Justification of Red List Category
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 was increasing following the successful reintroduction of birds to Midway Atoll, however outbreaks of avian botulism and a tsunami in 2011 appear to have caused major setbacks to the recovery. The species is consequently precautionarily maintained as Critically Endangered, since although it now occurs at two locations and was recently translocated to a third island, population fluctuations have continued within the past five years.
The total population on Laysan Island was estimated at 521 birds (95% CI: 492-549) in 2010, with probably over 400 individuals (between 268 and 473) on Midway in 2010 (M. Reynolds in litt. 2011). Twenty-eight individuals were translocated to Kure Atoll in 2014. This suggests that the population numbers c.500-680 mature individuals in total.
The population on Laysan Island has increased gradually since a low during the early 20th century, owing to the eradication of invasive alien taxa; however, it has fluctuated between 100 and ~700 birds in the last two decades. Population estimates for the species on Laysan Island indicate that it had been increasing between 1994 and 2010, although apparently the trend has not been consistent (Seavy et al. 2009, M. Reynolds in litt. 2011); however, the species appears to have suffered a c.50% decline in its adult population on Laysan following the winter storms and tsunami of early 2011 (J. R. Walters in litt. 2013). A second population established on Midway Atoll in 2004/2005 quadrupled in three years (Reynolds et al. 2007), but suffered a setback when over 160 birds were killed in an outbreak of avian botulism in August 2008 (M. Reynolds in litt. 2008). An outbreak of this disease has occurred every year since (M. Reynolds in litt. 2011, 2012, J. R. Walters in litt. 2011). Despite this, the overall population is estimated to have increased at a rate of under 20% over the last ten years.
The species is endemic to the Hawaiian Islands (U.S.A.), where it became confined to Laysan Island. The birds do not disperse from Laysan today, but sub-fossil remains indicate that it was widespread on the Hawaiian Islands in the past (Reynolds and Kozar 2000), 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 1987 (Marshall 1992), 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 gradually increased, reaching an estimated 521 birds in 2010 (M. Reynolds in litt. 2011).
Apparent population fluctuations over the past century were previously attributed to differing methods and seasons of counts (Marshall 1992), but are now thought to relate to genuine changes (M. Reynolds and G. Ritchotte in litt. 2002). With the Laysan population possibly approaching carrying capacity, 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 year (Reynolds and Klaviter 2006). The founder population increased in size to a total of 104 individuals in 2006 (Jarrett 2006), reaching c.200 adult and juvenile (post-fledging) individuals by the end of 2007 (USGS unpublished data, Reynolds et al. 2008) and predicted to grow to a total of 380 birds (Reynolds et al. 2008). Although being hit by an outbreak of avian botulism in 2008 which killed over 160 birds (a decline of up to 40-50%) (M. Reynolds in litt. 2008), the preliminary estimates from Midway placed the population in 2010 at c. 350 (M. Reynolds in litt. 2010).
The Laysan population is believed to have been reduced by 50% following a tsunami in March 2011 (J. R. Walters in litt. 2013). On Midway, approximately 20-30% of the banded adult birds observed before this tsunami were not observed afterwards (M. Reynolds in litt. 2012). In 2014, 28 individuals were translocated from Midway Atoll to Kure Atoll, a mammalian predator-free island which lies approximately 1,350 miles north-west of Honolulu (Ward and Fredrickson 2014). As of early May 2015, 19 ducklings had hatched on the island (Anon. 2015).
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. The timing of breeding varies significantly between years, with the beginning of incubation varying from December to July (Reynolds et al. 2007). 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 night (Reynolds 2004), the species uses the central hyper-saline lake on Laysan, but concentrates near freshwater seeps around the shore (M. Morin in litt. 1999), especially when raising young ducklings which are less tolerant of hyper-saline conditions. It nests and rests in dense stands of shrubs and grasses (Moulton and Marshall 1996). It feeds principally on invertebrates, but also grass and sedge seeds, and some algae (Reynolds et al. 2006a); brine fly Scatella sexnotata is an important prey species whose peak spring abundance is positively correlated with annual brood production of the teal (Reynolds et al. 2007). Reintroduced birds on Midway Atoll appear to breed successfully at an earlier age and produce larger clutches than birds on Laysan, probably owing to more food and a low population density. On Midway, individuals in their first year and produce an average clutch of seven eggs, whereas birds on Laysan nest in their second year, producing an average of 3.3 eggs (Walters and Reynolds 2013). Duckling survival is low on both sites.
Random disasters and the limited carrying capacity of the fragile tiny islands are the main threats to the species's persistence. Historic declines on Laysan leading to the near-extinction of the species are attributed to introduced rabbits and, more recently, the parasitic nematode Echinuria uncinata, coupled with drought (Work et al. 2004). 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.
