Nihoa Millerbird translocation from Nihoa to Laysan, Northwestern Hawaiian Islands, USA

Summary

The Nihoa Millerbird (Acrocephalus familiaris kingi), Critically Endangered and confined to the tiny 72-hectare island of Nihoa in the Northwestern Hawaiian Islands after a related subspecies went extinct on Laysan by 1923, was translocated to re-establish the genus on Laysan as insurance against a single-island population's vulnerability. A coalition led by the US Fish and Wildlife Service and American Bird Conservancy spent years confirming Laysan's habitat and insect prey base had recovered enough to support the birds, developing field sexing techniques and avicultural methods through 2009-2010 captive trials to keep small, energetic birds healthy through an eight-day voyage, and securing a dedicated chartered vessel given the remoteness and archaeological sensitivity of both islands. In 2011 and 2012, within a narrow weather window further restricted to avoid dependent young, 50 Millerbirds were captured on Nihoa and translocated to Laysan in two cohorts. Post-release monitoring using VHF transmitters and color bands found one-year survival of 58% for the 2011 cohort and 96% for the 2012 cohort, with the first successful nest recorded around six months after the initial release; by September 2014, the combined wild and translocated population reached a minimum estimate of 164 birds, with breeding territories climbing from 11 in 2011 to 75 in 2014. Major difficulties included Nihoa's extreme access restrictions and expense, year-to-year funding uncertainty, and the 2013 closure of Laysan's long-running field camp, which curtailed continuous monitoring. The project rates itself successful, crediting years of dedicated background research, a distinguished multi-agency and Native Hawaiian partnership, and the species' inherent toughness and adaptability.