Laysan Duck
(Anas laysanensis)

The Laysan Duck, Anas laysanensis, has the most restricted range of any duck species, and is especially vulnerable to extinction because of its small population size. Laysan Island, part of the Northwestern Hawaiian Islands National Wildlife Refuge is the last refugia of this endangered species. These unique birds were formerly believed to be endemic to Laysan, until new evidence revealed Laysan Ducks were previously common and widespread in the Hawaiian archipelago. Important background information on ecosystem parameters, foraging, diet, and population dynamics is critical to management of this endangered species. This report summarizes 1998 to 1999 preliminary data from field studies on Laysan and on captive Laysan Ducks.

The Laysan Duck Recovery Plan (USFWS 1982) recommends evaluating "reintroduction" sites after the evaluation of field data. The need for this information has been identified by the USFWS Remote Island Team, USFWS Refuge biologists and managers, the USGS-BRD Pacific Islands Ecosystems Research Center, the Laysan Duck Recovery Plan (USFWS 1982), and Ducks Unlimited, Inc.

The USFWS initiated cooperative field studies in 1998 to improve population-monitoring techniques and examine poorly understood aspects of the duck's ecology to benefit recovery planning. The wild population of Laysan Ducks is approximately 322 (plus or minus 33) adults (1999 USGS data). Population monitoring from 1991 to 1999 suggests that droughts during periods of high population density are correlated with population crashes (USFWS data). In periods of lower population densities on Laysan, drought conditions resulted in poor reproductive success and recruitment (1998 USGS USFWS unpub. data). Despite a good breeding year in 1999, field studies indicate that the population growth appears to be limited by duckling survival (1998 to 1999 USGS unpub. data). Causes for high duckling mortality will be examined in the year 2000 breeding season.

Field studies indicate that the ducks have a varied diet, flexible foraging behaviors, and seasonal food shifts. Ducks spent more time foraging and foraged more on terrestrial invertebrates during dry conditions on Laysan in 1998. Terrestrial invertebrates are essential components of the duck's foraging ecology, especially during periods of drought when the wetland invertebrates are less abundant (USGS data). The survival of Laysan Ducks in the wild is dependent on the absence of introduced predators, competitors, and diseases.

Data suggest that the Laysan Duck's wide range of foraging behaviors is favorable to establishing the birds on additional islands. Laysan Ducks could utilize a restored environment with a variety of foraging substrates and prey items. We recommend fledged juveniles as the best candidates for wild translocation, and wild egg removal for establishment of a new captive flock in Hawaii to produce birds for release. The existing captive Laysan Duck stock is unsuitable for release into the wild. We also provide an evaluation of select translocation sites, and recommend necessary habitat restoration for translocation sites. We describe aspects of the duck's ecology and the range of resources (invertebrate prey, water, vegetation, and predators) under which successful translocation is possible, and predict suitability of potential release sites with respect to these resources. Of Hawaii's predator-free islands, Midway Atoll, Lisianski Island, Nihoa and Kure had the highest potential for habitat restoration and the establishment of additional Laysan Duck populations.

Timing translocation according to the population dynamics on Laysan is essential. Removal of birds during a population high point will prevent or reduce any negative impacts to the Laysan population. Post release monitoring and restoration efforts for release sites are required for establishment of new self-sustaining or minimally managed populations. Freshwater seep restoration or wetland creation, vegetative cover, absence of mammalian predators, and an abundant prey base are required at the release site.