Justification This species is listed as Critically Endangered because its population exhibits extreme fluctuations within its extremely small range. Conservation action is seeking to remove existing threats or increase the species's resilience to them, and the population is currently increasing. Following the successful reintroduction of birds to Midway Atoll, this species will warrant downlisting after five years if both populations are still self-sustaining, as the species now lies above the population thresholds for listing as Critically Endangered and occurs at multiple locations; but in the meantime it retains this classification as a precautionary measure.

Family/Sub-family Anatidae

Species name author Rothschild, 1892

Taxonomic source(s) AOU checklist (1998 + supplements), Sibley and Monroe (1990, 1993)

Identification 41 cm. Very small, dark duck. Dark head, with some adult males showing slight iridescence, white eye ring, and adults with variable white plumage on head and neck, blotched irregularly. Rest of body chestnut mottled with dark brown. Iridescent speculum appears teal green, or blue. Dark green bill in male, brownish-pale in female. Voice Males have low, soft, hoarse quek, females quack.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

600 - 700

increasing

2 km²

Yes

Range & population Anas laysanensis is endemic to the Hawaiian Islands (USA), where it became confined to Laysan. The birds do not disperse from Laysan today, but sub-fossil remains indicate that it was widespread on the Hawaiian Islands in the past¹², most recently being extirpated from Lisianski Island about 150 years ago. The species was near extinction at the beginning of the 20th century, but the population increased to 500 individuals in 1987³ following the removal of introduced rabbits from Laysan. In 1993, there was a complete breeding failure and severe die-off owing to drought and disease. Poor monitoring at this time impairs accurate population estimates, but post-hoc analysis suggests that the population dropped to 82-127 adults from a peak of 743 birds prior to the drought. Since then, the population has gradually increased⁸; the latest population estimate is 503-682 adult birds on Laysan¹⁸. Apparent population fluctuations over the past century were previously attributed to differing methods and seasons of counts³, but are now thought to relate to genuine changes¹¹. The Laysan population may currently have reached carrying capacity for the island, but 42 individuals were translocated to the two islands of Midway Atoll National Wildlife Refuge in 2004 and 2005; the birds bred successfully in their first year¹ and the founder population increased in size to a total of 104 individuals in 2006¹⁶, reaching c.200 adult and juvenile (post fledging) individuals by the end of 2007^17,20 and predicted to grow to a total of 380 birds²⁰. In August 2008 however the Midway population was hit by a catastrophic outbreak of avian botulism, killing over 160 birds (a decline of up to 40-50%)²¹.

Ecology: The species is non-migratory and characterised by female-only parental care and high adult survival. On Laysan, long-term pair bonds are common, and 3-4 eggs are laid per clutch. On Laysan the timing of breeding varies significantly between years with the beginning of incubation varying from December to July²². It selects different habitats during different times of the day. Most adult birds use dense cover and hide in the terrestrial vegetation during the day. During the evening, and at night¹⁵, it uses the central hyper-saline lake on Laysan, but concentrates near freshwater seeps around the shore⁵, especially when raising young ducklings, which are less tolerant of hypersaline conditions. It nests and rests in dense stands of shrubs and grasses⁶. It feeds principally on invertebrates, but also grass and sedge seeds, and some algae⁸; brine fly Scatella sexnotata is an important prey species whose peak spring abundance is positively correlated with annual brood production of the teal²². Reintroduced birds on Midway Atoll appear to breed successfully at an earlier age and produce larger clutches, probably owing to more food and a low density population. However, duckling survival is low on both atolls.

Threats Random disasters and the limited carrying capacity of the fragile tiny islands are the main threats to its persistence. Historic declines on Laysan leading to the near-extinction of the species are attributed to introduced rabbits and more recently Echinuria uncinata, coupled with drought¹⁹. Since the severe range contraction of the species from the main Hawaiian Islands after the introduction of rats, stochastic events that have already occurred include: the accidental introduction of noxious competitors, extreme weather, and disease epizootics. Additional populations on different islands are needed to reduce the extinction risk to small concentrated populations from alien predator introductions, tsunamis, and hurricanes, as the probability that disasters will affect several islands simultaneously is lower. On Laysan Island, brood rearing habitat is probably an important limiting factor. Freshwater seeps with high invertebrate abundance and adjacent dense vegetative cover are used as duckling nurseries. High incidence of duckling trauma suggests these freshwater seeps may become overcrowded. Reproductive success is sometimes related to brine fly (prey abundance) densities which, in turn, are reduced by drought and low water-levels^6,7,8. During drought conditions, the birds depend more on terrestrial prey¹⁵. Introduced ants (e.g. big-headed ant Pheidole megacephala) are probably competitors for their terrestrial invertebrate prey⁸. Disease or parasitic infestation by the nematode Echinuria uncinata¹⁰ are perhaps one of the greatest potential threats - the catastrophic outbreak of avian botulism killed 40-50% of teal on Midway in 2008²¹. Some alien invasive plants on Laysan have threatened nesting and wetland habitat^4,5, while climate change and associated sea-level rise are further concerns, especially for extremely low-lying islands.

