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Laysan duck

The Laysan duck (Anas laysanensis) formerly occurred throughout the Hawaiian islands. By the late 19th century it was known only from Laysan Island and Lisianski Island [1]. The cause of its extirpation from the majority of the Hawaiian islands is unknown, but is presumed to have been induced by Polynesian colonizers and the mammalian predators, such as rats, that they brought with them. In 2004 and 2005, the species was reintroduced to the Midway Atoll National Wildlife Refuge. Over 200 ducks exist in captivity, but are not suitable for reintroduction.

The Laysan duck was first reported on Lisianski Island in 1828. Its fortune changed for the worse in 1844 when shipwrecked sailors washed ashore, eating the duck and other native species to survive [1]. Of greater long-term impact, however, was the accidental introduction of mice (Mus musculus) to the island later that year by a rescue ship. A second shipwreck party washed ashore in 1846. By 1857 mice had denuded the island, destroying the duck's habitat. By 1916 the mouse and rabbit population starved to death due to lack of vegetation [1]. Unencumbered by vegetation, windblown sand filled in the island's freshwater springs. The Laysan duck was extirpated from Lisianski some time between 1845 and 1857.

The pre-exploitation population size on Laysan Island is not known but was described as "not very plentiful" in the winter of 1891 [1]. It was presumably larger than the current carrying capacity of about 500 birds because the extent of current habitat is known to be smaller than in the pre-exploitation period [2]. Laysan did not experience sustained human disturbance and was not colonized by humans until guano miners occupied it from 1891 to 1904 [5]. Within six months of arriving, they killed 300,000 nesting seabirds for food and sport. Their greatest impact, however, was the introduction of European rabbits (Oryctolagus cuniculus) which thoroughly denuded the island by the 1910s, reducing hiding cover and prey habitat, and allowing windblown sand to bury freshwater springs and reduce the size of the island's central hypersaline lake [4]. The extinction of 14 species including the Laysan rail, Laysan honeycreeper and Laysan millerbird have been linked to the rabbit invasion [3]. Laysan was made part of the Hawaiian Islands Bird Reservation in 1909, but was not policed, allowing Japanese feather hunters scoured it in 1909 and 1910, killing Laysan ducks for food and feathers. The species was nearly driven to extinction, being reduced to less than 100 birds in 1902 and just 7 adults in 1911 and 1912 [1].

Rabbit eradication efforts were unsuccessful in 1912 and 1913, but having denuded the island, the species starved to death by 1923 [5]. Laysan duck numbers slowly increased as the vegetation grew back, allowing the species to increase to about 500 birds by 1957 [1]. Intermittent surveys suggest that the species maintained a population of 400-600 birds from 1957 to 2005, with the exception of a dramatic population crash in late 1993 and early 1994 due to sustained drought [1]. The population grew steadily from the 1994 low point back to about 500 birds in 2004 [1].

In 1967, 12 birds were relocated to Southeast Island on Pearl and Hermes Reef, but were not seen in subsequent years. Twenty ducks were translocated to Midway Atoll National Wildlife Refuge in October, 2004 [2]. Nineteen birds, including six females were still alive in September, 2005. Five of the six females nested, fledging seven duckling; four more birds may fledge by the end of the season [2]. Sixteen additional birds were released on Eastern Island and six on Sand Island in October 2005 [2]. During 2005, 12 ducklings successfully fledged on Sand Island, 11 of which survived as of January, 2006. The total Midway duck population as of January, 2006 was 51: 18 survivors from the 2004 release, 22 survivors from 2005 release, and 11 successful fledglings.

In the late 1950s, 33 birds were taken from Laysan into captivity [1]. Their offspring and seven additional wild birds were use to establish a colony at the Pohakuloa Endangered Species Facility on the Island of Hawai`i, but the colony proved unsuitable for reintroduction purposes. Captive breeding efforts ceased in Hawaii in 1989. As of 1999, 211 birds descended from 19 founders existed in 32 facilities worldwide [1]. While initially successful, captive breeding programs have experienced difficulties in recent years. While future conservation efforts in Hawaii may include establishing semi-wild populations, they are not expected to utilize any birds currently in captivity.

[1] U.S. Fish and Wildlife Service. 2004. Draft Revised Recovery Plan for the Laysan Duck (Anas laysanensis). U.S. Fish and Wildlife Service, Portland, Oregon. vii + 94 pp.
[2] Klavitter. 2006. Personal communication with John Klavitter, U.S. Fish and Wildlife Service, Midway Atoll National Wildlife Refuge, January 16, 2006.
[3] Center for Biological Diversity. 2005. Database of Extinct, Endangered and Vulnerable Species. Center for Biological Diversity, Tucson, AZ.
[4] Moulton, D. W., and A. P. Marshall. 1996. Laysan Duck (Anas laysanensis). In The Birds of North America, No. 242 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists’ Union, Washington, D.C.

Banner photo © Phillip Colla