Laysan duck

The Laysan duck (Anas laysanensis) is also known as the Laysan teal due to its small size, although its habits are not teal-like in all respects. It has a claim to be the world’s rarest duck, being found in the wild only on the small uninhabited island of Laysan in the Hawaiian chain some 930 miles northwest of Honolulu, and on two other small islands that form part of Midway Atoll. Laysan island is about a mile and a half long and one mile wide.

It has “critically endangered” status on the IUCN Red List of endangered species. Efforts are therefore being made to preserve its natural environment and to breed captive populations in locations in other parts of the world. It can, for example, be seen the Slimbridge Wetland Centre in Gloucestershire, England.

Appearance

The Laysan duck is around 41 centimetres (16 inches) in length. The body is largely brown, having a mottled appearance between light and dark shades. There is a green or blue speculum patch on the wings (upper secondaries). The head is dark brown, with some males having a greenish sheen to the back of the head. A white ring around the eye is a prominent feature, the size of the ring varying between individuals. The bill is dark green in males and light brown in females. The legs are orange.

Habitat

The islands of Laysan and Midway Atoll are notable for having very little fresh water. Laysan has a large central lake that is extremely saline (three times more so than the ocean), and fresh water is only found seeping through the vegetation close to the shore. The saline lake is, however, where the ducks’ main food source, the brine fly, is found, so the ducks need to move between these habitats at different times.

The Laysan duck is most active at night, spending the day hidden in dense vegetation across the island. During the breeding season the ducks tend to spend less time on the lake, due to the ducklings having little tolerance of highly saline conditions.

Behaviour and Feeding

The Laysan duck is less likely to fly than to walk or run. However, it is a strong, fast flyer with rapid wing beats. When feeding on brine flies it will run across the mud with neck stretched out, hoovering up the swarm in its open bill as it goes.

They also feed on shrimps, moths, insect larvae and algae, plus grass and sedge seeds.

Female Laysan ducks quack, whereas males make a softer and hoarser noise.

Breeding

The breeding season is generally from autumn to spring, but the timing of incubation can vary considerably depending on conditions, anything from December to July being possible.

Pair bonds are often long-term. The female Laysan duck builds the nest, consisting of a shallow depression lined with dead grass and down, well hidden in the vegetation. The clutch is usually three or four eggs, although it has been noted that clutches on the Midway islands tend to be larger.

The ducklings can feed themselves from only a few days old, but are guarded by their mother for up to 60 days after hatching, with family groups being shepherded around in search of food.

Conservation

There is always a survival problem for a species that occupies a limited or specialised ecological niche, should that ecology come under threat. That was certainly the case with Laysan when the island was occupied in the late 19^th and early 20^th century by a small number of people who made disastrous changes to its ecosystem by, for example, introducing rabbits and other non-native species. Three endemic bird species were driven to extinction (the Laysan millerbird, Laysan rail and Laysan ‘apapane) and the Laysan duck was lucky to survive.

As it was, numbers of ducks declined to an alarming extent, and the population has fluctuated markedly over the past hundred years, possibly dipping below 100 birds at various times. Given the existence of “natural” threats such as drought and disease, a population at such a level is not far above extinction.

One conservation move has been to extend the range of the Laysan duck to other uninhabited islands or protected environments, the idea being that, should one population be wiped out, others would survive. The population mentioned above, on two of the Midway islands, was introduced there in 2004 and 2005, and seems to be doing well. Plans are now being made to introduce Laysan ducks to a third Hawaiian island, namely Kure Atoll. Another possible site for a translocation is Lisianski island, Laysan’s nearest neighbour.

Preserving and restoring the ecosystem on Laysan itself is also of vital importance. This has included work to prevent sand dunes from spreading, the removal of alien grass species, and the planting of native bunch grass.

The current population on Laysan, at about 700 birds, is possibly about as high as is sustainable. The freshwater seeps, mentioned above, become very crowded during the breeding season, leading to high duckling mortality. However, the Midway population, at about 350, seems to be susceptible to growth.

The Laysan duck’s “critically endangered” status may therefore not be as alarming as might at first be thought. It is a “back from the brink” species, the numbers of which are always likely to be low due to the small number of suitable habitats. However, its numbers in the wild are no longer declining, and there are back-up populations elsewhere, at places like Slimbridge, should disaster befall the islands where it lives.

© John Welford