Laysan duck

The Laysan duck (''Anas laysanensis''), also known as the Laysan teal, is a dabbling duck endemic to the Hawaiian Islands. Fossil evidence reveals that Laysan ducks once lived across the entire archipelago, but today survive only on Laysan Island and two atolls. The duck has several physical and behavioral traits linked to the absence of ground-based predators in its habitat. By 1860, the ducks had disappeared from everywhere except Laysan Island. The introduction of European rabbits by guano miners at the end of the 19th century brought the bird to the brink of extinction in 1912, with twelve surviving individuals. Rabbits were eradicated from the island in 1923 and numbers of Laysan ducks began to rise, reaching 500 by the 1950s. In an effort to ensure the long-term future of this duck, 42 birds were translocated to Midway Atoll National Wildlife Refuge in 2002. These thrived in their new surroundings, and another group were later relocated to Kure Atoll.

Taxonomy

Named by Lionel Walter Rothschild in 1892, the Laysan duck is named after Laysan island, one of the Northwestern Hawaiian Islands. It is a member of the mallard clade of dabbling ducks, and is a highly unusual species, both behaviorally and genetically. Recent evidence suggests they originated from an east Asian, southern hemisphere ancestor of mallards, not from stray migratory mallards (''Anas platyrhynchos'') as had been reported in the past.

Description

The Laysan duck is teal-sized and dark brown, with a prominent white eye-ring. The bill is short and spatulate, dark green with variable black blotching in males, and dull orange with variable black blotching in females. The Laysan duck usually has a ring of fat around its neck. Some males show faint iridescence on the head or neck and have slightly upturned central tail feathers. The wing has an iridescent purplish-green patch (speculum feathers) in both sexes. Leucistism, or extensive white feathering, is common on the head and neck of older birds. The legs and feet are orange, usually brighter in the male. The annual pre-basic molt is complete, and the ducks lose all their flight feathers and become incapable of flight until new feathers grow in. Wild ducks have been known to live to the age of twelve years, and captive birds have lived to the age of eighteen.

Behavior

The Laysan duck is a poor flyer, but walks and runs well, with a pelvic girdle adapted to terrestrial foraging. Its wings and wing muscles are reduced; it prefers to freeze in place when pursued. Energetic foraging behavior includes a fly-snapping sprint through '' Neoscatella sexnotata'' brine fly swarms. With necks outstretched, and bills close to the ground, the ducks run along a mudflat and as clouds of flies rise up in front, snap them up by rapidly opening and closing their bills. The ducks also will dabble and filter feed along lake shallows, shore, and in upland vegetation for macroinvertebrates, algae, leaves, and seeds. During the day, and especially in the breeding season, they prefer to hide among the grass and shrub vegetation, helping them to avoid avian predators such as frigatebirds. They prefer to venture out in the open and feed on the lake from dusk til dawn, although there seems to be marked variation from year to year according to the availability of food items.

Reproduction

Pair formation begins in autumn, and nest building begins in spring. The female builds a well-concealed nest on the ground below dense vegetation, especially ''Eragrostis variabilis'' bunchgrass. The nest is a shallow bowl lined with dead grass and down feathers. Egg-laying typically occurs from April to August. Average clutch size on Laysan Island is approximately four bird egg/eggs. The newly established population on Midway lays larger clutches, presumably because of better availability of food. Ducklings are precocious and feed on their own day two after hatching, but are guarded, brooded, and led to foraging sites by the hen for approximately 40 to 60 days.

Status and conservation

Decline to near-extinction

The decline of the Laysan duck began between AD 400 and 1000, with the colonization of the Hawaiian Islands by Polynesians and associated non-native mammalian predators. By 1860, the ducks disappeared from all but Laysan Island (the duck's namesake), most likely due to predation by introduced rats. Like many isolated island species, the Laysan duck evolved in an environment lacking mammalian predators, and is ill-suited to defend itself against non-native ground hunters, such as humans, rats, pigs, and small Asian mongooses. For example, Laysan ducks are more likely to freeze their movement rather than flush or fly when startled— a strategy well suited for cryptic defense against Hawaii's native flying predators, but ineffective against ground predators. The Laysan duck can still fly, but not very well and not for long distances; it does not disperse between islands.

The Laysan duck found refuge through most of the nineteenth century on rat-free Laysan Island, surviving within the smallest geographic range of any duck species worldwide (). Laysan Island gained federal protection in 1909, with the establishment of the Hawaiian Islands National Wildlife Refuge. However, devastation of the island's vegetation by introduced domestic rabbits brought the duck to the brink of extinction in 1912, with an all-time low population of seven adults and five juveniles.

It is also said by the Fish and Wildlife when they returned to eliminate the last of the rabbits that there was just one Laysan duck hen that still existed on the Island on a nest with broken eggs in it. By this information would pertain that all Laysan Teals are from this female and the fact they can be fertile up to 1 month after copulation.

Recovery

After many domestic rabbits starved and the remaining ones were eradicated by biologists in 1923, the ducks began to recover, increasing to a population of about 500 individuals by the 1950s. Congress passed the Endangered Species Preservation Act in 1966, and in 1967 the Laysan duck was declared an endangered species with federal protection. However, population bottlenecks occurred, such as the severe 1993 El Niño drought and food shortage, which reduced the number of ducks to about 100. Today, breeding and survival of the birds are closely tracked. Since 1998, a sample of birds have been fitted with unique leg bands or radio transmitters for monitoring reproductive success and survival, revealing that typically only 30% of ducklings on Laysan Island survive to fledge. In 2004, the population grew to an estimated 576 ducks.

In October 2004 and 2005, 42 Laysan ducks were translocated to Midway Atoll National Wildlife Refuge as a collaborative effort between the United States Geological Survey and Fish and Wildlife Service to establish a second population of ducks in the wild. The creation of a second population, since disaster is unlikely to strike both atolls simultaneously, reduces the risk of extinction by random catastrophes such as drought, hurricanes, tsunamis, disease outbreaks (like avian influenza

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