Millerbird Acrocephalus familiaris Scientific name definitions

The Nihoa Millerbird and Laysan Millerbird are the only known Old World warblers (subfamily Sylviinae) that colonized the Hawaiian Archipelago, the most remote group of islands in the world. The Laysan form, discovered first, was named “millerbird” (Henshaw 1902a Henshaw, H. W. (1902a). Birds of the Hawaiian Islands being a complete list of the birds of the Hawaiian possessions with notes on their habits. Honolulu, HI: Thomas G. Thrum. Close ) because of its fondness for feeding on large miller moths (Family Noctuidae: probably Agrotis spp.). The Laysan and the Nihoa millerbirds are generally regarded as (at least) separate subspecies.

The extant Nihoa form is endemic to the tiny (63 ha; 40 ha vegetated) island of Nihoa, and the now extinct Laysan Millerbird was endemic to Laysan Island (407 ha; 187 ha vegetated), approximately 1,060 km to the northwest of Nihoa (U.S. Fish and Wildlife Service 1984d Fish, U.S. and Wildlife Service. (1984d). Recovery plan for the Northwestern Hawaiian Islands passerines. Portland, OR: U.S. Fish and Wildl. Serv. Close , Conant 1985a Conant, S. (1985a). Recent observations on the plants of Nihoa Island, Northwestern Hawaiian Islands. Pacific Science 39 (2):135-149. Close , Morin and Conant 1994 Morin, M. P. and S. Conant. (1994). Variables influencing population estimates of an endangered passerine. Biological Conservation 67:73-84. Close ). The Nihoa Millerbird was discovered in 1923, in the same year that the Laysan subspecies was concluded to be extinct (Wetmore 1923 in Olson 1996a Olson, S. L. (1996a). History and ornithological journals of the Tanager Expedition of 1923 to the Northwestern Hawaiian Islands, Johnston and Wake Islands. Atoll Research Bulletin 433:1–210. Close ). There is no evidence that this genus ever occurred elsewhere in the Hawaiian Archipelago (Olson and Ziegler 1995 Olson, S. L. and A. C. Ziegler. (1995). Remains of land birds from Lisianski Island, with observations on the terrestrial avifauna of the Northwestern Hawaiian Islands. Pacific Science 49 (2):111-125. Close ).

Both forms are generally characterized as small and drab. Observers frequently describe them as highly active, which can be explained by their insect foraging habits.

Although first described only in 1892 (Rothschild 1892b Rothschild, W. (1892). Descriptions of seven new species of birds from the Sandwich Islands. The Annals and Magazine of Natural History, series 6 10 (55):108–112. Close ), the Laysan Millerbird became extinct between 1916 and 1923 (Ely and Clapp 1973 Ely, C. A. and R. B. Clapp. (1973). The natural history of Laysan Island Northwestern Hawaiian Islands. Atoll Research Bulletin 171. Close , Sincock and Kridler 1977 Sincock, J. L. and E. Kridler. (1977). The extinct and endangered endemic birds of the Northwestern Hawaiian Islands. Honolulu, HI: Unpubl. manuscript, U.S. Fish and Wildl. Serv. Close , Sincock 1979 Sincock, J. L. (1979). A proposal to transplant the Nihoa Millerbird and Nihoa Finch to increase their survival potential. Laurel, MD: U.S. Fish and Wildlife Service, Patuxent Wildlife Res. Center. Close ). Minimal information exists on the Laysan Millerbird, since few naturalists observed this species in life (Fisher Fisher 1903b Fisher, W. K. (1903b). Birds of Laysan and the leeward islands, Hawaiian Group. U.S. Fish. Comm. Bull. 23 (pt. 3):767-807. Close , Fisher 1903c Fisher, W. K. (1903c). Notes on the birds peculiar to Laysan Island, Hawaiian group. Auk 20 (4):384-397. Close , Bailey 1956a Bailey, A. M. (1956a). Birds of Midway and Laysan islands. Denver Mus. Nat. Hist. Mus. Pict. 12. Close ).

The Laysan Millerbird's extinction, along with a host of other endemic species' extinctions, was ultimately caused by the introduction of Old World rabbits (Oryctolagus cuniculus) on Laysan in approximately 1903. With no terrestrial mammalian predators present, the rabbit population exploded and denuded Laysan of vegetation (Bailey 1956a Bailey, A. M. (1956a). Birds of Midway and Laysan islands. Denver Mus. Nat. Hist. Mus. Pict. 12. Close , Ely and Clapp 1973 Ely, C. A. and R. B. Clapp. (1973). The natural history of Laysan Island Northwestern Hawaiian Islands. Atoll Research Bulletin 171. Close ).

Access to the Nihoa Millerbird is limited not only by the remoteness of Nihoa Island and required access permits, but also by the difficulty of landing on this steep, rocky island, often surrounded by rough seas. Although this endangered species has been somewhat protected by limited and difficult access, these restrictions also have limited research on its natural history. Aside from almost yearly population estimates made by U.S. Fish and Wildlife Service refuge biologists during brief visits, most information about millerbird natural history is anecdotal and based on short visits made in the 1960s and 1970s (Sincock and Kridler 1977 Sincock, J. L. and E. Kridler. (1977). The extinct and endangered endemic birds of the Northwestern Hawaiian Islands. Honolulu, HI: Unpubl. manuscript, U.S. Fish and Wildl. Serv. Close ) and early 1980s (SC). Research is also curtailed by justifiable concerns about the negative impact of even minimal human activities on the seabird colonies of Nihoa I., as well as its numerous endemic plants and invertebrates.