PS 49-268 - CANCELLED - Nest site selection and predator impacts on the reproductive success of two endangered waterbirds in Hawai‘i.

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. Yet few studies have evaluated the effects of nest-site selection on both egg and chick success, in part because of the challenges associated with tracking chicks after they leave the nest. Recent studies suggest that endangered species recovery may be hampered by these knowledge gaps, particularly when predator impacts differ between nest and chick stages. Predation at the egg and chick stages is a major cause of reproductive failure in two endangered Hawaiian waterbirds, the Ae‘o (Hawaiian Stilt; Himantopus mexicanus knudseni) and ‘Alae ‘ula (Hawaiian Gallinule; Gallinula galeata sandvicensis) populations, but predator types likely differ between stages, making them an ideal species in which to examine relationships between nest-site selection, predator types, hatching success, and fledging success. In this study we utilized motion-activated game cameras at nests and VHF 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. Vegetation height and the detection of mammals at the nest were both highly predictive of hatching success and fledging success. ‘Alae ‘ula chicks were detected in American Bullfrog stomachs, confirming them as a source of chick, but not egg, mortality. Our results will inform targeted removal of high-impact predators during each life history stage. Innovations in amphibian removal, along with predator-free fencing are likely critical to improving chick survival.