The O'ahu ‘Elepaio (Chasiempis sandwichensis ibidis) is an endangered monarch flycatcher endemic to the Hawaiian Island of O'ahu. One of the main causes of the decline of this forest bird is low nest success. This study investigated whether introduced rodents might be important nest predators in ‘Elepaio habitat by conducting artificial nest experiments before and during a rodent control program. In each experiment, 20 artificial nests with two quail eggs each were placed on the ground and in trees, then checked at 5, 10, and 15 day intervals. The size, appearance, location, and odor of artificial nests were considered in order to make the experiment more realistic. Rodent control decreased predation on artificial tree and ground nests by 45% and 55%, respectively. Predation on ground nests was higher than predation on tree nests before rodent control, but afterwards predation was low on both ground and tree nests and did not differ between them. Survival of artificial tree nests after rodent control (80%, 0.985 daily) was similar to survival through incubation of ‘Elepaio nests (82%, 0.989 daily), indicating the artificial nests provided a realistic measure of predation on ‘Elepaio nests. Automatic cameras wired to nests documented the identity of the predator in 10 events; in every case it was a black rat (Rattus rattus). Black rats appear to be the primary nest predator in O'ahu ‘Elepaio habitat, and rodent control is a valuable management technique that can be used to increase the reproductive success of ‘Elepaio.