Project

The Movement Ecology and Conservation of the Hawaiian gallinule (Gallinula galeata sandvicensis)

Goal: Integrating population genetics, landscape genetics, radio telemetry, and mark-resight studies to understand the impacts of anthropogenic landscape change on the movement behavior and population structure of an endangered Hawaiian waterbird. Comparing commonly used field methods for estimating movement, and statistical methods for estimating functional and structural population connectivity.

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Project log

Charles van Rees
added a research item
A key component for biologists managing mobile species is understanding where and when a species occurs at different locations and scaling management to fit the spatial and temporal patterns of movement. We established an automated radio‐telemetry tracking network to document multi‐year movement in 2016–2018 of 3 endangered waterbirds among wetlands on Oʻahu, Hawaiʻi, USA: ʻalae ʻula or Hawaiian gallinule (gallinule; Gallinula galeata sandvicensis), ʻalae keʻokeʻo or Hawaiian coot (coot; Fulica alai), and aeʻo or Hawaiian stilt (stilt; Himantopus mexicanus knudseni), each with different ecological requirements. There were marked differences in the movement propensity of the species, with no movement among sites detected in gallinules, 31% of coots moving among wetlands, and very high levels of daily movement in stilts. A network analysis revealed strong evidence for fidelity among individual stilts to specific wetlands, indicating different groups of wetlands supported different birds. There was also strong evidence for patterns in daily and seasonal movement patterns of stilts. Our work indicates the importance of each wetland to the waterbirds they support, as each individual had strong fidelity to a single wetland. In addition, for Hawaiian coots and stilts, which were documented moving among multiple wetlands, a network of wetlands may be key for long‐term persistence of these endangered species, and coordinated regional management of waterbirds as a shared resource could provide greater benefits to waterbirds than independent management of each wetland. We established an automated radio‐telemetry tracking network to document multi‐year movement of 3 endangered waterbirds, ʻalae ʻula (Hawaiian gallinule), ʻalae keʻokeʻo (Hawaiian coot), and aeʻo (Hawaiian stilt), among wetlands on Oʻahu, Hawaiʻi. We found significant differences in the movement propensity of the 3 species, with no movement among sites detected in ʻalae ʻula, 31% of individuals of ʻalae keʻokeʻo moving among wetlands, and very high levels of daily movement in aeʻo. All 3 species, even the mobile aeʻo showed strong fidelity to a single wetland.
Charles van Rees
added a research item
The study of island subspecies provides excellent “natural experiments” for examining the impacts of different selective regimes on animal taxa. We examined the morphological differences between the Hawaiian and continental North American subspecies of the Common Gallinule (Gallinula galeata sandvicensis and G. g. cachinnans, respectively), for which the existing literature is both scant and contradictory. More than 200 live gallinules and >100 museum specimens were measured, and a meta-analysis of literature values on North American Common Gallinules was conducted to quantitatively assess differences in wing chord, culmen and tarsus length, and body mass between these subspecies. Hawaiian Common Gallinules had smaller wing chords (–2.5 to –4.0%), larger culmen (+4.5 to +7.0%) and tarsi (+5.5 to +23.0%), and slightly larger body masses (∼+4.0%) than their mainland conspecifics. This is likely due to several factors including reduced predation pressure, shorter dispersal distances, nonmigratory behavior, and sedentary lifestyles associated with ecological differences between the Hawaiian Islands and the North American mainland. We also introduce the novel hypothesis that intra- and interspecific agonistic interactions due to habitat limitation are an additional selective force in driving these morphological changes.
Charles van Rees
added a research item
Physiological metrics are becoming popular tools for assessing individual condition and population health to inform wildlife management and conservation decisions. Corticosterone assays can provide information on how animals cope with individual and habitat-level stressors, and the recent development of feather assays is an exciting innovation that could yield important insights for conservation of wild birds. Due to the widespread enthusiasm for feather corticosterone as a potential bioindicator, studies are needed to assess the ability of this technique to detect meaningful differences in physiological stress across a variety of stressor types and intensities. We examined feather corticosterone from 144 individuals among the 13 known breeding populations of Hawaiian gallinule (Gallinula galeata sandvicensis), an endangered waterbird, on the island of O'ahu. These ecologically independent subpopulations are known to have low genetic connectivity and movement rates and differ largely across a number of important conditions, including level of predator management, human disturbance, proximity to urban development and conspecific population density. This system is well suited for assessing the performance of feather corticosterone as a bioindicator of different known habitat-level threats common to this and many other conservation-reliant species. We found no statistically significant relationship between feather corticosterone and level of predator control, level of human disturbance, gallinule population density, percent urban cover or body condition across all sites despite the substantial difference in stressor magnitude in our dataset. We did find that gallinules in habitats with larger population densities were in worse body condition. These findings suggest that feather corticosterone is not a consistent indicator of anthropogenic impacts on populations. Furthermore, they suggest that feather corticosterone may be a poor bioindicator of known habitat-level threats for Hawaiian gallinules and that it should be used with caution in other avian taxa of conservation concern.