Conservation measures underway CITES Appendix I. Laysan is part of the Hawaiian Islands National Wildlife Refuge. The alien grass Cenchrus echinatus is thought to have been eradicated⁵ and native bunch grass has responded positively⁸. Snow fences were installed 20 years ago to reduce the movement of sand and support natural revegetation⁶. In 2004-2005, 42 wild birds translocated from Laysan Island were released on Midway Atoll and many bred successfully in their first season. Following the success of the releases on Midway, the next translocation is being discussed for Kure or Lisianski islands in the North West Hawaiian Islands to establish a third population, however currently held captive birds are unsuitable for translocation and this would therefore require the establishment of a new captive population from wild stock^17,21. Both islands require some habitat restoration prior to duck translocation; this work is currently underway on Kure¹⁷. During the 2008 avian botulism outbreak on Midway 28 sick birds were successfully treated with anti-toxin, rehabilitated and released, and the rapid removal of sick and dead birds was thought to have prevented the impact of the outbreak becoming even worse²¹.

Conservation measures proposed Continue to monitor the population size and health on both Midway Atoll and Laysan Island. Continue to enhance nesting habitat on Midway by planting native bunch grasses. Enhance brood-rearing habitat on Midway Atoll with small fish-free freshwater wetlands with abundant cover. Use translocation and ecosystem restoration to re-establish four additional populations of Laysan Ducks. On Laysan, continue to stabilise dunes by planting native vegetation⁶. Restore freshwater wetlands on Lisianski and Kure Islands prior to potential re-introduction. Ensure strict procedures to prevent the accidental introduction of exotic plants, invertebrates and animals⁶. Control exotic plants likely to negatively impact the species. Conduct further alien predator eradications to create potential for reintroduction to other larger higher elevation islands. After restored predator-free habitat is available, create a new genetically managed captive population within Hawaii to provide birds for reintroductions to other Hawaiian islands⁸.

References 1. Reynolds and Klaviter (2006). 2. Cooper et al. (1996). 3. Marshall (1992). 4. Morin et al. (1997). 5. M. Morin in litt. (1999). 6. Moulton and Marshall (1996). 7. M. Reynolds (unpublished data). 8. M. Reynolds et al. (2006). 9. R. Shallenberger in litt. (1999). 10. M. Reynolds in litt. (2000). 11. M. Reynolds and G. Ritchotte in litt. (2002). 12. Reynolds and Kozar (2000). 13. US Fish and Wildlife Service (2002d). 14. Anon (2005) 15. Reynolds (2004). 16. Jarrett (2006). 17. USGS (unpublished data, 2007). 18. Reynolds and Citta (2007). 19. Work et al. (2004). 20. Reynolds et al. (2008). 21. M. Reynolds in litt. (2008). 22. Reynolds et al. (2007).

Further web sources of information

Alliance for Zero Extinction (AZE) species/site profile. This species has been identified as an AZE trigger due to its IUCN Red List status and limited range.

Audubon WatchList

U.S. Fish and Wildlife Service - Draft Recovery Plan

Text account compilers Augustus Asamoah, Phil Benstead (BirdLife International), Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International), Isabel Isherwood (BirdLife International), John Pilgrim (BirdLife International), Alison Stattersfield (BirdLife International), Tom Stuart (BirdLife International), Andy Symes (BirdLife International)

Contributors Marie Morin (US Fish & Wildlife Service), Michelle Reynolds (US Geological Survey), George Ritchotte (US Geological Survey), Rob Shallenberger (The Nature Conservancy)

IUCN Red List evaluators Jeremy Bird (BirdLife International), Stuart Butchart (BirdLife International), Andy Symes (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Anas laysanensis. Downloaded from http://www.birdlife.org on 9/2/2010

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

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