NEST SITE SELECTION AND PREDATOR IMPACTS ON THE REPRODUCTIVE SUCCESS OF THREE ENDANGERED WATERBIRDS IN HAWAIʻI.
Date
2024
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Abstract
Precocial species leave the nest soon after hatching, making them vulnerable to a variety of threats as they search for food and shelter prior to gaining the ability to fly. Adaptive habitat-selection theory suggests that animals should select areas with habitat characteristics that maximize fitness, so species with precocial chicks should select nesting areas with characteristics that maximize success during both the egg and chick stages. Recent studies suggest that endangered species recovery may be hampered when predator impacts differ between nest and chick stages, requiring different management strategies to protect across the reproductive stages. Predation of the egg and chick stages are a major cause of reproductive failure in three endangered Hawaiian waterbirds, the Ae‘o (Hawaiian Stilt; Himantopus mexicanus knudseni), the ‘Alae ke‘oke‘o (Hawaiian Coot), and ‘Alae ‘ula (Hawaiian Gallinule; Gallinula galeata sandvicensis), but predator types likely differ between stages, making them an ideal species in which to examine relationships between nest-site selection, predator types, nesting and fledging success. In this study, we utilized motion-activated game cameras at nests and tracking of chicks to evaluate: (1) which nest-site characteristics are related to egg predation by different species; and (2) the relationship between habitat characteristics, predator detections at the nest, and fledging success. (3) which nest-site characteristics and predator detections at nest are related to chick survival by different species; and (4) what is the relationship between predator detections and nest site characteristics with chick fate by the two Hawaiian waterbird species. Using a linear and binomial logistic regression and exposure models, we found that nest concealment of vegetation (vegetation density) was not a predictor for predation risk at both the nest and chick stages. We found a 5% increase in stilt chick survival over the nesting season and a 5% decrease in gallinule chick survival over the nesting season, suggesting seasonal changes in food abundance or predation risk. ‘Alae ‘ula chicks were detected in American Bullfrog stomachs, confirming them as a source of chick, but not egg, mortality. Based on our results, management actions aimed at improving nesting success will not simultaneously improve chick survival, with the exception of the removal of mammals, which benefits both. A critical need to improve outcomes for chicks is the development of better control options for invasive reptiles, amphibians, and invertebrates.
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Natural resource management
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91 pages
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