlu et al. 2012). Many Indigenous island cultures have unique and deep cultural ties to avian species (Westergaard 2022). Declines in bird population can lead to cascading and sometimes catastrophic effects for ecosystem function, biodiversity, biotic relationships, and biocultural history (Banko et al. 2001, Culliney et al. 2012, Kaushik et al. 2018). One of the most iconic examples of the effects of human disturbances on island birds is the case of Hawaiian avifauna (Paxton et al. 2022). Often referred to as “the extinction capital of the world”, Hawaiian forest birds have suffered numerous extinctions since human colonization. At least 95 of 142 known species have gone extinct since humans arrived on these islands, and at least 69% of the species that are still extant are federally listed as threatened or endangered (Banko et al. 2001, Gon and Winter 2019). Primary threats driving these extinctions and ongoing population declines include the introduction of invasive predators, disease, habitat loss and degradation, and climate change (Atkinson et al. 2013, Banko et al. 2019). These threats often interact to exacerbate threats to avian populations (Reed et al. 2012). Understanding which of these stressors are the primary driver of population declines, using early warning signs such as poor body condition and skewed sex ratios, could be critical to informing time and cost-effective conservation interventions. Bird body condition provides insight into the energetic state of an individual, has implications for the ability of an individual to persist in various environments (Schulte-Hostedde et al. 2005), and influences reproductive potential (Labocha and Hayes 2012). Body condition can reflect an individual's response to environmental conditions including habitat quality, presence of introduced predators, and climatic conditions (Benson and Bednarz 2010, Weterings https://paperpile.com/c/Iaa5rp/Iwg7f https://paperpile.com/c/Iaa5rp/Iwg7f https://paperpile.com/c/Iaa5rp/O613y+CHHoP https://paperpile.com/c/Iaa5rp/KOY9R https://paperpile.com/c/Iaa5rp/LLBey+hOg6J https://paperpile.com/c/Iaa5rp/fks8j https://paperpile.com/c/Iaa5rp/uUj0a+pFrH0+2cyQn https://paperpile.com/c/Iaa5rp/uUj0a+pFrH0+2cyQn https://paperpile.com/c/Iaa5rp/Db0TZ https://paperpile.com/c/Iaa5rp/uUj0a+caaX7 https://paperpile.com/c/Iaa5rp/kQlf+p5Tq https://paperpile.com/c/Iaa5rp/ICuS https://paperpile.com/c/Iaa5rp/N2sc https://paperpile.com/c/Iaa5rp/N2sc https://paperpile.com/c/Iaa5rp/SgMT https://paperpile.com/c/Iaa5rp/BTHr+IHdm+ordP 3 et al. 2022, McCloy and Grace 2023), and individuals with better body condition are more likely to have higher survival rates and reproductive success (Peig and Green 2010), and reduced susceptibility to disease (Catfolis et al. 2023). As such, measuring changes in body condition can provide a valuable indication of the benefits of conservation interventions (Lavers et al. 2010). In addition to body condition sex ratios can also be used to measure the response of forest bird populations to management interventions such as predator control or disease mitigation (Nadal et al. 2016). Sex ratios of small and declining species tend to be male-biased (Morrison et al. 2016). In most bird species females preferentially incubate nests with males providing nutritional assistance by feeding the incubating females (Bambini et al. 2019). Incubating individuals are at a greater risk of predation (Heinsohn et al. 2019), and the cost of reproduction is often more energetically demanding for females (Sibly et al. 2012). This may lead to an altered sex ratio in the overall population. Skewed sex ratios are important potential barriers to productivity in birds, and at already low population densities can further increase risk of extinction (Reidy et al. 2009, Morrison et al. 2016, Ancona et al. 2020). Of all stressors to island birds, the effects of invasive rodents have been particularly well documented. Rats and mice are directly or indirectly associated with species extinction and population decline (Courchamp et al. 2003, Witmer et al. 2014, Russel and Holmes 2015, Bellard et al. 2016). Invasive rodents can spread disease, compete with birds for resources, and degrade habitat through frugivory and herbivory (Doherty et al. 2016). Rats are one of the most effective predators of birds (Lavers et al. 2010) and because many rat species are arboreal, nesting females, young chicks, and eggs are especially vulnerable to depredation (Fontaine and Martin 2006, Reidy et al. 2009). This is particularly true on islands where birds have often evolved in the absence of rats, and any former adaptations to coexist with predators like rats have been lost (Moors et al. 1992). Black Rats are the most common rat species in Hawaiʻi (Shiels and Drake 2015) and have been implicated in population declines of native seabirds (Raine et al. 2020)) and forest birds (Harper and Bunbury 2015). This species was one of the primary drivers for the rapid decline of Oahu ‘Elepaio (Chasiempis ibidis) (Mosher et al. 2010) and is the cause of approximately 16% all passerine nest failures in Hawaiʻi’s wet montane forests (Pratt et al. 2009). Introduced pathogens are another major stressor for island birds, because these species lack a coevolved immunological response (Vanderwerf 2012). The introduction of the mosquito- https://paperpile.com/c/Iaa5rp/BTHr+IHdm+ordP https://paperpile.com/c/Iaa5rp/fVoD https://paperpile.com/c/Iaa5rp/RZEK https://paperpile.com/c/Iaa5rp/gc76 https://paperpile.com/c/Iaa5rp/x40d https://paperpile.com/c/Iaa5rp/X0Do https://paperpile.com/c/Iaa5rp/X0Do https://paperpile.com/c/Iaa5rp/OK1L https://paperpile.com/c/Iaa5rp/Q3vq https://paperpile.com/c/Iaa5rp/iUOE https://paperpile.com/c/Iaa5rp/yD2E+X0Do+m6EE https://paperpile.com/c/Iaa5rp/oUfz+feMo+izWm+5PdZ https://paperpile.com/c/Iaa5rp/oUfz+feMo+izWm+5PdZ https://paperpile.com/c/Iaa5rp/qct6 https://paperpile.com/c/Iaa5rp/gc76 https://paperpile.com/c/Iaa5rp/m6EE+XBot https://paperpile.com/c/Iaa5rp/m6EE+XBot https://paperpile.com/c/Iaa5rp/HBhQ https://paperpile.com/c/Iaa5rp/SKLH https://paperpile.com/c/Iaa5rp/SKLH https://paperpile.com/c/Iaa5rp/K8at https://paperpile.com/c/Iaa5rp/K8at https://paperpile.com/c/Iaa5rp/VFLS https://paperpile.com/c/Iaa5rp/fWrC https://paperpile.com/c/Iaa5rp/gFOe https://paperpile.com/c/Iaa5rp/gFOe https://paperpile.com/c/Iaa5rp/cCO8 4 transmitted parasite, avian malaria (Plasmodium relictum) to the Hawaiian Islands has had devastating consequences to avian populations and has fundamentally altered the distribution of native forest birds (Lapointe et al. 2012). Many native species have been extirpated from lower elevations where mosquito populations are high, and constrained to a smaller area of disease-free refuge in higher elevations where the climate is inhospitable for mosquitoes and most of the remaining intact and malaria-free native forest still exists (Samuel et al. 2015, Liao et al. 2017). Avian malaria, spread by the southern house mosquito (Culex quinquefasciatus), is associated with a 62-90% mortality rate in Hawaiian birds such as Hawaiʻi ʻAmakihi (Chlorodrepanis virens), ʻapapane (Himatione sanguinea), and iʻiwi (Drepanis coccinea) after a single mosquito bite. In the case of experimentally infected birds, the mortality rate can exceed 90% (Atkinson et al. 1995, 2000; Yorinks and Atkinson 2000). While there is growing evidence for increased tolerance in certain species (Atkinson et al. 2013, Samuel et al. 2015) most native birds face acute infection after exposure, often suffering from damage to internal organs, anemia, lethargy, anorexia, and lowered immune response (Atkinson et al. 1995, Lapointe et al. 2012). Environmental attributes such as climate and topography can also affect bird fitness and health (Remeš and Harmáčková 2018, Molina-Marin et al. 2022). Extreme temperatures can influence stress response, body size, nesting success, reproduction, and growth (Sauve et al. 2021, McCloy et al. 2023). Additionally, climate change is expected to exacerbate both the frequency and severity of extreme weather events. Even short-term extreme weather patterns can reduce food availability, add to energetic demands, and lead to death in birds with weakened immune systems (Lapointe et al. 2012, Soriano-Redondo et al. 2016, McCloy and Grace 2023). Climate may influence the distribution and prevalence of disease (Kalluri et al. 2007). Mosquitoes that spread disease, including avian malaria, have higher rates of reproduction, faster development, increased adult survival, and increased rates of disease transmission in warmer temperatures. Warming temperatures also mean the transmission of avian malaria at higher elevations, including in the last refuges for Hawaiian forest birds (Benning et al. 2002, Lapointe et al. 2012, Ciota et al. 2014). Habitat quality and forest structure can affect access to resources, refuge from predators and extreme weather, and the availability of suitable nesting areas. Topographic Wetness Index (TWI) and canopy density could be important predictors of habitat quality for birds in tropical forests. TWI is a measurement that describes how water pools in areas and has been shown to https://paperpile.com/c/Iaa5rp/xluH https://paperpile.com/c/Iaa5rp/GVUk+KOge https://paperpile.com/c/Iaa5rp/UX9i+Hg7w+ny3k https://paperpile.com/c/Iaa5rp/UX9i+Hg7w+ny3k https://paperpile.com/c/Iaa5rp/p5Tq+GVUk https://paperpile.com/c/Iaa5rp/ny3k+xluH https://paperpile.com/c/Iaa5rp/eOzV+cK9z https://paperpile.com/c/Iaa5rp/bdTd+hcVa https://paperpile.com/c/Iaa5rp/bdTd+hcVa https://paperpile.com/c/Iaa5rp/xluH+fBhJ+ordP https://paperpile.com/c/Iaa5rp/w9zO https://paperpile.com/c/Iaa5rp/TvFV+xluH+AdXP https://paperpile.com/c/Iaa5rp/TvFV+xluH+AdXP 5 capture patterns of soil moisture and water availability or utilization in an area (Dyer 2009). This water retention can play a major role in determining plant species distributions and community structure (Moeslund et al. 2013) which may have implications for food and habitat availability for forest birds (Økland et al. 2008, Ediriweera et al. 2016). Vegetation structure can also play a key role in predicting habitat quality for birds by influencing the availability of food resources and nest sites (Hinsley et al. 2006). Increased forest complexity has been associated with better body condition in birds