WatchList Species Account for Nihoa Millerbird
(Acrocephalus familiaris)

Qualifies for the list as a Red List Species


Nihoa Millerbird
Photo: Jack Jeffrey

Both the Nihoa and Laysan Millerbirds are regarded as subspecies. The Laysan Millerbird became extinct around 1923 as a result of introduced European rabbit’s depredations on the vegetation of Laysan Island. The Nihoa form is endemic to the steep, rocky island of Nihoa, only 156 acres in size, and 900 feet above the ocean. The island, partially covered with low, scrubby vegetation, is located in the Northwestern Hawaiian Islands National Wildlife Refuge.


Nihoa can be visited only with access permits. There are steep cliffs on three of the island’s four sides, making landing there difficult. Save for yearly population estimates by U.S. Fish and Wildlife biologists, the Nihoa Millerbird has not been the subject of any systematic studies.


Population estimates for this species have ranged from 31 to 731, since the 1960s, with an average of 381 birds; no long-term trends are evident.


The Millerbird is found in all the vegetated portions of the island, where it gleans insects from shrubs, bunchgrass, and other vegetation. Some observers have noticed that the Millerbird seems to prefer habitats near the few freshwater seeps on the island. Even on this small island, the birds are apparently very sedentary and probably remain on the same half-acre to one-acre territories for their entire lives.


The Nihoa Finch, the only other passerine on the island, may sometimes eat Millerbird eggs; severe drought or storms also create population bottlenecks for the bird. Unauthorized boat landings and the further introduction of alien plants and animals also pose significant threats. Several alien species of plants and insects are already established on the island..


Though Nihoa Millerbirds have never been translocated , there is discussion of replacing the extinct Laysan Millerbird with Nihoan Millerbirds on Laysan Island. If translocation is attempted, it should only use birds of the year, and only during high population years, so the Nihoa population is not jeopardized.