Charles van Rees
added 2 research items
Wetlands represent a unique and important part of Hawai‘ i’s ecological and cultural history, mediating the interactions of terrestrial and marine ecosystems and providing diverse food and other resources to traditional societies. Wetland loss and degradation on the Hawaiian Islands have been severe since European colonization and subsequent landscape change has altered the interactions of terrestrial and offshore marine ecosystems, with negative impacts of cultural and economic importance. Wetland conservation and restoration may be key to reducing these impacts as well as adapting Hawai‘i’s cities to future climate change. Unfortunately, public interest in wetland conservation appears limited compared to that in other ecosystems like coral reefs and forests. I propose that the conservation profile of Hawaiian wetlands could be increased using flagship species, and that Hawai‘i’s endemic waterbirds, especially the ‘Alae ‘ula (Hawaiian gallinule, Gallinula galeata sandvicensis, formerly G. chloropus sandvicensis), Ae‘o (Hawaiian stilt, Himantopus mexicanus knudsenii), and ‘Alae ke‘o ke‘o (Hawaiian coot, Fulica alai) are excellent candidate species because of their endemism, identifiability, accessibility for viewing, and cultural connections with traditional Hawai‘i. Such flagship species could contribute to building a movement for wetland conservation in Hawai‘i, which in turn has major implications for climate adaptation and the health of marine coastal systems in the state.
Anthropogenic alterations to landscape structure and composition can have significant impacts on biodiversity, potentially leading to species extinctions. Population‐level impacts of landscape change are mediated by animal behaviors, in particular dispersal behavior. Little is known about the dispersal habits of rails (Rallidae) due to their cryptic behavior and tendency to occupy densely vegetated habitats. The effects of landscape structure on the movement behavior of waterbirds in general are poorly studied due to their reputation for having high dispersal abilities. We used a landscape genetic approach to test hypotheses of landscape effects on dispersal behavior of the Hawaiian gallinule (Gallinula galeata sandvicensis), an endangered subspecies endemic to the Hawaiian Islands. We created a suite of alternative resistance surfaces representing biologically plausible a priori hypotheses of how gallinules might navigate the landscape matrix and ranked these surfaces by their ability to explain observed patterns in genetic distance among 12 populations on the island of O`ahu. We modeled effective distance among wetland locations on all surfaces using both cumulative least‐cost‐path and resistance‐distance approaches and evaluated relative model performance using Mantel tests, a causal modeling approach, and the mixed‐model maximum‐likelihood population‐effects framework. Across all genetic markers, simulation methods, and model comparison metrics, surfaces that treated linear water features like streams, ditches, and canals as corridors for gallinule movement outperformed all other models. This is the first landscape genetic study on the movement behavior of any waterbird species to our knowledge. Our results indicate that lotic water features, including drainage infrastructure previously thought to be of minimal habitat value, contribute to habitat connectivity in this listed subspecies.
Charles van Rees
added a research item
We conducted a spatially explicit, stochastic, individually based population viability analysis for the Hawaiian common gallinule (Gallinula galeata sandvicensis), an endangered subspecies of waterbird endemic to fragmented coastal wetlands in Hawai'i. This subspecies persists on two islands, with no apparent movement between them. We assessed extirpation risk for birds on O'ahu, where the resident gallinule population is made up of several fragmented subpopulations. Data on genetic differentiation were used to delineate subpopulations and estimate dispersal rates between them. We used sensitivity analyses to gauge the impact of current uncertainty of vital rate parameters on population projections, to ascertain the relative importance of gallinule vital rates to population persistence, and to compare the efficacy of potential management strategies. We used available sea level rise projections to examine the relative vulnerability of O'ahu's gallinule population to habitat loss arising from this threat. Our model predicted persistence of the island's gallinule population at 160 years (∼40 generations), but with high probabilities of extirpation for small subpopulations. Sensitivity analyses highlighted the importance of juvenile and adult mortality to population persistence in Hawaiian gallinules, justifying current predator control efforts and suggesting the need for additional research on chick and fledgling survival. Subpopulation connectivity from dispersal had little effect on the persistence of the island-wide population, but strong effects on the persistence of smaller subpopulations. Our model also predicted island-wide population persistence under predicted sea level rise scenarios, but with O'ahu's largest gallinule populations losing >40% of current carrying capacity.