because of greater food availability and better refuge against extreme climatic events (Scheffers et al. 2014, Catfolis et al. 2023). Fretz (Fretz 2002) found that a higher canopy density was related to greater food availability for Hawaiʻi akepa (Loxops coccineus), with both individual and population level consequences. The objective of this study was to evaluate the effect of multiple stressors on the body condition and demography of Kauaʻi’s forest birds. Focusing on four focal bird species on Kauaʻi’s Alakaʻi Plateau, I used banded birds to assess the relationship between rodent control intensity, malarial status, canopy density, topographic wetness index, temperature during the prior mosquito breeding season, and number of extreme precipitation events in the beginning of the forest bird breeding season, with forest bird body condition. I further tested for associations between the likelihood of a captured bird being a male or female with rodent control intensity, malarial status, and the date of capture. I hypothesized that the negative health effects associated with malarial infection would cause a positive malarial infection status to be negatively correlated with body condition. Additionally, I predicted that increased temperatures during the mosquito breeding season would increase mosquito abundance and malarial infection and would correlate negatively with body condition. A higher number of extreme precipitation events at the beginning of the breeding season was expected to increase energetic demands and stress response for birds, also leading to a negative correlation with body condition. Higher trap density was expected to reduce both predation and competition pressure on focal species leading to increased body condition. Increases in TWI, and canopy density were predicted to lead to higher food and habitat availability and therefore be positively correlated with body condition. I further hypothesized that a higher rat trap density would result in a higher probability of capturing a female due to decreased predation pressure on incubating females. Finally, I predicted that malarial infection and date of capture may be associated with the sex ratios of https://paperpile.com/c/Iaa5rp/dbHu https://paperpile.com/c/Iaa5rp/wjGu https://paperpile.com/c/Iaa5rp/nQr0+g9nL https://paperpile.com/c/Iaa5rp/3Ry9 https://paperpile.com/c/Iaa5rp/L1BM+RZEK https://paperpile.com/c/Iaa5rp/L1BM+RZEK https://paperpile.com/c/Iaa5rp/9YMT 6 captured birds. These predictions were based on findings from previous research that indicate malarial infection may affect sexes differentially, and that birds may have capture probabilities that differ according to behavior and life history characteristics that vary between sexes. The direction of these effects could be either positive or negative due to mixed findings from previous research and differences in behaviors in different species (Lachish et al. 2011, Ágh et al. 2019, García et al. 2023). The results of this study will help us better understand sub-lethal effects of multiple stressors on Kauaʻi’s forest birds and could be used to guide management actions in Hawaiʻi and other areas globally. METHODS Study Area This study was located on the island of Kauaʻi, Hawaiʻi (U.S.A.) in the eastern portion of Kauaʻi’s Alakaʻi plateau (22° 7’ 18’’ N and 159° 33’ 48’’ W) within the Alakaʻi Wilderness Preserve (Figure 1.1). This is the region where most of Kauaʻi’s native forest birds still persist because it includes the highest elevation terrain on the island, and the native plant community is relatively intact. This preserve, with an area of approximately 70 km2, is a wet montane forest and receives some of the heaviest rainfall in the world (>6,000 mm of rain per year). Bogs are present throughout the Alakaʻi but most of the region is well drained (Foster et al. 2004). The forest birds in this region have been managed and monitored by the Kauaʻi Forest Bird Recovery Project (KFBRP) since 2003. KFBRP is a collaborative project between the Hawaiʻi Division of Forestry and Wildlife (DOFAW) and the Pacific Studies Cooperative Unit of the University of Hawaiʻi. Two study sites, Halepaʻakai (22° 4’ 46” N and 159° 32’ 51” W) and Mohihi (22° 7’ 18” N and 159° 33’ 48” W) were selected within the plateau to conduct this study (Figure 1.1). Halepaʻakai (HPK) is at 1350 m in elevation and Mohihi (MOH) is at 1250 m, and both have been the focus of forest bird research and management by KFBRP over the past decade. A portion of each study site (HPK = 93ha; MOH = 56ha) has been subject to intensive rat control over the past 6-9 years to reduce rodent populations in critical habitat for Kauaʻi’s threatened and 7 endangered species. Hereafter, areas with and without rodent control will be referred to as treatment and reference areas respectively. HPK was fenced with all ungulates removed in 2017. MOH is not fenced and contains feral ungulates including deer (Axis axis) and pigs (Sus scrofa). The HPK trap grid has about 164 rat traps that have been operating continuously since March 2015 and MOH has been operating about 124 traps since fall 2018. Both HPK and MOH rat control grids contain Goodnature A24 rat traps (Figure 1.2, Appendix) in which traps are spaced approximately 100 x 50m apart depending on landscape and habitat. KFBRP staff checked the traps in both grids two to three times per year. Each time traps were visited the lure and CO2 cartridge was changed as needed to ensure traps remained operational. Relative rodent abundance in treatment and reference areas was monitored during the breeding season using tracking tunnels (Figure 1.3, Appendix). Presence or absence of rat footprints were used to quantify the proportion of tunnels where rat tracks were present relative to the total number of tunnels set. Using these track tunnel data as an index of relative rat abundance, previous studies in this study system have demonstrated lower rodent abundance in the treatment areas (Crampton et al. 2022). Study Species This study examined four focal forest bird species: Kauaʻi ʻAmakihi (Hemignathus stejnegeri), ʻAnianiau (Magumma parva), Kauaʻi ʻElepaio (Chasiempis sclateri), and Warbling white-eye (Zosterops japonicus). These species were chosen because they have relatively small home ranges and site fidelity (0.015 - 0.45ha; (Guest 1973, van Riper 1995, Tweed et al. 2003, Vanderwerf et al. 2013) relative to other species (e.g., ʻApapane (Himatione sanguinea)) that range widely to follow pulses in food availability (Smetzer et al., 202; Table 1.1, Appendix). Smaller home ranges decrease the probability that birds in rat-controlled areas are traveling to areas without rat control, and vice versa. Two of the focal species are Hawaiian Honeycreepers (Fringillidae: Carduelinae). Kauaʻi ʻAmakihi is a generalist that feeds on insects, nectar, and fruit. The ʻAnianiau (Magumma parva) is also a generalist that feeds on nectar from flowering plants and gleans adult and larval arthropods from trees, shrubs, vines, and fern fronds. The Kauaʻi ʻElepaio (Chasiempis sclateri), https://paperpile.com/c/Iaa5rp/lir3 https://paperpile.com/c/Iaa5rp/7TcI+CZ1m+DBOU+ZPa0 https://paperpile.com/c/Iaa5rp/7TcI+CZ1m+DBOU+ZPa0 8 is a native monarch flycatcher. This small brown bird feeds primarily on a wide range of arthropods from snags, the ground, logs, rock crevices, and virtually all parts of trees (Pratt et al. 2009). The only non-native species included in this study is the Warbling white-eye (Zosterops japonicus). This species is included because it is one of the most successful introduced species in Hawaiʻi and are abundant in the study region. The Warbling White-eye consumes arthropods, nectar, and fruit, and may compete with native birds for both habitat and food resources (Freed and Cann 2014). Mist Netting and Banding I used mist nets to capture, band, and collect data on body condition, sex, disease status, and other morphological characteristics of the focal species. Mist netting occurred intermittently from mid-March through August, which covers the primary breeding season for Hawaiian forest birds (Pratt et al. 2009). Mist netting occurred throughout the trapping and reference areas. A variety of banding locations were chosen throughout the Alakaʻi wilderness preserve. These locations were chosen to strategically target areas where bird capture would be the highest and that were also accessible given the challenging terrain, and to make use of data that were collected by other concurrent projects mistnetting birds in the study region (Figure 1.4, Appendix). Nets varied in size from 6-12m long and had mesh size of 30 mm. Mist nets were opened only under satisfactory weather conditions and closed in weather conditions that were not suitable according to best banding practice (IACUC protocol 08-585-13). Birds that were caught were fitted with a federal bird band with a unique identifying number and often color bands for identification and resighting. Mass, fat content, body/flight feather molt, and the length of the tarsus, culmen, and wing cord, were recorded when possible. Mass and morphometric measurements were used to assess body condition. A blood sample was taken to be used for malarial screening and sexing before the birds were released. Body Condition Body condition is often measured using indices calculated from measurements such as body fat, mass, and other morphometric measurements (Labocha and Hayes 2012, Barnett et al. 2015). Body mass is a morphometric measurement shown to be affected by predator removal programs and can be a reliable predictor of the benefit of removal (Lavers & Wilcox https://paperpile.com/c/Iaa5rp/gFOe https://paperpile.com/c/Iaa5rp/gFOe https://paperpile.com/c/Iaa5rp/2M5I https://paperpile.com/c/Iaa5rp/2M5I https://paperpile.com/c/Iaa5rp/gFOe https://paperpile.com/c/Iaa5rp/fVhS+SgMT https://paperpile.com/c/Iaa5rp/fVhS+SgMT 9 2010). Body mass is commonly used in combination with a linear body measurement such as tarsus length (Peig and Green 2010). Using methods from Peig & Green (Peig and Green 2009) body condition was assessed using the Scaled mass index (𝑀̂i). The scaled mass index uses a fixed value of a linear body measurement to standardize body mass. This is based on a scaling relationship between mass and length. The scaled mass index equation is as follows: