The Hawaiian archipelago (covering EBAs 216-218) constitutes the US state of Hawaii and is a chain of volcanic islands which are gradually sinking and moving north-west, away from the 'hotspot' where they originally erupted. The oldest emergent island is Kure Atoll in the North-western Hawaiian or Leeward Islands and the youngest is the island of Hawaii (EBA 218).

Laysan, now a low-lying coral atoll (reaching only 11 m) with no volcanic rock exposed, is part of the North-western Hawaiian group and, at 3.7 km² in size, is the smallest of all EBAs. The native vegetation is mainly scrub and grass, and c.20% of the atoll is taken up by a central saline lagoon.

One of the restricted-range species extinct in this EBA, Acrocephalus familiaris, has a surviving population on Nihoa, but as this island is c.1,000 km south-east of Laysan, and as the two forms (familiaris on Laysan and kingi on Nihoa) are sometimes regarded as separate species, Nihoa is treated as a Secondary Area (s138). Two other islands in the North-western Hawaiian group-Midway, and Pearl and Hermes-have (or had) populations of some of the restricted-range species of Laysan, but these were all introduced.

Only two restricted-range species are extant in the EBA. In 1987 Anas laysanensis was estimated to number c.500 birds, which probably represents the carrying capacity of the habitat; extreme fluctuations in the population have been noted since the 1950s, but these may just reflect different census methods (Marshall 1992). Between 1960 and 1990 Telespyza cantans numbered 5,000-20,000 birds with apparent fluctuations attributable either to unpredictable weather, which has a major influence on breeding success every year, or, again, to variability in census methods (Morin 1992, Morin and Conant 1994). T. cantans also persists on Pearl and Hermes Atoll from an introduction in 1967 (but not on Midway Island, where an introduced population succumbed to predation by rats brought in inadvertently as a result of war activities; as did the introduced population of Porzana palmeri).

Previously undisturbed, Laysan was leased to phosphate miners during the period 1890-1904. The removal of guano (produced by the vast numbers of seabirds) was probably not detrimental to the landbirds, but duck-hunting to provide food and sport for members of the mining community reduced the population of Anas laysanensis. Even greater impact resulted from the introduction of European rabbits Oryctolagus cuniculus in 1903-1904 to provide a source of fresh food independent of supply ships. By 1911 the rabbits had caused massive deterioration of the habitat, and three species of bird, deprived of their natural food supply, became extinct. The subsequent removal of these mammals in 1923 allowed regeneration of the vegetation and the recovery of the two surviving species.

The two endemic species are still classified as threatened today because of their very small ranges and, in the case of Anas laysanensis, very small population, rendering them both forever at risk of extinction from chance events, such as the effects of severe weather or introduced species, particularly the possible accidental introduction of rats from passing ships. The aggressive alien plant, Cenchrus echinatus, could cause detrimental habitat deterioration, but eradication is under way (K. McDermond in litt. 1993).

Laysan is extremely important for seabirds-having some of the greatest nesting colonies in the world, holding 18 species and up to a million breeding pairs (Harrison 1990b)-and is also an important wintering site for Bristle-thighed Curlew Numenius tahitiensis (Vulnerable), a migratory, restricted-range species (see Secondary Area s002), with winter counts of 300-350 individuals during 1988-1991 (Marks and Redmond 1994).

Laysan is protected by the Hawaiian Islands National Wildlife Refuge, which includes the North-western Hawaiian Islands from Pearl and Hermes Atoll to Nihoa, and is uninhabited except when researchers are present.

Recommended citation
BirdLife International (2024) Endemic Bird Area factsheet: Laysan Island. Downloaded from https://datazone.birdlife.org/eba/factsheet/210 on 23/11/2024.