Circadian habitat use, home range and behaviour of Laysan Teal Anas laysanensis

The Laysan Teal Anas laysanensis is a non-migratory duck that survives as a single relict population on a small remote Pacific atoll, Laysan Island (4 km2). The species suffered range contraction and isolation after mammalian predator introductions to the Hawaiian archipelago. An understanding of spatio-temporal behaviour on Laysan Island may help guide conservation priorities such as habitat restoration and reintroductions on additional islands. This study therefore analysed factors influencing spatio-temporal variation in Laysan Teal’s habitat use. Diurnal, nocturnal and crepuscular (i.e. twilight) behaviour and home range utilisation (95% and 50% fixed kernels) of nesting and non-breeding adults on Laysan Island were determined using radio telemetry. Total home range (mean ± s.e.) was 17.69 ± 4.28 ha with core area use of 2.57 ± 0.54 ha (n = 27). There was little overlap between core diurnal and nocturnal activity centres. Total home range of non-breeders was larger than that of nesters, and crepuscular movements were larger than diurnal and nocturnal movements. Time of day influenced the Laysan Teal’s use of vegetation type and behaviours. Differences in behaviour, prey abundance, and rainfall were observed between years of this study, and Laysan Teal were detected spending more time foraging at night in 2004 during drier environmental conditions compared to 2005, a wet year. Since Laysan Teal do not migrate or disperse from Laysan Island, significant inter-annual differences in rainfall and food abundance are likely to strongly influence resource use and behaviour within their very limited geographic range. These results emphasise that habitat management for threatened species, especially those with restricted mobility and small ranges, should accommodate their circadian use of resources, and inter-annual environmental variability.