Laysan Duck (Anas laysanensis)

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Image of a Laysan duck
Birds Duck

Introduction

The Laysan Duck (Anas laysanensis), also known as the Laysan Teal, is a small, dark-plumaged dabbling duck endemic to the Hawaiian Islands. Once distributed more widely across the archipelago, it is now restricted to isolated populations in the Northwestern Hawaiian Islands. The species is highly sedentary, largely terrestrial and mostly nocturnal, unusual traits among ducks.

Physical Description

The Laysan Duck is approximately 38–43 cm long and weighs about 420–500 g. Both sexes are mostly chocolate-brown, with contrasting pale-edged body feathers, a prominent white eye-ring and an iridescent purplish-green speculum on the wing.

Plumage varies considerably between individuals. Adults often develop irregular white feathering on the head and neck, a form of leucism that is particularly common in birds older than three years. Juveniles usually have a much less conspicuous eye-ring.

The sexes are similar in overall plumage, but the bill and legs provide useful distinctions. Males generally have a short, spatulate olive-green bill with black blotches on the upper mandible. Females usually have a slightly shorter, paler orange bill with variable black mottling. Both sexes have dull orange legs, although the male’s legs are often brighter. Males are also, on average, slightly larger in several measurements, including bill, tarsus and wing dimensions.

Range and Habitat

The Laysan Duck is endemic to the Hawaiian archipelago. Subfossil evidence indicates that it formerly occurred across much of the Hawaiian Islands, but the species disappeared from the main islands many centuries ago, probably because of human pressure and introduced predators.

For much of the modern period, the remaining wild population was confined to Laysan Island. Wild populations now occur on Laysan Island, Midway Atoll and Kure Atoll following conservation translocations. These islands form part of the Northwestern Hawaiian Islands and lie within the Papahānaumokuākea Marine National Monument.

The species uses a combination of shallow lakes, freshwater seeps, ephemeral wetlands, brackish areas, coastal tide pools and surrounding terrestrial vegetation. Freshwater seeps and temporary wetlands are particularly important for drinking and brood-rearing. Although it can fly, the Laysan Duck is notably sedentary and spends substantial time walking and foraging on land. It generally occurs at low elevation because its range consists of low-lying islands and atolls.

Behaviour and Diet

Laysan Ducks are mostly nocturnal and are often more active on foot than in flight. When startled, they may freeze or run rather than immediately flush. Their short wings and relatively reduced flight musculature reflect adaptation to a largely terrestrial island environment.

The diet is primarily insectivorous but varies with season and local conditions. Recorded foods include flies and their larvae, moth larvae, beetles, ants, cockroaches, brine flies, brine shrimp, amphipods, seeds, leaves and algae. Birds forage both around wetlands and in terrestrial vegetation, switching between food sources when rainfall or water levels alter prey availability.

Breeding is flexible and responds to habitat and food conditions. Nesting on Laysan generally occurs from about April to July, although earlier broods have been recorded. Nests are concealed in native grasses and other vegetation, often some distance from open water. Average clutch size on Laysan is relatively small, about 3.8 eggs, although larger clutches have been recorded at Midway Atoll. Pair bonds may persist between breeding seasons, but pairs can separate during brood rearing and moult.

Identification Tips

Look for a small, dark brown duck with a conspicuous white eye-ring, pale-edged body feathers and a greenish iridescent wing patch. The species often walks through grass or around wetland margins rather than spending long periods swimming.

The combination of a compact body, dark mottled plumage, white eye-ring, short broad bill and terrestrial behaviour is distinctive in its native range. Males tend to show a greener bill with black markings, while females usually have a paler orange bill. Juveniles have a weaker eye-ring, and older birds may show extensive white feathering on the head and neck.

The Laysan Duck should not be confused with the Hawaiian Duck, or Koloa, (Anas wyvilliana). The Hawaiian Duck is generally associated with the main Hawaiian Islands and has different plumage and bill characteristics. Hybridisation with introduced Mallards has also been identified as a conservation concern at potential release sites.

Conservation Status

The Laysan Duck is classified as Critically Endangered on the IUCN Red List and is listed as endangered under the United States Endangered Species Act. Its restricted range, small population, low reproductive rate and dependence on a few low-lying islands leave it vulnerable to severe storms, drought, flooding, tsunamis, disease and other chance events.

Introduced species have caused serious historical damage. Rabbits introduced to Laysan Island consumed much of the island’s vegetation in the early twentieth century, degrading nesting and feeding habitat and bringing the duck close to extinction. The removal of rabbits, protection of Laysan Island and restoration of native vegetation helped the population recover from its historic low point.

To reduce the risk of a single catastrophe affecting the entire species, 42 wild ducks were translocated from Laysan Island to Midway Atoll in 2004 and 2005. The introduced population bred successfully, although it later suffered substantial losses during an outbreak of type C avian botulism. A further conservation translocation established a population at Kure Atoll in 2014.

Current conservation work includes population and reproductive monitoring, freshwater and wetland management, invasive-species control, disease surveillance, habitat restoration and careful management of translocated populations. Climate change is an additional concern because sea-level rise, changing rainfall patterns and more intense storms may reduce the availability of suitable habitat on these low-lying islands.

Frequently Asked Questions

Where does the Laysan Duck live?

The species lives in the Northwestern Hawaiian Islands, with wild populations recorded on Laysan Island, Midway Atoll and Kure Atoll. It uses wetlands, freshwater seeps, shallow lakes, coastal areas and nearby terrestrial vegetation.

Is the Laysan Duck migratory?

No. It is highly sedentary and normally remains near the island or atoll where it lives. Although capable of flight, it does not undertake regular long-distance migration.

What does the Laysan Duck eat?

It mainly eats insects and other invertebrates, including flies, moth larvae, beetles, ants and brine flies. It also takes brine shrimp, amphipods, seeds, leaves and algae when available.

Why is the Laysan Duck endangered?

Its population is small and divided among a few low-lying islands. The species is vulnerable to invasive species, habitat degradation, disease, drought, severe storms, tsunamis, flooding and other catastrophic events.

How did conservationists establish a second population?

In 2004 and 2005, conservationists moved 42 wild Laysan Ducks from Laysan Island to Midway Atoll. The birds reproduced successfully and established a second wild population, although disease later caused significant mortality there.

Is the Laysan Duck active during the day?

It can be seen during daylight, but it is mostly nocturnal. It often forages on land and may walk or remain still when disturbed instead of flying away immediately.

References

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