Non-native mammalian predator control to benefit endangered Hawaiian waterbirds

Background/Question/Methods

Hawai‘i’s wetlands are inhabited by five endangered endemic waterbird species, the Hawaiian Coot (‘alae ke‘oke‘o), Hawaiian Duck (koloa maoli), Hawaiian Stilt (ae‘o), Hawaiian Gallinule (Moorhen) (‘alae ‘ula), and Hawaiian Goose (nēnē).  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 these Hawaiian waterbirds. Predator control efforts have included live or kill traps, rodenticide baited stations, and fences in areas important for the waterbirds. To evaluate the success of these predator control efforts on key Hawaiian wetland National Wildlife Refuges, we explored four metrics: live-trapping capture history, rodent and mongoose presence/absence using track tunnels, waterbird population counts, and waterbird nest success.

Results/Conclusions

The track tunnel data documented lower predator density within the predator control areas. The trapping capture history data showed strong spatial patterns of higher success along fence lines and limited success within the core of the wetlands. We also found that in the areas evaluated, those receiving predator control had both higher nest success and in most cases greater waterbird population densities. These finding corroborate the importance of predator control as a key piece of the management strategy for these endangered species.