Scaled mass index (𝑀̂i) = Mi [𝐿0𝐿𝑖 ]𝑏𝑆𝑀𝐴 In this equation Mi and Li are the body mass and linear body measurement of the individual i respectively. bSMA Is a scaling exponent estimated by the standardized major axis (SMA) regression of lnM on lnL. L0 is the arithmetic mean value for the study population, and Li is the predicted body mass for individual i when the linear body measurement is standardized to L0. A higher 𝑀̂i is indicative of better body condition (English et al. 2018). Covariates Sexing and Malarial Status After morphometric measurements were taken from captured birds, approximately 50 µL of blood was collected via brachial venipuncture in heparinized capillary tubes. Blood was then transferred to a lysis buffer to preserve the DNA. Once blood samples were taken out of the field, they were put on ice and shipped to Northern Arizona University (NAU) for molecular sexing and screening for malaria presence. Samples were returned with either a negative or positive malarial status and the sex of the birds. Rodent Control Intensity Because previous work in this system demonstrated that trapping decreases rodent abundance (Crampton et al. 2022), and directly measuring rat abundance across the entire study area was beyond the scope of this project, I used rat trap density as an index of rodent control intensity. This will be referred to as the “trap count” from here on forward. Rat control density was calculated as the number of rat traps located within 150 and 300 m from the location where a bird was caught. To evaluate the effects of rodent control, ArcGIS Pro (ESRI version 3.3.1, https://paperpile.com/c/Iaa5rp/fVoD https://paperpile.com/c/Iaa5rp/Ftvo https://paperpile.com/c/Iaa5rp/VmXF 10 Redmond WA) was used to summarize the number of rat traps within an 150m and 300m radius from where the bird was caught. These distances were selected because they capture the average home range sizes of the focal study species, which range from approximately 0.015 ha - 0.45ha (Guest 1973, van Riper 1995, Tweed et al. 2003, Vanderwerf et al. 2013). Topographic Variables To assess whether topographic variables influence body condition, I acquired high resolution (1m2) LiDAR imagery for the Alakaʻi Plateau which was taken in 2017 (Fricker et al. 2021). From this imagery, I derived two habitat metrics, which were canopy density and topographic wetness index (TWI). Using ArcGIS Pro (ESRI version 3.3.0, Redmond WA), I summarized TWI and canopy density as the average TWI and canopy density within 150m and 300m from the bird's capture point. Climatic Variables To evaluate effects of climate on bird body condition, I obtained daily precipitation and temperature values from a National Oceanic and Atmospheric Administration weather station, made publicly available on https://www.noaa.gov/. I used the Lihue Weather Service Office Station (Network ID: GHCND:USW00022536). To obtain the average temperature during the mosquito breeding season, I summarized the average temperature throughout the peak months of the mosquito breeding season for Hawaiʻi which lasts from July through November (Lapointe et al. 2012, Samuel et al. 2015, Maldinich, personal communication). For precipitation events, I used the daily precipitation values for 10 years prior to the end of this study (2013–2023). Using this information, I calculated the 90th percentile threshold of the daily precipitation values for that 10-year period (Post et al. 2021). Then I found the number of days exceeding this threshold, and summarized the number of extreme weather events that occurred within the first three months of the year when the bird was caught. These months were chosen because these are the months just prior to, and at the beginning of the breeding season where birds are generally gathering energy stores and preparing to reproduce. https://paperpile.com/c/Iaa5rp/d4k9 https://paperpile.com/c/Iaa5rp/d4k9 https://www.noaa.gov/ https://paperpile.com/c/Iaa5rp/xluH+GVUk https://paperpile.com/c/Iaa5rp/xluH+GVUk https://paperpile.com/c/Iaa5rp/xluH+GVUk https://paperpile.com/c/Iaa5rp/xluH+GVUk https://paperpile.com/c/Iaa5rp/xluH+GVUk https://paperpile.com/c/Iaa5rp/3n9C 11 Data Analysis I employed generalized linear mixed models (GLMM) to determine if body condition was associated with any of the stressor variables of interest. Specifically, I used body condition score as the response variable with trap count, sex (male or female), malarial status (positive or negative), average Topographic Wetness Index (TWI), average canopy density, number of extreme precipitation events, and the mean temperature throughout the previous year’s mosquito breeding season as explanatory fixed effects. The bird's federal band identification number was added as a random effect to account for individual variability and for recaptured birds. To evaluate the relationship between stressors and sex ratios, I used a binomial logit- linked general linear model (GLM) sex (male or female) as the response variable. For this analysis I only included fixed effects that were thought to possibly influence sex composition in forest birds. The fixed effects included in the analysis were trap count, malarial status, and julian date when the bird was captured. For the sex analysis, only data from the latest date of capture was used for any recaptured birds throughout the season so all data points were from unique individual birds. A list of possible models was constructed using a knowledge driven approach. Prior knowledge of the system and literature were used to construct combinations of stressors that were thought to possibly influence the body condition or sex ratio of our focal species. Models were fit using the lme4 package in RStudio version 4.3.2 (R Core Team 2023). A correlation matrix was run to assess collinearity between explanatory variables and variables with high collinearity were not included in the same model. Variables summarized at 150m and 300m (trap count, TWI, canopy density) were tested at both scales in different models. No models included the same variable tested at both scales due to spatial autocorrelation, and top models were examined at each of the two intervals. Akaike's information criteria adjusted for small sample size (Burnham and Anderson 2013) was used to assess the fit of the model and all models were ranked using ΔAICc. The regression coefficients were examined to determine the strength and direction of the relationship between body condition and covariates. Any models with ΔAICc ≤ 2 were considered as alternative models that were equivalent to the top model. https://paperpile.com/c/Iaa5rp/hUto 12 RESULTS I caught 681 birds of the four focal species across the duration of the study. These represent 604 individual birds because 61 birds were recaptured at least once. Of these 681 bird captures, 399 of them resulted in sufficient data to conduct the body condition analysis. The models thus incorporate data from 74 Kauaʻi ʻAmakihi captures, 49 ʻAnianiau, 115 Kauaʻi ʻElepaio, and 161 Warbling white-eye. We were able to reliably sex 59 Kauaʻi ʻAmakihi, 46 ʻAnianiau, 105 Kauaʻi ʻElepaio, and 147 Warbling white-eye. Body Condition Multiple models appeared as equally competitive (ΔAICc ≤ 2) for all of the focal species (Table 1.2). At both 150m and 300m, the same top models emerged for Kauaʻi ʻAmakihi. These models were temperature alone, temperature + malaria (positive), temperature + malaria + TWI, and sex (M) + temperature + malaria. For Kauaʻi ʻAmakihi, a higher temperature during the previous mosquito breeding season was correlated with lower body condition, positive malarial status was correlated with higher body condition, higher TWI was associated with lower body condition, and male birds were associated with lower body condition. At both 150m and 300m the null model for ʻAnianiau was within ≤ 2 AICc for all top models, indicating that none of the tested stressors added information regarding body condition for this species. For Kauaʻi ʻElepaio, temperature and temperature + TWI were in top models at both 150m and 300m. At 300m, temperature + malaria + TWI appeared as an equally competitive model. Higher temperatures during the previous mosquito breeding season was associated with lower body condition for Kauaʻi ʻElepaio. For this species a higher TWI was correlated with lower body condition, and a positive malarial status was also associated with lower body condition. For the Warbling white- eye, at both 150 and 300m, temperature and temperature + TWI appeared in the top models. At 150m, temperature + TWI + canopy density appeared as an additional top model, while at 300m sex (M) + temperature appeared as an additional top model. For Warbling white-eye, higher temperatures during the previous mosquito breeding season and higher TWI were both correlated with lower body condition. Higher canopy densities were positively correlated with body condition, and male birds were negatively correlated with body condition (Table 1.2). 