Charles van Rees
added a research item
Contributing to conservation and management of endangered Hawaiian waterbirds by identifying important wetlands, flight pathways, and critical dispersal barriers that influence the overall population connectivity and extinction risk of three endemic Hawaiian waterbirds. This information will promote stewardship by allowing landowners to work cooperatively towards the recovery of these endangered biologically and culturally significant Hawaiian bird species. Link to Poster: http://iucncongress.ipostersessions.com/?s=37-9F-D5-78-E8-F9-A0-75-9F-5F-26-99-E3-AE-E3-2C
Charles van Rees
added a research item
Vital rates describe the demographic traits of organisms and are an essential resource for wildlife managers to assess local resource conditions and to set objectives for and evaluate management actions. Endangered waterbirds on the Hawaiian Islands have been managed intensively at state and federal refuges since the 1970s, but with little quantitative research on their life history. Information on the vital rates of these taxa is needed to assess the efficacy of different management strategies and to target parts of the life cycle that may be limiting their recovery. Here we present the most comprehensive data to date on the vital rates (reproduction and survival) of the Hawaiian gallinule (Gallinula galeata sandvicensis), a behaviorally cryptic, endangered subspecies of wetland bird endemic to the Hawaiian Islands that is now found only on Kaua'i and O'ahu. We review unpublished reproduction data for 252 nests observed between 1979 and 2014, and assess a database of 1620 sightings of 423 individually color-banded birds between 2004 and 2017. From the resighting data, we estimated annual apparent survival at two managed wetlands on O'ahu using Cormack-Jolly-Seber models in program MARK. We found that Hawaiian gallinules have smaller mean clutch sizes than do other species in the genus Gallinula, and that clutch sizes on Kaua'i are larger than those on O'ahu. The longest-lived bird in our dataset was recovered dead at age 7 years, 8 months, and the youngest confirmed age at first breeding was 1 year 11 months. In four years of monitoring 14 wetland sites, we confirmed three inter-wetland movements on O'ahu. In our pooled dataset, we found no statistically significant differences between managed and unmanaged wetlands in clutch size or reproductive success, but acknowledge that there were limited data from unmanaged wetlands. Our best supported survival models estimated an overall annual apparent survival of 0.663 (95% CI 0.572-0.759); detection varied across wetlands and study years. First-year survival is a key missing component in our understanding of the demography of Hawaiian gallinules. These data provide the foundation for quantitative management and assessment of extinction risk of this endangered subspecies.
Charles van Rees
added a research item
The effects of anthropogenic landscape change on genetic population structure are well studied, but the temporal and spatial scales at which genetic structure can develop, especially in taxa with high dispersal capabilities like birds, are less well understood. We investigated population structure in the Hawaiian gallinule (Gallinula galeata sandvicensis), an endangered wetland specialist bird on the island of O`ahu (Hawai`i, USA). Hawaiian gallinules have experienced a gradual population recovery from near extinction in the 1950s, and have recolonized wetlands on O`ahu in the context of a rapidly urbanizing landscape. We genotyped 152 Hawaiian gallinules at 12 microsatellite loci and sequenced a 520 base-pair fragment of the ND2 region of mitochondrial DNA (mtDNA) from individuals captured at 13 wetland locations on O`ahu in 2014–2016. We observed moderate to high genetic structuring (overall microsatellite FST = 0.098, mtDNA FST = 0.248) among populations of Hawaiian gallinules occupying wetlands at very close geographic proximity (e.g., 1.5–55 km). Asymmetry in gene flow estimates suggests that Hawaiian gallinules may have persisted in 2–3 strongholds which served as source populations that recolonized more recently restored habitats currently supporting large numbers of birds. Our results highlight that genetic structure can develop in taxa that are expanding their range after severe population decline, and that biologically significant structuring can occur over small geographic distances, even in avian taxa.
Charles van Rees
added a project goal
Integrating population genetics, landscape genetics, radio telemetry, and mark-resight studies to understand the impacts of anthropogenic landscape change on the movement behavior and population structure of an endangered Hawaiian waterbird. Comparing commonly used field methods for estimating movement, and statistical methods for estimating functional and structural population connectivity.