Heavy rainfall triggers increased nocturnal flight in desert populations of the Pacific black duck (Anas superciliosa).

Understanding of avian nocturnal flight comes mainly from northern hemisphere species in seasonal temperate ecosystems where nocturnal flight is often precisely timed and entrained by annual photoperiod. Here we investigate patterns of nocturnal flight in waterbirds of Australian desert ecosystems that fly considerable distances to find temporary water bodies formed from rainfall which is highly unpredictable seasonally and spatially, and when there is sufficient water, they then breed. How they perform these feats of navigation and physiology remain poorly known. Using GPS tracking of 38 satellite tagged Pacific black ducks (Anas superciliosa) in two contrasting ecosystems, before and after heavy rainfall we revealed a key role for facultative nocturnal flight in the movement ecology of this species. After large rainfall events, birds rapidly increased nocturnal flight activity in the arid aseasonal ecosystem, but not in the mesic seasonal one. Nocturnal flights occurred throughout the night in both ecosystems. Long range flights (>50 km in 2 hours) occurred almost exclusively at night; at night the distance flown was higher than during the day, birds visited more locations, and the locations were more widely dispersed. Our work reveals that heavy rainfall triggers increased nocturnal flight activity in desert populations of waterbirds.

Extreme nomadism in desert waterbirds: flights of the banded stilt.

In contrast to well-studied Northern Hemisphere birds with spatially and temporally predictable seasonal migrations, waterbirds in desert biomes face major challenges in exploiting stochastic, rich, yet short-lived resource pulses in vast arid landscapes, leading to the evolution of nomadic behaviour. An extreme example is the banded stilt (Cladorhynchus leucocephalus), an opportunistic colonial breeder at remote inland salt lakes after infrequent rain events. Using satellite telemetry on 21 birds (tracked for a mean of 196.2 days), we reveal extensive, rapid and synchronized movement among individuals to and from salt lakes. Two birds left coastal refugia for the inland following rain, flying 1000-2000 km, while 12 others rapidly moved a mean of 684 km (range 357-1298 km) away from drying inland sites to the coast. Two individuals moved longitudinally across the continent, departing and arriving at the same points, yet travelling very different routes; one bird moving more than 2200 km in less than 2.5 days, the other more than 1500 km in 6 days. Our findings reveal movements nearly twice as long and rapid as recorded in other desert waterbirds. We reveal capability to rapidly detect and exploit ephemeral wetland resource pulses across the stochastic Australian desert.