13 Sex None of the models evaluating the relationship between stressors and the probability of capturing female birds were < 2 AICc from the intercept only model (Table 1.3, Appendix). DISCUSSION Understanding how multiple stressors act individually or synergistically to influence the health and demographics of forest birds is important for sustaining and recovering island bird populations (Benning et al. 2002, Milenkaya et al. 2013, Fernández-Palacios et al. 2021). The purpose of this study was to determine if major stressors to island forest birds are influencing the health and demographics of the forest birds of Kauaʻi. This study suggests that out of six tested stressors, only the temperature during the previous mosquito breeding season and average topographic wetness were consistently negatively correlated with reduced body condition across multiple species (Figure 1.5; Table 1.4, Appendix). Malarial infection was negatively associated with body condition for two species, and positively associated with body condition for one species. Kauaʻi ʻAmakihi and ʻAnianiau were the only two species for which sex was associated with differences in body condition, and the direction of this relationship was inconsistent among these species. Contrary to predictions, there was no association between rodent control or extreme precipitation events and body condition for any of the tested species, nor was the probability of a captured bird being female associated with rodent control. These findings suggest that variables associated with disease prevalence may be the most influential in shaping the health of these forest bird populations, and that rodent control, at least at current levels of intensity, is not effective in improving forest bird health and demography in the Alakaʻi Wilderness Preserve. The outcomes of this study could help guide and prioritize management actions for Kauaʻi’s rapidly declining forest birds. Across all species, decreases in body condition were correlated with increases in the average temperatures during the mosquito season prior to when the bird was caught (Figure 1.6 & 1.7). This represents the first evidence that climate and disease could together have sub-lethal effects on forest birds on Kauaʻi. Mosquitoes that transmit disease such as avian malaria often have highly temperature dependent life history processes. Elevated temperatures can act as a catalyst and accelerate the development and life cycle of these insects, translating to increased 14 fecundity and higher overall mosquito abundance (Chuang et al. 2011, Ganser and Wisely 2013, Ciota et al. 2014). In contrast, colder temperatures have a suppressive effect on mosquito metabolic processes and lead to decreased mosquito activity. Consequently, behaviors that are crucial for reproduction such as flight, host-seeking, and blood feeding become hampered under colder conditions (Ganser and Wisely 2013, Reinhold et al. 2018, 2022). The cooler temperatures of high elevation forests in Hawaiʻi act as a natural barrier to mosquito expansion, effectively restricting the distribution of these malaria vectors to lower elevations. Consequently, most native Hawaiian forest bird species are restricted to higher elevations where they are protected from this potentially fatal disease. As temperatures increase with climate change, mosquito populations are more frequently being found at higher and higher elevations, and the refuge that these bird populations once had are shrinking (Lapointe et al. 2012, Liao et al. 2017). These results indicate that in addition to the direct mortality caused by avian malaria, there are also sub-lethal effects of rising temperatures and the accelerating risk of mosquito transmission at higher elevations. Topographic Wetness Index (TWI) is often positively associated with habitat quality for forest birds (Moeslund et al. 2013, Del-Toro-Guerrero et al. 2019, Xie et al. 2021), but had a slight association with poor body condition in this study (Figure 1.8). A possible explanation for this could be due to the potential effect of TWI on mosquito larval habitat availability. TWI is built on digital elevation models that predict the likelihood of moisture to pool in an area. Areas where the slope of the terrain leads to increased soil moisture are more likely to produce stagnant water, which provides ideal habitat for mosquito larvae (Ganser and Wisely 2013, Riihimäki et al. 2021). Ganser & Wisley (2013) tested a variety of environmental variables to see which were associated with mosquito abundance and diversity in a mixed grass prairie in Kansas. Of the variables tested, only TWI was significantly positively correlated with mosquito abundance in a mixed grass prairie in Kansas (Ganser & Wisley 2013). Similarly, Cohen et al. (2008) found that proximity to regions with higher wetness indices increased the risk of malaria transmission. For two out of the three native species in this study, positive malarial status was negatively associated with body condition (Figure 1.9). Hawaii’s native flycatchers are often less vulnerable to avian malaria compared to honeycreepers and can live with the disease without experiencing fatal effects (Vanderwerf et al. 2006). Nonetheless, my findings demonstrate that Kauaʻi ʻElepaio are still being affected on a sub-lethal level. Many introduced birds such as the https://paperpile.com/c/Iaa5rp/gVhB+kOae+AdXP https://paperpile.com/c/Iaa5rp/gVhB+kOae+AdXP https://paperpile.com/c/Iaa5rp/kOae+lbHy+oQEf https://paperpile.com/c/Iaa5rp/xluH+KOge 15 Warbling White-eye live with moderate levels of disease infection and are considered as reservoirs of avian malaria (McClure 2017). This is a likely reason why malarial infection did not appear in any of our top models for this species. Because honeycreepers are particularly susceptible to avian malaria (Paxton et al. 2022), it is unsurprising that although the correlation was not strong, avian malaria status was negatively correlated with body condition in all top models for ʻAnianiau, one of the two honeycreepers in this study. However, in contrast to predictions, the other honeycreeper species, Kauaʻi ʻAmakihi, was positively associated with malaria status. Some subpopulations of Hawaiʻi ʻAmakihi (Chlorodrepanis virens) have developed resistance to avian malaria and are able to coexist with mosquitoes that transmit avian malaria (Atkinson et al. 2013). It is possible that the Kauaʻi ‘Amakihi is developing resistance to this disease as well. Yet, given the absence of this species at lower elevations on Kauaʻi, a more likely explanation could be that malarial infection is reducing host activity and viability to a point where individuals with lower fitness that are testing positive for malaria are less likely to be captured. Malarial parasites may cause hosts to exhibit lethargic behaviors and reduce overall activity (Lapointe et al. 2012, Garamszegi et al. 2015), potentially leading to a reduction in capture rates (McPherson et al. 2012, Holmes et al. 2024). Higher body condition has been correlated with higher resistance to disease, and the ability to survive infection (Gleeson et al. 2005), therefore these individuals with higher fitness also would be more likely to be captured in nets. There is however opposing evidence that parasitic infections can also lead to increased foraging due to increased energetic demands and increased risk-taking behaviors that increase capture rates (Garamszegi et al. 2015, Remacha et al. 2023), therefore more research is warranted to determine why body condition in Kauaʻi ‘Amakihi is positively associated with avian malaria status. We found no correlations between avian malaria infection and sex in our focal species. These results align with literature, which is mixed on sex-related differences in malarial infection. For example, Garcial et al. (2023) found that the prevalence of malarial parasites was higher in males than in females for Red-legged partridges (Alectoris rufa) while Lachish et al. (2011) found malarial infection rates were greater for males than for females in Blue tits (Cyanistes caeruleus). Agh et al. (2019) found no sex related differences in malaria prevalence for European robins (Erithacus rubecula). 16 The relationship between body condition and sex was inconsistent among the two focal honeycreeper species. Several factors may contribute to these observed differences in body condition of males and females. Studies have revealed potential biases related to energy expenditure and breeding behaviors or avian life history (Bryant 1997, Hambly et al. 2007). The cost of reproduction for female birds may have significant impacts to their overall body condition. Additionally, birds that are sitting on nests or sleeping are often more vulnerable to depredation by arboreal rats. This can be sex dependent as many female birds preferentially incubate nests as in the case of Hawaiian honeycreeper species. Conversely, male birds may engage in more territorial defense behavior and may spend more time foraging leading to a higher energy expenditure and consequences to fitness and body condition. Energy expended on nest building can also vary between sexes and be dependent on species (Sibly et al. 2012, Jacobs et al. 2013, Mainwaring et al. 2021). It is possible that male Kauaʻi ʻAmakihi spend considerably more time foraging for resources and defending territory leading to a higher cost of fitness than females while female ʻAmakihi exhibit a higher cost of reproduction to fitness. Research on sex- specific time allocation for energy demanding behaviors in Honeycreepers is limited and warrants further investigation. Extreme precipitation was not in any of the top models across all species for body condition. Extreme weather has been known to have negative effects on tropical forest birds (Van Riper and Scott 2001, Şekercioğlu et al. 2012), but Kauaʻi’s forest birds evolved in forests which regularly experience high rainfall (Calhoun and Fletcher 1999, Paxton et al. 2016) and they may be adapted to these conditions. Additionally, the period in which we sampled for extreme precipitation could be insufficient to capture effects in body condition. Further, body condition may be better explained by extreme precipitation in other parts of the year, or perhaps by the number of sustained extreme precipitation events over a certain period prior to the birds’ capture. This study failed to show any relationship between rat trap density and body condition or the probability of a captured bird being female. This is in contrast with other studies that have found differences in both sex ratios and stress levels before and after the introduction of mammals, particularly in the case of island avian species (Clinchy et al. 2004, Slos and Stoks 2008, Donald 2011, Heinsohn et al. 2019, Weterings et al. 2022). It is possible that rodents are not influencing body condition and demography in this system, but trapping may also not be at 17 sufficient densities to see significant changes in our response variables (Nelson et al. 2002). Further, rat trap density is likely an imperfect measure of true rat abundance (Vanderwerf et al. 2011). Measuring abundance of small mammals at large scales is costly and logistically difficult and most methods of doing so have limitations (Sollmann et al. 2013, Palmer et al. 2018). Nonetheless, measuring rat densities more directly, or trapping at higher intensities may provide more insight into how invasive rodents influence body condition and demographics of Hawaiian forest birds. This study provides new insights into the stressors associated with sub-lethal effects on Kauaʻi’s forest birds. However, there are several