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Speedy birds track down remote desert rain

Nomadic birds Satellite tracking of Australian banded stilts reveals they fly massive distances at fast speeds after 'sniffing out' inland desert lakes, making them one of the fastest of the nomadic water birds.

The birds travel vast distances to capitalise on the short-lived food supplies and breeding opportunities provided by inland salt lakes, says Reece Pedler of Deakin University, who is studying the bird's movements as part of his PhD.

"They are nomadic species that go where the going's good," says Pedler.

It's been known for some time that the banded stilt disappears from the coast when there are big rainfall events in the inland. These rare rain events encourage large numbers of brine shrimp to hatch, producing a super nutritious "shrimp soup" available for a brief period of time.

But the exact movements of the birds have been shrouded in mystery.

Pedler used the latest in light-weight solar-powered satellite trackers to get a detailed look at the movements of 21 banded stilts over two years.

He tagged birds in Lake Eyre, which was in the process of drying out, and others in the Coorong at the mouth of the Murray River. The Coorong acts as a coastal refuge for the birds in the dry season.

The findings by Pedler and colleagues are published today in the Royal Society journal Biology Letters.

They confirmed the stilts were moving between different sites depending on the rain but a key finding was the distance and speed they flew.

"They are capable of covering massive distances in really short periods of time," says Pedler, adding that the banded stilt flies further and faster than other nomadic water birds such as flamingoes and ducks.

"The other really interesting finding is that the birds appear to be responding to common cues coming from sites that are hundreds or thousands of kilometres away," says Pedler.

Satellite tracking showed that two separate birds flew from the drying Lake Eyre to a flooded desert salt lake in Western Australia but each took different routes.

One bird flew in a flock that travelled about 2200 kilometres in 2.5 days. It went up through Central Australia visiting other salt lakes en route to Western Australia.

The other bird flew a 1500-1600 kilometre route taking 6 days and travelling through the western parts of South Australia and the lower goldfields of Western Australia.

"It seems like these birds are probably responding to the same distant cues but travelling independently," says Pedler.

He says the birds are moving in a very different way to waders that migrate from Australia to the Northern Hemisphere in response to predictable annual cycles reflected in the length of the day.

"Banded stilts are moving according to the conditions and not on predictable cycles," he says.

"They are moving when there is rainfall and pulses of productivity on these desert lakes and the places that these pulses of productivity are going to occur are not known. The birds have to be ready to fly long distances and breed at short notice."

Barometric pressure

Banded stilts may be detecting the rain's invigoration of desert lakes by sensing changes in barometric pressure, says Pedler.

Alternatively, they could be smelling the salt lakes on the breeze or hearing distant thunder.

Some birds moved rapidly after rain while others only moved a few weeks after the lakes had been flooded.

"The question is whether they sensed some rainfall many weeks earlier and then remember it, and planned to move there. Or were they sensing some other cues?" says Pedler.