Non-native Mammalian Predator Control to Benefit Endangered Hawaiian Waterbirds

Abstract

Hawai‘i’s wetlands are inhabited by 5 endangered endemic waterbird species: the Hawaiian stilt (ae‘o), Hawaiian coot (‘alae ke‘oke‘o), Hawaiian duck (koloa maoli), Hawaiian goose (nēnē), and Hawaiian gallinule/Moorhen (‘alae ‘ula). One of the biggest threats facing these waterbirds is predation by non-native mammalian predators. Non-native cats, rats, and mongooses all directly depredate either eggs, young, or adult birds. Control of these predators is a key component of the active management strategy employed to recover Hawaiian waterbirds. Predator control efforts have included live or kill traps, rodenticide bait stations, and fences in areas important for the waterbirds. To evaluate the success of these predator control efforts on key wetland national wildlife refuges in Hawai‘i, we explored 4 metrics: live trap capture history, rodent and mongoose presence/absence using track tunnels, waterbird population densities, and waterbird reproductive success. The track tunnel data documented lower predator density within the predator control areas. The live trapping capture history data showed strong spatial patterns of higher success along perimeter fence lines and limited success within the interior of the wetlands. We also found that areas receiving predator control had both higher reproductive success and, in most cases, greater waterbird population densities. These findings support mammalian predator control as a key management strategy to promote recovery of these endangered species.