factors that limit my inference, and highlight opportunities for future research. The strength of these relationships between stressors and body condition were marginal as demonstrated by R2 values (Table 1.2.). Other factors not tested in this study such as age, breeding status, or food availability in the environment may also be associated with body condition (Milenkaya et al. 2013, Deikumah et al. 2015). The age of captured birds was assessed upon banding, but the number of hatch year birds that were caught in this study were too low (0.06-33%) to test whether age could be a potential driver of body condition. Other factors potentially driving body condition in island forest birds, such as food availability, were beyond the scope of this study but should be explored in future research. Although I did not detect strong relationships between stressors and body condition, I suggest that the patterns and directions that emerged are of conservation relevance given that these species are relatively poorly understood and in crisis (Şekercioğlu et al. 2012). In addition to the constraints associated with our index of rat control, as discussed above, we were also limited by sample sizes. Although the sampling effort across the study areas within and outside of rodent controlled areas was consistent, the sampling effort throughout the years was variable, resulting in smaller sample sizes in year three (2023). Additionally, capture rates are particularly low for Kauaʻi’s forest birds (e.g., typically 0-7 birds/day with 4-10 nets in operation), perhaps because of rapidly declining populations (Crampton et al. 2022). ʻAnianiau had the lowest sample size (n=49), which could explain why this was the only species to not show strong correlations between the tested stressors and body condition. It is likely that a long- term study with sustained sampling effort could provide greater insight to the non-lethal effects of these stressors. Long-term monitoring of forest bird body condition could also improve overall understanding of how body condition varies with annual temperature and precipitation. 18 Conservation Recommendations Island birds play important ecological roles, contribute to global biodiversity, are central to the culture and history of islands (Paxton et al. 2022), and provide a source of enjoyment for residents and visitors (Steiner 2001). Yet, Hawaiian forest birds are facing a conservation crisis, and urgent action is needed to prevent further species extinction (Reed et al. 2012, Paxton et al. 2022). Conservation managers often face difficult decisions when deciding how to allocate limited conservation dollars (Pejchar et al. 2020). This study suggests that climatic and topographic factors associated with the spread of avian malaria may be the strongest predictors of body condition in Kauaʻi’s forest birds. If invasive mosquito populations are not controlled or eliminated rapidly, avian malaria infection will continue to spread with rising temperatures (Benning et al. 2002). A promising tool to reduce mosquito populations is a naturally occurring and symbiotic bacteria called Wolbachia (Pinto et al. 2021, Ogunlade et al. 2023, Velez et al. 2023). When mosquitoes with different strains of Wolbachia mate, eggs can be rendered infertile. The release of non-biting males with a different strain of Wolbachia than the wild population can reduce mosquito populations to near zero in treated areas (Werren 1997, Baldacchino et al. 2015). One of the challenges with this management action is the expense of implementing the treatment at large scales. Our finding that TWI is associated with poor body condition could indicate that targeted application of Wolbachia to these areas has the potential to be cost-effective. Immediate implementation of Wolbachia releases and other tools to mitigate against the effect of climate change and invasive disease will be critical to ensuring that Kauaʻi’s forest birds, and other island birds facing similar plights globally, are here for generations more to come. 19 TABLES AND FIGURES Table 1.2 The most competitive models within 2 AICc of the top AICc model explaining the association between stressor variables and body condition for Kauaʻi forest birds. Temperature = Mean temperature of mosquito breeding season prior to capture, Malaria = Positive malarial status, TWI = Mean Topographic Wetness Index, Sex = Male sex, Canopy Density = Mean canopy density. AICc = Akaike’s Information Criterion with small-sample bias adjustment (Burnham and Anderson 1998). Species Distance (m) Fixed effects AICc Marginal R2 Conditional R2 Kauaʻi ʻAmakihi 150 Temperature + Malaria (Positive) 283.4 0.118 0.360 Temperature + Malaria (Positive) + TWI 283.9 0.119 0.385 Temperature 285.2 0.064 0.288 Sex (M) + Temperature + Malaria (Positive) 285.3 0.124 0.383 Kauaʻi ʻAmakihi 300 Temperature + Malaria (Positive) 283.4 0.118 0.360 Temperature + Malaria (Positive) + TWI 284.1 0.117 0.376 Temperature 285.2 0.064 0.288 Sex (M) + Temperature + Malaria (Positive) 285.3 0.124 0.383 ʻAnianiau 150 Malaria (Positive) 143.3 0.082 0.755 Malaria (Positive) + TWI 143.4 0.111 0.784 20 Null Model 144.7 Temperature + Malaria (Positive) 144.9 0.093 0.777 Temperature + Malaria (Positive) + TWI 145.0 0.123 0.804 Temperature 145.1 0.034 0.778 ʻAnianiau 300 Malaria (Positive) 143.3 0.082 0.755 Malaria (Positive) + TWI 144.4 0.088 0.762 Null Model 144.7 Temperature + Malaria (Positive) 144.9 0.093 0.777 Temperature 145.1 0.034 0.778 Kauaʻi ʻElepaio 150 Temperature 411.7 0.075 0.370 Temperature + TWI 412.6 0.081 0.400 Kauaʻi ʻElepaio 300 Temperature 411.7 0.075 0.370 Temperature + TWI 411.8 0.085 0.400 Temperature + Malaria (Positive) + TWI 413.7 0.093 0.401 Warbling White-eye 150 Temperature + TWI 548.9 0.096 0.612 Temperature 549.8 0.082 0.575 Temperature + Canopy Density + TWI 550.2 0.126 0.578 Warbling White-eye 300 Temperature 549.8 0.082 0.575 21 Temperature + TWI 550.2 0.089 0.595 Sex (M) + Temperature 551.8 0.090 0.575 Figure 1.1. (a) Orange circles mark the study site locations (Halepaʻakai (HPK) and Mohihi (MOH)) for assessing the effect of multiple stressors on forest birds on the island of Kauaʻi, Hawaiʻi (U.S.A), and (b) black lines denote the boundaries of areas with rodent control at each location. 22 Figure 1.5. Infographic of variables that appeared in the top models for relationships between stressors and body condition. Symbols represent respective species, and positive or negative signs represent the direction of the correlation between body condition for that species and the stressor. * Stressors forʻAnianiau were not strongly correlated with body condition due to null model appearing amongst the top competitive models. 23 Figure 1.6. Relationship between body condition (SMI Score) and the average temperature during the mosquito breeding season prior to when the bird was caught for four focal bird species in the Alakaʻi Wilderness Preserve, Kauaʻi, Hawaiʻi. The solid lines represent the linear trend between body condition and temperature, with shaded areas indicating the 95% confidence intervals. 24 Figure 1.7. Relationship between the average temperature during the mosquito breeding season and body condition of birds. This figure displays the estimated marginal means of body condition for the temperature only mixed model across four focal bird species in the Alakaʻi Wilderness Preserve, Kauaʻi, Hawaiʻi. The temperature only model appeared as a top competitive model in all four species. 25 LITERATURE CITED Ágh, N., I. S. Piross, G. Majoros, T. Csörgő, and E. Szöllősi (2019). Malaria infection status of European Robins seems to associate with timing of autumn migration but not with actual condition. Parasitology 146:814–820. Amrhein, V., B. Scaar, M. Baumann, N. Minéry, J.-P. Binnert, and F. Korner-Nievergelt (2012). Estimating adult sex ratios from bird mist netting data. Methods in ecology and evolution / British Ecological Society 3:713–720. Ancona, S., A. Liker, M. C. Carmona-Isunza, and T. Székely (2020). Sex differences in age-to- maturation relate to sexual selection and adult sex ratios in birds. Evolution letters 4:44–53. Atkinson, C. T., R. J. Dusek, K. L. Woods, and W. M. Iko (2000). Pathogenicity of avian malaria in experimentally-infected Hawaii Amakihi. Journal of wildlife diseases 36:197–204. Atkinson, C. T., K. S. Saili, R. B. Utzurrum, and S. I. Jarvi (2013). Experimental evidence for evolved tolerance to avian malaria in a wild population of low elevation Hawai’i 'Amakihi (Hemignathus virens). EcoHealth 10:366–375. Atkinson, C. T., K. L. Woods, R. J. Dusek, L. S. Sileo, and W. M. Iko (1995). Wildlife disease and conservation in Hawaii: pathogenicity of avian malaria (Plasmodium relictum) in experimentally infected iiwi (Vestiaria coccinea). Parasitology 111 Suppl:S59–69. Baldacchino, F., B. Caputo, F. Chandre, A. Drago, A. della Torre, F. Montarsi, and A. Rizzoli (2015). Control methods against invasive Aedes mosquitoes in Europe: a review: Control methods against invasiveAedesmosquitoes in Europe. Pest management science 71:1471–1485. Bambini, G., E. Schlicht, and B. Kempenaers (2019). Patterns of female nest attendance and male feeding throughout the incubation period in Blue TitsCyanistes caeruleus. The Ibis 161:50– 65. Banko, P. C., K. A. Jaenecke, R. W. Peck, and K. W. Brinck (2019). Increased nesting success of Hawaii Elepaio in response to the removal of invasive black rats. The Condor 121. Banko, P. D., R. E. David, J. D. Jacobi, and W. E. Banko (2001). Conservation status and recovery strategies for endemic Hawaiian birds. Studies in Avian Biology 22:359–376. Barnett, C. A., T. N. Suzuki, S. K. Sakaluk, and C. F. Thompson (2015). Mass-based condition measures and their relationship with fitness: in what condition is condition? Journal of zoology 296:1–5. Bellard, C., P. Cassey, and T. M. Blackburn (2016). Alien species as a driver of recent extinctions. Biology letters 12:20150623. Benning, T. L., D. LaPointe, C. T. Atkinson, and P. M. Vitousek (2002). Interactions of climate change with biological invasions and land use in the Hawaiian Islands: Modeling the fate of 26 endemic birds using a geographic information system. Proceedings of the National Academy of Sciences of the United States of America 99:14246–14249. Benson, T. J., and J. C. Bednarz (2010). Relationships Among Survival, Body Condition, and Habitat of Breeding Swainson’s Warblers. The Condor 112:138–148. Blackwell, G. L., M. A. Potter, and J. A. McLennan (2002). Rodent density indices from tracking tunnels, snap-traps and Fenn traps: do they tell the same story? New Zealand journal of ecology 26:43–51. Bryant, D. M. (1997). Energy expenditure in wild birds. The Proceedings of the Nutrition Society 56:1025–1039. Burnham, K. P., and D. R. Anderson (2013). Model Selection and Multimodel Inference. Springer New York. Calhoun, R. S., and C. H. Fletcher III (1999). Measured and predicted sediment yield from a subtropical, heavy rainfall, steep-sided river basin: Hanalei, Kauai, Hawaiian Islands. Geomorphology (Amsterdam, Netherlands) 30:213–226. Catfolis, B., T. Vanroy, K. Verheyen, L. Baeten, A. Martel, F. Pasmans, D. Strubbe, and L. Lens (2023). Avian nutritional condition increases with forest structural complexity. Ecological indicators 154:110536. Chuang, T.