A desert waterbird almost sounds like an oxymoron. And it’s true, waterbirds living in arid landscapes face the decidedly difficult task of finding rich, yet short-lived pulses of resources in vast stretches of the desert. Now, researchers studying Australian desert shorebirds reveal that once the birds detect rainfall in the distance, they’re capable of quickly flying a couple thousand kilometers to get to these ephemeral lakes. The findings were published in Biology Letters this month.
Banded stilts (Cladorhynchus leucocephalus) have evolved extreme nomadic behavior. These opportunistic, colonial breeders are famous for their uncanny ability to somehow sense infrequent rainfall and rare flooding events from immense distances away. Then they’ll disappear from their coastal refuges and show up at these remote inland lakes to breed and raise chicks in densely packed colonies. While the coast sustains them during dry times, unlike other waterbird species, banded stilts don’t breed there. “Instead, they move inland and form massive nesting colonies of thousands of pairs when salt lakes flood, feasting on brine shrimp that hatch from eggs which have lain dormant in the dry salt crust for years,” says Reece Pedler of Deakin University.
By attaching tiny solar-powered transmitters, Pedler and colleagues tracked 21 stilts for an average of 196 days. "Banded stilts are exquisitely adapted to the boom-bust cycles of the Australian desert," Pedler explains in a news release. “Our satellite tracking work reveals that they can fly much further and faster than previously thought." Banded stilt flights are nearly twice as long and rapid as reported movements of other desert waterbirds.
Two stilts crossed the continent, from Lake Eyre in the south to the Canning Stock Route in the west. One of them flew more than 2,200 kilometers in less than two-and-a-half days, while the other traveled more than 1,500 kilometers in six. Another two birds left the coast to exploit floods that occurred between 1,000 and 2,000 kilometers inland.
Speed is of the essence: “The Australian brine shrimp that banded stilt feed on have rapid life cycles, and thus the stilts must arrive rapidly after flooding of inland lakes to capitalize on the temporary feast that they provide," Pedler tells New Scientist. “These tiny shrimp grow rapidly and are so numerous that the briny water has been likened to brine-shrimp soup.” After these desert salt lakes dried up, a dozen of the tracked birds traveled between 357 and 1,298 kilometers in order to retreat to coastal refuges, such as Coorong at the mouth of the Murray River.
But how do they know that it rained so, so far away? The cues they use are still a mystery. "One explanation could be that they respond to changes in barometric pressure or distant thunder that could signal rain," Pedler explains. "Or maybe they can smell the recently flooded wetlands on the wind from hundreds of kilometers away."