Nest depredation risk increases later in the nesting season for a subtropical wading bird, the Hawaiian Stilt (Himantopus mexicanus knudseni)

Nest depredation is the leading cause of nest failure in avian species. While depredation risk largely depends on depredation pressure, it may also be influenced by the timing of the nesting season and by nest site features, such as proximity to water and vegetation height. The Hawaiian Stilt (Himantopus mexicanus knudseni) is an endangered Hawaiian waterbird that nests in wetlands across the Hawaiian Islands from February to September. The nesting season coincides with a seasonal decline in precipitation, which may impact depredation rates. In this study, we used observational surveys and nest cameras to examine the impact of nest-site characteristics and nest initiation date on nest depredation of the Hawaiian Stilt. We found that stilts preferred shorter vegetation than what was randomly available and preferred to nest in Pickleweed (Batis maritima) rather than other available plant species. However, nest-site characteristics, such as vegetation height and distance to water, did not have an impact on depredation risk. Early nests had a higher chance of survival than late nests. The number of depredated nests peaked later in the nesting season, and introduced mammals were the primary nest predators. Increasing invasive predator control later in the Hawaiian Stilt nesting season, particularly for mammalian predators, may increase nest survival of later nesters. Our study is the first to examine seasonality in nest depredation of Hawaiian Stilts and suggests that, despite longer nesting seasons and year-round occupation of wetlands, late nesters in subtropical regions may have greater depredation risk than early nesters, similar to trends observed in temperate regions.
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