-W., M. B. Hildreth, D. L. Vanroekel, and M. C. Wimberly (2011). Weather and land cover influences on mosquito populations in Sioux Falls, South Dakota. Journal of medical entomology 48:669–679. Ciota, A. T., A. C. Matacchiero, A. M. Kilpatrick, and L. D. Kramer (2014). The effect of temperature on life history traits of Culex mosquitoes. Journal of medical entomology 51:55–62. Clinchy, M., L. Zanette, R. Boonstra, J. C. Wingfield, and J. N. M. Smith (2004). Balancing food and predator pressure induces chronic stress in songbirds. Proceedings of the Royal Society of London. Series B: Biological Sciences 271:2473–2479. Cohen, J. M., K. C. Ernst, K. A. Lindblade, J. M. Vulule, C. C. John, and M. L. Wilson (2008). Topography-derived wetness indices are associated with household-level malaria risk in two communities in the western Kenyan highlands. Malaria journal 7:40. Courchamp, F., J.-L. Chapuis, and M. Pascal (2003). Mammal invaders on islands: impact, control and control impact. Biological reviews of the Cambridge Philosophical Society 78:347– 383. Crampton, L. H., M. K. Reeves, T. Bogardus, E. M. Gallerani, T. A. Winter, and A. B. Shiels (2022). Modifications to prevent non-target lethality of Goodnature A24 rat traps – effects on rodent kill rates. Management of biological invasions: international journal of applied research on biological invasions 13. 27 Culliney, S., L. Pejchar, R. Switzer, and V. Ruiz-Gutierrez (2012). Seed dispersal by a captive corvid: the role of the “Alalā (Corvus hawaiiensis) in shaping Hawai”i’s plant communities. Ecological applications: a publication of the Ecological Society of America 22:1718–1732. Deikumah, J. P., C. A. McAlpine, and M. Maron (2015). Matrix Intensification Affects Body and Physiological Condition of Tropical Forest-Dependent Passerines. PloS one 10:e0128521. Del-Toro-Guerrero, F. J., T. Kretzschmar, and S. H. Bullock (2019). Precipitation and topography modulate vegetation greenness in the mountains of Baja California, México. International journal of biometeorology 63:1425–1435. Doherty, T. S., A. S. Glen, D. G. Nimmo, E. G. Ritchie, and C. R. Dickman (2016). Invasive predators and global biodiversity loss. Proceedings of the National Academy of Sciences of the United States of America 113:11261–11265. Domènech, J., and J. C. Senar (1998). Trap Type Can Bias Estimates of Sex Ratio (El Tipo de Trampa Puede Sesgar los Estimados de la Proporción de Sexos). Journal of field ornithology 69:380–385. Donald, P. F. (2011). Lonely males and low lifetime productivity in small populations: Adult sex ratios and lifetime reproductive success. The Ibis 153:465–467. Ediriweera, S., T. Danaher, and S. Pathirana (2016). The influence of topographic variation on forest structure in two woody plant communities: A Remote Sensing approach. Forest systems 25. English, M. D., G. J. Robertson, L. E. Peck, D. Pirie-Hay, S. Roul, and M. L. Mallory (2018). Body condition of American Black Ducks (Anas rubripes) wintering in Atlantic Canada using carcass composition and a scaled mass index. Canadian journal of zoology 96:1137–1144. Fernández-Palacios, J. M., H. Kreft, S. D. H. Irl, S. Norder, C. Ah-Peng, P. A. V. Borges, K. C. Burns, L. de Nascimento, J.-Y. Meyer, E. Montes, and D. R. Drake (2021). Scientists’ warning - The outstanding biodiversity of islands is in peril. Global ecology and conservation 31:e01847. Fontaine, J. J., and T. E. Martin (2006). Parent birds assess nest predation risk and adjust their reproductive strategies. Ecology letters 9:428–434. Fortini, L. B., A. E. Vorsino, F. A. Amidon, E. H. Paxton, and J. D. Jacobi (2015). Large-Scale Range Collapse of Hawaiian Forest Birds under Climate Change and the Need for 21st Century Conservation Options [corrected]. PloS one 10:e0140389. Foster, J. T., E. J. Tweed, R. J. Camp, B. L. Woodworth, C. D. Adler, and T. Telfer (2004). Long-Term Population Changes of Native and Introduced Birds in the Alaka’i Swamp, Kaua’i. Conservation Biology 18:716–725. Freed, L. A., and R. L. Cann (2014). Diffuse competition can be reversed: a case history with birds in Hawaii. Ecosphere 5:art147. 28 Fretz, S. J. (2002). Scales of Food Availability for an Endangered Insectivore, the Hawaii Akepa. The Auk 119:166–174. Fricker, G. A., L. H. Crampton, E. M. Gallerani, J. M. Hite, R. Inman, and T. W. Gillespie (2021). Application of lidar for critical endangered bird species conservation on the island of Kauai, Hawaii. Ecosphere 12. Ganser, C., and S. M. Wisely (2013). Patterns of spatio-temporal distribution, abundance, and diversity in a mosquito community from the eastern Smoky Hills of Kansas. Journal of vector ecology: journal of the Society for Vector Ecology 38:229–236. Garamszegi, L. Z., M. Zagalska-Neubauer, D. Canal, G. Markó, E. Szász, S. Zsebők, E. Szöllősi, G. Herczeg, and J. Török (2015). Malaria parasites, immune challenge, MHC variability, and predator avoidance in a passerine bird. Behavioral ecology: official journal of the International Society for Behavioral Ecology 26:1292–1302. García, J. T., L. Pérez-Rodríguez, M. Calero-Riestra, I. Sánchez-Barbudo, J. Viñuela, and F. Casas (2023). Sexual differences in blood parasite infections, circulating carotenoids and body condition in free‐living red‐legged partridges. Journal of zoology (London, England: 1987) 320:260–270. Gleeson, D. J., M. W. Blows, and I. P. F. Owens (2005). Genetic covariance between indices of body condition and immunocompetence in a passerine bird. BMC evolutionary biology 5:61. Gon, S. ’ohukani'ohi'a, III, and K. B. Winter (2019). A Hawaiian Renaissance That Could Save the World: This archipelago’s society before Western contact developed a large, self-sufficient population, yet imposed a remarkably small ecological footprint. American scientist 107:232+. Gronwald, M., and J. Russell (2021). Measuring rat relative abundance using camera traps and digital strike counters for Goodnature A24 self-resetting traps. New Zealand journal of ecology. https://doi.org/10.20417/nzjecol.45.7 Guest, S. J. (1973). Reproductive Biology of Japanese White - Eye. University of Hawaii 29. Hambly, C., S. Markman, L. Roxburgh, and B. Pinshow (2007). Seasonal sex–specific energy expenditure in breeding and non‐breeding Palestine sunbirds Nectarinia osea. Journal of avian biology 38:190–197. Harper, G. A., and N. Bunbury (2015). Invasive rats on tropical islands: Their population biology and impacts on native species. Global Ecology and Conservation 3:607–627. Heinsohn, R., G. Olah, M. Webb, R. Peakall, and D. Stojanovic (2019). Sex ratio bias and shared paternity reduce individual fitness and population viability in a critically endangered parrot. The Journal of animal ecology 88:502–510. Hinsley, S. A., R. A. Hill, P. E. Bellamy, and H. Balzter (2006). The Application of Lidar in Woodland Bird Ecology. Photogrammetric Engineering & Remote Sensing 72:1399–1406. 29 Holmes, I. A., A. M. Durso, C. R. Myers, and T. A. Hendry (2024). Changes in capture availability due to infection can lead to detectable biases in population-level infectious disease parameters. PeerJ 12:e16910. Jacobs, S. R., K. H. Elliott, and A. J. Gaston (2013). Parents are a drag: long-lived birds share the cost of increased foraging effort with their offspring, but males pass on more of the costs than females. PloS one 8:e54594. Kalluri, S., P. Gilruth, D. Rogers, and M. Szczur (2007). Surveillance of arthropod vector-borne infectious diseases using remote sensing techniques: a review. PLoS pathogens 3:1361–1371. Karels, T. J., F. S. Dobson, H. S. Trevino, and A. L. Skibiel (2008). The Biogeography of Avian Extinctions on Oceanic Islands. Journal of biogeography 35:1106–1111. Kaushik, M., L. Pejchar, and L. H. Crampton (2018). Potential disruption of seed dispersal in the absence of a native Kauai thrush. PloS one 13:e0191992. Labocha, M. K., and J. P. Hayes (2012). Morphometric indices of body condition in birds: a review. Journal of ornithology / DO-G 153:1–22. Lachish, S., S. C. L. Knowles, R. Alves, M. J. Wood, and B. C. Sheldon (2011). Infection dynamics of endemic malaria in a wild bird population: parasite species-dependent drivers of spatial and temporal variation in transmission rates: Infection dynamics of endemic avian malaria. The journal of animal ecology 80:1207–1216. Lapointe, D. A., C. T. Atkinson, and M. D. Samuel (2012). Ecology and conservation biology of avian malaria. Annals of the New York Academy of Sciences 1249:211–226. Lavers, J. L., C. Wilcox, and C. Josh Donlan (2010). Bird demographic responses to predator removal programs. Biological invasions 12:3839–3859. Liao, W., C. T. Atkinson, D. A. LaPointe, and M. D. Samuel (2017). Mitigating Future Avian Malaria Threats to Hawaiian Forest Birds from Climate Change. PloS one 12:e0168880. Mainwaring, M. C., J. Nagy, and M. E. Hauber (2021). Sex-specific contributions to nest building in birds. Behavioral ecology: official journal of the International Society for Behavioral Ecology 32:1075–1085. Matthews, T. J., J. P. Wayman, P. Cardoso, F. Sayol, J. P. Hume, W. Ulrich, J. A. Tobias, F. C. Soares, C. Thébaud, T. E. Martin, and K. A. Triantis (2022). Threatened and extinct island endemic birds of the world: Distribution, threats and functional diversity. Journal of biogeography 49:1920–1940. McCloy, M. W. D., S. Glasscock, and J. K. Grace (2023). Local weather affects body condition of three North American songbird species on the Texas Coast. Ecology and evolution 13:e10317. McCloy, M. W. D., and J. K. Grace (2023). Short-term weather patterns influence avian body condition during the breeding season. Frontiers in Ecology and Evolution 11. 