Differential impacts of native and non-native predators on the nesting success of Hawaiian stilts (Himantopus mexicanus knudseni)

Context Predation is a leading cause of reproductive failure among ground-nesting birds, particularly in island ecosystems in which invasive predators have disrupted historical community interactions. The Hawaiian stilt (Aeʻo – Himantopus mexicanus knudseni), endemic to the Hawaiian Islands, is vulnerable to a diverse suite of predators that could impact nesting success. Aims To determine the relative impact of native and invasive predator species, and nest-site characteristics (vegetation height, distance to interior road, distance to water), on Hawaiian stilt nesting success. Methods Field surveys and motion-activated cameras were used to assess the impacts of nest-site characteristics and predators on nesting success of Hawaiian stilts. Key results The presence of invasive mammals – especially cats, mongooses, and rats – was significantly associated with nest failure, accounting for most confirmed predation events. The native black-crowned night heron (ʻaukuʻu – Nycticorax nycticorax hoactli) was also detected at nests and contributed substantially to predation events. Nests with shorter vegetation within a 1-m radius were more likely to be visited by mammalian predators and more likely to be predated. Conclusions Prior to this study, the relative contributions of predators from various taxonomic groups on Hawaiian waterbird nest failure were poorly understood. Our findings underscore the disproportionately high impact of invasive mammals on Hawaiian stilt nesting success. Implications Our results support mammal exclusion fencing and eradication efforts as critical components of conservation strategies for ground-nesting waterbirds in the Hawaiian Islands.