Potential Impact of Mammalian Nest Predators on Endemic Forest Birds of Western Mauna Kea, Hawaii

Abstract

I used dummy nest experiments to investigate the role of nest predation by introduced mammals asa significant limiting factor for the endangered Palila (Loxioides bailleui) and other endemic birds on the western slope of Mauna Kea. Overall predation rates on dummy nests were extremely low. Rates were comparable to those on actual Palila nests, indicating that dummy nests give a valid representation of the dynamics of nest predation. The black rat (Rattus rattus) was the only important predator. Feral cats (Felis catus) played only a minor role, and there was no evidence to implicate house mice (Mus musculus) as nest predators. Four factors appear to be responsible for the low nest predation rates: (1) only a single species of predator (black rat) is involved; (2) rat densities are extremely low on Mauna Kea; (3) low prey (nest)densities preclude density‐dependent predation, and (4) rats have alternative foods that are more abundant and accessible than arboreal bird nests. Since mammalian predation appears unlikely to have a significant impact on the Palila, other factors must be limiting the abundance of this endangered species.