30 McClure, K. M. (2017). Disease Ecology of Avian Malaria in Native and Introduced Birds in Lowland Hawaii. [Online.] Available at https://www.proquest.com/docview/1961292383/abstract?parentSessionId=YEUggUOnqhqpDy 59q%2F%2B9EiZRW4jbw90z21DeFmxzv9w%3D&pq- origsite=primo&accountid=10223&sourcetype=Dissertations%20&%20Theses. McPherson, N. J., R. A. Norman, A. S. Hoyle, J. E. Bron, and N. G. H. Taylor (2012). Stocking methods and parasite-induced reductions in capture: modelling Argulus foliaceus in trout fisheries. Journal of theoretical biology 312:22–33. Milenkaya, O., N. Weinstein, S. Legge, and J. R. Walters (2013). Variation in body condition indices of crimson finches by sex, breeding stage, age, time of day, and year. Conservation physiology 1:cot020. Moeslund, J. E., L. Arge, P. K. Bøcher, T. Dalgaard, M. V. Odgaard, B. Nygaard, and J.-C. Svenning (2013). Topographically controlled soil moisture is the primary driver of local vegetation patterns across a lowland region. Ecosphere (Washington, D.C) 4:art91. Molina-Marin, D. A., J. C. Rodas-Rua, C. E. Lara, F. A. Rivera-Páez, F. E. Fontúrbel, G. J. Castaño-Villa, [email protected], Laboratório de Biogeografia da Conservação e Macroecologia, Universidade Federal do Pará, Belém 66075-110, PA, Brazil, [email protected], [email protected], [email protected], and [email protected] (2022). Effects of Landscape Configuration on the Body Condition of Migratory and Resident Tropical Birds. Diversity 14:432. Moors, P. J., I. A. E. Atkinson, and G. H. Sherley (1992). Reducing the rat threat to island birds. Bird conservation international 2:93–114. Morrison, C. A., R. A. Robinson, J. A. Clark, and J. A. Gill (2016). Causes and consequences of spatial variation in sex ratios in a declining bird species. The Journal of animal ecology 85:1298– 1306. Mosher, S. M., J. L. Rohrer, V. Costello, M. D. Burt, M. Keir, J. Beachy, H. K. Kawelo, and M. Mansker (2010). Rat control for the protection of endangered birds, plants, and tree snails on the Island of Oahu, Hawaii. Proceedings of the Vertebrate Pest Conference 24. Nadal, J., C. Ponz, and A. Margalida (2016). Age and Sex Ratios in a High-Density Wild Red- Legged Partridge Population. PloS one 11:e0159765. Nelson, J. T., B. Woodworth, S. Fancy, G. D. Lindsey, and E. J. Tweed (2002). Effectiveness of rodent control and monitoring techniques for a montane rainforest. Wildlife Society Bulletin 30:82–92. Ogunlade, S. T., A. I. Adekunle, M. T. Meehan, and E. S. McBryde (2023). Quantifying the impact of Wolbachia releases on dengue infection in Townsville, Australia. Scientific reports 13:14932. 31 Økland, R. H., K. Rydgren, and T. Ø kland (2008). Species richness in boreal swamp forests of SE Norway: The role of surface microtopography. Journal of vegetation science: official organ of the International Association for Vegetation Science 19:67–74. Palmer, M. S., A. Swanson, M. Kosmala, T. Arnold, and C. Packer (2018). Evaluating relative abundance indices for terrestrial herbivores from large-scale camera trap surveys. African journal of ecology 56:791–803. Paxton, E. H., R. J. Camp, P. M. Gorresen, L. H. Crampton, D. L. Leonard Jr, and E. A. VanderWerf (2016). Collapsing avian community on a Hawaiian island. Science advances 2:e1600029. Paxton, E. H., M. Laut, S. Enomoto, and M. Bogardus (2022). Hawaiian forest bird conservation strategies for minimizing the risk of extinction: Biological and biocultural considerations. HCSU-103. Peig, J., and A. J. Green (2009). New perspectives for estimating body condition from mass/length data: the scaled mass index as an alternative method. Oikos 118:1883–1891. Peig, J., and A. J. Green (2010). The paradigm of body condition: a critical reappraisal of current methods based on mass and length. Functional ecology 24:1323–1332. Pinto, S. B., T. I. S. Riback, G. Sylvestre, G. Costa, J. Peixoto, F. B. S. Dias, S. K. Tanamas, C. P. Simmons, S. M. Dufault, P. A. Ryan, S. L. O’Neill, et al. (2021). Effectiveness of Wolbachia- infected mosquito deployments in reducing the incidence of dengue and other Aedes-borne diseases in Niterói, Brazil: A quasi-experimental study. PLoS neglected tropical diseases 15:e0009556. Post, A. K., K. P. Davis, J. LaRoe, D. L. Hoover, and A. K. Knapp (2021). Semiarid grasslands and extreme precipitation events: do experimental results scale to the landscape? Ecology 102:e03437. Pratt, T. K., C. T. Atkinson, P. C. Banko, B. L. Woodworth, and J. D. Jacobi (2009). Conservation Biology of Hawaiian Forest Birds: Implications for Island Avifauna. Yale University Press. Raine, A. F., S. Driskill, M. Vynne, D. Harvey, and K. Pias (2020). Managing the effects of introduced predators on Hawaiian endangered seabirds. The Journal of wildlife management 84:425–435. R Core Team (2023). R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria. . Reed, M.J., D.W. DesRochers, E. A. VanderWerf, and J. M. Scott (2012). Long-Term Persistence of Hawaii’s Endangered Avifauna through Conservation-Reliant Management. Bioscience 62:881–892. 32 Reidy, J. L., M. M. Stake, and F. R. Thompson III (2009). Nocturnal Predation of Females on Nests: An Important Source of Mortality for Golden-cheeked Warblers? The Wilson journal of ornithology 121:416–421. Reinhold, J. M., K. Chandrasegaran, H. Oker, J. E. Crespo, C. Vinauger, and C. Lahondère (2022). Species-specificity in thermopreference and CO2-gated heat-seeking in Culex mosquitoes. Insects 13:92. Reinhold, J. M., C. R. Lazzari, and C. Lahondère (2018). Effects of the Environmental Temperature on Aedes aegypti and Aedes albopictus Mosquitoes: A Review. Insects 9:158. Remacha, C., Á. Ramírez, E. Arriero, and J. Pérez-Tris (2023). Haemosporidian infections influence risk-taking behaviours in young male blackcaps, Sylvia atricapilla. Animal behaviour 196:113–126. Remeš, V., and L. Harmáčková (2018). Disentangling direct and indirect effects of water availability, vegetation, and topography on avian diversity. Scientific reports 8:15475. Riihimäki, H., J. Kemppinen, M. Kopecký, and M. Luoto (2021). Topographic wetness index as a proxy for soil moisture: The importance of flow‐routing algorithm and grid resolution. Water resources research 57. van Riper, C. (1995). Ecology and Breeding Biology of the Hawaii Elepaio (Chasiempis sandwichensis bryani). The Condor 97:512–527. Rodrigues, J. F. M., and M. T. P. Coelho (2016). Differences in movement pattern and detectability between males and females influence how common sampling methods estimate sex ratio. PloS one 11:e0159736. Ruscoe, W. A., R. Goldsmith, and D. Choquenot (2001). A comparison of population estimates and abundance indices for house mice inhabiting beech forests in New Zealand. Wildlife research (East Melbourne, Melbourne, Vic.) 28:173. Russel, J. C., and N. D. Holmes (2015). Tropical island conservation: Rat eradication for species recovery. Biological conservation 185:1–7. Russell, J. C., and C. Kueffer (2019). Island Biodiversity in the Anthropocene. Annual review of environment and resources 44:31–60. Samuel, M. D., B. L. Woodworth, C. T. Atkinson, P. J. Hart, and D. A. LaPointe (2015). Avian malaria in Hawaiian forest birds: infection and population impacts across species and elevations. Ecosphere 6:art104. Sauve, D., V. L. Friesen, and A. Charmantier (2021). The Effects of Weather on Avian Growth and Implications for Adaptation to Climate Change. Frontiers in Ecology and Evolution 9. Scheffers, B. R., D. P. Edwards, A. Diesmos, S. E. Williams, and T. A. Evans (2014). Microhabitats reduce animal’s exposure to climate extremes. Global change biology 20:495–503. 33 Schulte-Hostedde, A. I., B. Zinner, J. S. Millar, and G. J. Hickling (2005). Restitution of mass– size residuals: Validating body condition indices. Ecology 86:155–163. Şekercioğlu, Ç. H., R. B. Primack, and J. Wormworth (2012). The effects of climate change on tropical birds. Biological conservation 148:1–18. Shiels, A. B., and D. R. Drake (2015). Barriers to seed and seedling survival of once-common Hawaiian palms: the role of invasive rats and ungulates. AoB plants 7. Sibly, R. M., C. C. Witt, N. A. Wright, C. Venditti, W. Jetz, and J. H. Brown (2012). Energetics, lifestyle, and reproduction in birds. Proceedings of the National Academy of Sciences of the United States of America 109:10937–10941. Simberloff, D. (2006). Invasional meltdown 6 years later: important phenomenon, unfortunate metaphor, or both? Ecology letters 9:912–919. Slos, S., and R. Stoks (2008). Predation risk induces stress proteins and reduces antioxidant defense. Functional ecology 22:637–642. Smetzer, J. R., K. L. Paxton, and E. H. Paxton (2021). Individual and seasonal variation in the movement behavior of two tropical nectarivorous birds. Movement ecology 9:36. Sollmann, R., A. Mohamed, H. Samejima, and A. Wilting (2013). Risky business or simple solution – Relative abundance indices from camera-trapping. Biological conservation 159:405– 412. Soriano-Redondo, A., S. Bearhop, I. R. Cleasby, L. Lock, S. C. Votier, and G. M. Hilton (2016). Ecological Responses to Extreme Flooding Events: A Case Study with a Reintroduced Bird. Scientific reports 6:28595. Steiner, W. W. M. (2001). Evaluating the Cost of Saving Native Hawaiian Birds. Studies in avian biology 22:377–383. Tweed, E. J., J. T. Foster, B. L. Woodworth, P. Oesterle, C. Kuehler, A. A. Lieberman, A. Tracey Powers, K. Whitaker, W. B. Monahan, J. Kellerman, and T. Telfer (2003). Survival, dispersal, and home-range establishment of reintroduced captive-bred puaiohi, Myadestes palmeri. Biological Conservation. [Online.] Available at http://dx.doi.org/10.1016/s0006- 3207(02)00175-1. Vanderwerf, E. A. (2012). Evolution of nesting height in an endangered Hawaiian forest bird in response to a non-native predator. Conservation biology: the journal of the Society for Conservation Biology 26:905–911. Vanderwerf, E. A., M. D. Burt, J. L. Rohrer, and S. M. Mosher (2006). Distribution and prevalence of mosquito-borne diseases in O’ahu ’Elepaio. The condor 108:770–777. Vanderwerf, E. A., M. T. Lohr, A. J. Titmus, P. E. Taylor, and M. D. Burt (2013). Current distribution and abundance of the O‘ahu ‘Elepaio (Chasiempis ibidis). The Wilson Journal of Ornithology 125:600–608. 