In March 2011, an earthquake off the east coast of Japan triggered a tsunami that arrived at the north-western Hawaiian Islands at night and partially inundated Midway Atoll and Laysan Island (M. Reynolds in litt. 2012). It is reported to have over-washed 60-78% of Eastern Island and 15-20% of Sand Island, and affected c.15% of the species's breeding habitat on Laysan (U.S. Fish and Wildlife Service 2011, M. Reynolds in litt. 2012). A botulism outbreak followed due to the more than 110,000 dead albatross chicks left by the flooding (U.S. Fish and Wildlife Service 2011, M. Reynolds in litt. 2012). Freshwater wetlands were also contaminated with sea water and carcasses (M. Reynolds in litt. 2012). Most of the vegetation on Eastern Island was lost. Prior to the tsunami, two winter storms struck in January and February, bringing high wind and extensive flooding. Following the winter storms and tsunami, the population experienced complete reproductive failure (M. Reynolds in litt. 2012).
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 (Moulton and Marshall 1996, M. Reynolds unpublished data). During drought conditions, the birds depend more on terrestrial prey (Reynolds 2004). Introduced ants (e.g. big-headed ant Pheidole megacephala) are probably competitors for their terrestrial invertebrate prey (Reynolds et al. 2006b). Disease or parasitic infestation by the nematode Echinuria uncinata (M. Reynolds in litt. 2000) are perhaps one of the greatest potential threats - the catastrophic outbreak of avian botulism killed 40-50% of teal on Midway in 2008 (M. Reynolds in litt. 2008, Work et al. 2010), and an outbreak of this disease has occurred every year since (M. Reynolds in litt. 2011, 2012, J. Walters in litt. 2011). Some alien invasive plants on Laysan have threatened nesting and wetland habitat (Morin et al. 1997, M. Morin in litt. 1999), including the central hyper-saline lake where the species forages (VanderWerf 2012). The wetlands on Midway are threatened by future flooding events and require periodic maintenance, including management of wetland plants and algae and the removal of alien mosquito fish (Gambusia affinis) (VanderWerf 2012).
Having a distribution on relatively low-lying islands, this species is potentially susceptible to climate change through sea-level rise and shifts in suitable climatic conditions (BirdLife International unpublished data). Other threats faced by the species include accelerated filling of the interior lake and freshwater seeps due to alien wetland plant species, and erosion of dunes from storm impacts (M. Reynolds in litt. 2011).
Conservation Actions Underway
CITES Appendix I. Laysan is part of the Hawaiian Islands National Wildlife Refuge. The alien grass Cenchrus echinatus is thought to have been eradicated (M. Morin in litt. 1999) and native bunch grass has responded positively (Reynolds et al. 2006b). Snow fences were installed 20 years ago to reduce the movement of sand and support natural revegetation (Moulton and Marshall 1996). A comprehensive restoration plan for Laysan Island has been developed, some sections of which are underway (U.S. Fish and Wildlife Service 2009). In 2004-2005, 42 wild birds translocated from Laysan Island were released on Midway Atoll and many bred successfully in their first season. Management on Midway Atoll includes monitoring the ecology and demography of the species as well as the enhancement and creation of freshwater wetland habitats (VanderWerf 2012). Following the success of the releases on Midway, the next translocations were discussed for Kure or Lisianski Islands in the north-west Hawaiian Islands (USGS unpublished data, M. Reynolds in litt. 2008) and in 2014, Kure Atoll received 28 individuals from Midway Atoll (Ward and Fredrickson 2014). 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 worse (M. Reynolds in litt. 2008). Management strategies have been initiated on Midway Atoll that should reduce the future impact of avian botulism outbreaks, including: annual flooding of the concrete-lined catchment during the summer months; drainage and cleaning of the catchment in the autumn or winter months to remove accumulated debris and seabird remains; vegetation removal around wetlands to allow carcass detection; weekly population monitoring that includes carcass removal and searches for sick birds; wetland carcass searches daily during the summer months; and use of heavy equipment and portable pumps each year to improve water quality (Work et al. 2010).
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.
Text account compilers
Symes, A., Taylor, J., Westrip, J., Bird, J., Ashpole, J, Benstead, P., Butchart, S., Calvert, R., Isherwood, I., Pilgrim, J., Stattersfield, A., Stuart, T.
Shallenberger, R., Morin, M., Walters, J., Reynolds, M., Ritchotte, G.
BirdLife International (2022) Species factsheet: Anas laysanensis. Downloaded from http://www.birdlife.org on 25/01/2022. Recommended citation for factsheets for more than one species: BirdLife International (2022) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/01/2022.