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Science Notes: Nomadic birds chase the rain in Australia; Thorns and predators help plants survive

Nomadic birds chase the rain in Australia

The banded stilt, a graceful, nomadic water bird found in inland salt lakes in Australia, can somehow sense and move toward rainfall hundreds of miles away.

Australians often spot the birds within days of rainfall, said Reece Pedler, a biologist at Deakin University in Australia. And then, abruptly, the birds will disappear.

The mystery, he said, is: “How do these birds know when to leave one place for another, and how do they do it so fast?”

To better understand the movements of the nomadic birds, Pedler and his colleagues tagged 21 banded stilts with satellite transmitters. Their findings appear in the journal Biology Letters.

One tagged bird flew to a saline wetland more than 1,000 miles away in less than 2½ days. Another bird took six days but ended up in the same area. Other tagged birds made overnight flights of about 200 to 400 miles.

The banded stilts are interesting because their movements are so sudden and unpredictable. While many other birds migrate, Pedler said, most do it seasonally, “on a predictable time scale, and have time to plan, prepare and adjust flight-muscle mass.” Exactly how the banded stilts know when and where to travel is still a mystery, he said, but the satellite trackers provide important details about their gypsylike movements.

Thorns, predators help plants survive

Carnivores eat herbivores, and herbivores eat plants. So how do plants manage to thrive? Either by growing prickly thorns or by putting down roots in areas where carnivores are more likely to roam, researchers report in the current issue of the journal Science.

The scientists studied acacia trees in Kenya and the antelopes called impalas that eat them, along with the predators that eat the antelopes.

The impalas feast on two species of acacia trees in the savanna. One is full of thorns; the other is not.

Impalas generally prefer to eat the less thorny plants, said an author of the study, Adam T. Ford, an ecologist at the University of British Columbia.

When Ford removed thorns from the thorny variety and attached them to branches from the less thorny variety, the antelopes changed their preference.

“It’s the thorns that ultimately dictate what the impala want to eat,” he said.

The researchers also attached GPS collars to impalas and two of their predators, leopards and African wild dogs. They found that the predators tended to lurk in bushier areas, where the nonthorny acacias thrive. So for the impalas, there is a trade-off. They can venture into a dangerous area full of their preferred food or they can spend time in safe areas and eat the acacias they don’t like as well.

“And from the plant’s perspective,” Ford said, “it appears that growing thorns is as efficient a way to protect yourself as having predators around.”

– New York Times