34 Van Riper, C., III, and M. J. Scott (2001). Limiting Factors Affecting Hawaiian Native Birds. Studies in Avian Biology No. 22:221–233. Velez, I. D., A. Uribe, J. Barajas, S. Uribe, S. Ángel, J. D. Suaza-Vasco, M. C. Mejia Torres, M. P. Arbeláez, E. Santacruz-Sanmartin, L. Duque, L. Martínez, et al. (2023). Large-scale releases and establishment of wMel Wolbachia in Aedes aegypti mosquitoes throughout the Cities of Bello, Medellín and Itagüí, Colombia. PLoS neglected tropical diseases 17:e0011642. Werren, J. H. (1997). Biology of Wolbachia. Annual review of entomology 42:587–609. Westergaard, G. (2022). Hidden Stories of Extinction: Hawaiian ʻAhuʻula Feather Capes as Biocultural Artefacts. Museum and Society 20:104–117. Weterings, M. J. A., S. Losekoot, H. J. Kuipers, H. H. T. Prins, F. van Langevelde, and S. E. van Wieren (2022). Influence of multiple predators decreases body condition and fecundity of European hares. Ecology and evolution 12:e8442. Whelan, C. J., D. G. Wenny, and R. J. Marquis (2008). Ecosystem services provided by birds. Annals of the New York Academy of Sciences 1134:25–60. Witmer, G. W., W. C. Pitt, and G. Howald (2014). Invasive rodent ecology, impacts, and management with an emphasis on the United States. Proceedings of the Vertebrate Pest Conference 26. Xie, X., J. M. Chen, P. Gong, and A. Li (2021). Spatial scaling of gross primary productivity over sixteen mountainous watersheds using vegetation heterogeneity and surface topography. Journal of geophysical research. Biogeosciences 126:e2020JG005848. Yorinks, N., and C. T. Atkinson (2000). Effects of Malaria on Activity Budgets of Experimentally Infected Juvenile Apapane (Himatione sanguinea). The Auk 117:731–738. 35 CHAPTER TWO - EVALUATING THE EFFECT OF INVASIVE RAT CONTROL ON HABITAT REGENERATION FOR KAUAʻI’S FOREST BIRDS SUMMARY Introduced rats can have detrimental impacts on forest regeneration processes, with consequences for other trophic levels. Rats frequently consume or damage fruit, seeds, and seedlings, which can disrupt ecosystem processes that provide food and habitat for bird populations. These impacts are exacerbated on oceanic islands where plants and animals have evolved without mammalian herbivores and seed predators, and many native species are at risk of extinction due to invasive species and other stressors. The goal of this study was to evaluate the relationship between rodent control and three variables, fruiting density, seed rain, and seedling emergence, that influence forest regeneration processes in the Alakaʻi Wilderness Preserve on Kauaʻi Island, Hawaiʻi (U.S.A.). This area is one of the last remaining refuges for Kauaʻi’s native forest birds. Seed traps and seedling emergence plots were set in areas with and without rodent control, and seed rain, fruiting density, and seedling emergence were monitored at and adjacent to these plots from February - June 2024. We found no difference in seed rain, seedling emergence, or fruiting density inside and outside of areas of rodent control. These findings suggest that, at least at current levels of rodent control, this management action has not significantly influenced forest regeneration processes in the Alakaʻi Wilderness Preserve. If these findings are consistent at higher, more sustained levels of rodent control, it may be beneficial to focus conservation funds on reducing or eradicating other invasive taxa, such as ungulates and plants, to improve native forest bird habitat on Kauaʻi. INTRODUCTION Rats are often considered a major threat to island biodiversity, due to their ability to adapt to and exploit diverse environments (Keitt et al. 2015). They are agile, have a high reproductive rate, can exist in many different types of habitats, and are omnivorous and opportunistic foragers that are able to exploit most food resources (Witmer et al. 2014, Harper and Bunbury 2015, Duron et al. 2017a). Higher rainfall and primary productivity found in insular ecosystems may https://paperpile.com/c/Iaa5rp/3trGO https://paperpile.com/c/Iaa5rp/5PdZ+VFLS+xLhuB https://paperpile.com/c/Iaa5rp/5PdZ+VFLS+xLhuB 36 also lead to higher densities in rat populations due to an abundance of food resources throughout the year (Harper and Bunbury 2015). Their ability to establish and invade new areas is further enabled by the frequent absence of competition, because islands are often too isolated to have native mammal populations (Doherty et al. 2016). Invasive rats can change the trophic structures of communities, and this may lead to negative indirect impacts on the species that rely on these ecological processes (Ringler et al. 2015) and play a role in maintaining them (Mäntylä et al. 2011). Rats consume all stages of plants from seeds to adults (Wolf et al. 2018), and over half of the diet of rats often consists of plant material (Harper and Bunbury 2015). Seeds and seedlings are preferred over other plant parts, likely due to the higher energy and nutrient concentration of seeds. Predation of seeds is likely the biggest influence that rats inflict on forest composition and structure in ecosystems. Rats can disrupt bird-mediated seed dispersal by destroying the seeds of plants past the point of viability (Grant-Hoffman and Barboza 2010). The high reproductive potential of rats (Witmer et al. 2014) combined with their voracious feeding habits can lead to overconsumption of native seed banks and seedlings (Harper and Bunbury 2015) thus playing a role in seed dispersal limitation (Kaushik et al. 2018) and diminished recruitment of native plants (Grant-Hoffman and Barboza 2010, Shiels and Drake 2011, Harper and Bunbury 2015), contributing to a form of invasional meltdown (Simberloff 2006). Rat removal can help restore and maintain plant community composition and ecosystem function (Grant-Hoffman et al. 2010). For example, rats were identified as one of the top reasons for lack of recruitment of an extremely endangered Hawaiian plant hau kuahiwi (Hibiscadelphus giffardianus). After rat removal the mean retention of fruit for the plant was more than doubled from pre-treatment levels (Gill et al. 2018). On Palmyra Atoll, seedling recruitment increased for five out of six native tree species that were studied after the eradication of rats from the island (Wolf et al. 2018). Similarly, on the island of Oahu in Hawaiʻi, an endangered native palm (Pritchardia kaale) went from almost zero juveniles to close to 1,600 individuals in only a few years after goats were removed and rats were suppressed. On Breaksea Island in Fiordland, New Zealand, where rats were responsible for declines in recruitment of Nothofagus and other tree and shrub species, forests saw an increase in the number of seedlings following rat removal (Allen et al. 1994). https://paperpile.com/c/Iaa5rp/VFLS https://paperpile.com/c/Iaa5rp/qct6 https://paperpile.com/c/Iaa5rp/8lwla https://paperpile.com/c/Iaa5rp/uMLJy https://paperpile.com/c/Iaa5rp/uMLJy https://paperpile.com/c/Iaa5rp/lcMT1 https://paperpile.com/c/Iaa5rp/VFLS https://paperpile.com/c/Iaa5rp/tZ3hG https://paperpile.com/c/Iaa5rp/5PdZ https://paperpile.com/c/Iaa5rp/VFLS https://paperpile.com/c/Iaa5rp/2cyQn https://paperpile.com/c/Iaa5rp/tZ3hG+VFLS+x0hrZ https://paperpile.com/c/Iaa5rp/sgYZL https://paperpile.com/c/Iaa5rp/ftNlX https://paperpile.com/c/Iaa5rp/EUeHJ https://paperpile.com/c/Iaa5rp/lcMT1 https://paperpile.com/c/Iaa5rp/L0LSp 37 Studying changes in forest health following rat control can provide valuable information about the effect of introduced predators on trophic interactions. The objective of this study was to assess how invasive rodent control affects habitat structure and resource availability for Kauaʻiʻs native forest birds in the Alakaʻi Wilderness Preserve. To do this, I evaluated the relationship between rodent control and three forest regeneration processes that contribute to food and habitat availability for forest birds: fruit density, seed rain, and seedling emergence. The results of this study could help guide management actions to improve quality for Kauaʻi’s forest bird populations, and other island communities facing similar threats. METHODS Study Area This study was located in the Alakaʻi Wilderness preserve on Kauaʻi Island, Hawaiʻi (U.S.A). The preserve is a wet montane forest that contains some of the most intact native forest on the island and serves as a refuge and sanctuary for many of the islands’ remaining native flora and fauna. The Kauaʻi Forest Bird Recovery Project (KFBRP) established two areas within the preserve to control rat populations with self-resetting Goodnature A24 rat traps (http://goodnature.co.nz). My research questions were addressed in one of these areas, Halepaʻakai (HPK; Figure 2.1) from February - June 2023. Halepaʻakai was chosen because it is the only site that includes areas with and without rodent control that is also fenced to exclude non-native ungulates (e.g., feral pigs (Sus scrofa)). Ungulates disturb the soil surface and consume plants, affecting seed emergence and seedling survival (Hart et al. 2020). The rodent control grid has approximately 164 traps and has been operating continuously since March 2015. Previous research in this study area have used tracking tunnels as a proxy for relative abundance and have shown that relative rat abundance is substantially lower on the rat grid compared to areas without rodent control (Crampton et al. 2022). Halepaʻakai is at an elevation of ~1300m with an average rainfall of 13m per year. The dominant vegetation at this study site is ʻōhiʻa lehua (Metrosideros polymorpha) in the canopy and lapalapa (Cheirodendron platyphyllum), ʻōlapa (Cheirodendron trigynum), ʻōhiʻa hā (Syzygium sandwicensis), kāwaʻu (Ilex anomala), alani (Melicope spp.), and manono (Kadua terminalis) in the canopy and sub-canopy. The understory has various other native woody plants 38 such as pilo (Coprosoma spp.), pūkiawe (Styphelia tameiameiae) ʻukiʻuki (Dianella sandwicensis) hāhāʻaiakamanau (Clermontia fauriei) ʻōhelo (Vaccinium calycinum), and ʻohe naupaka (Scaevola glabra). Prominent invasive plants are himalayan ginger (Hedychium gardnerianum), blackberry (Rubus argutus), thimbleberry (Rubus parviflorus) and strawberr