January 21, 2011

Trashy Nest Shows Bird’s Ferocity

You've heard the saying: One man's trash is another man's treasure - and when it comes some birds, our trash can be the perfect choice of material for their nests, according to Spanish research released Thursday.

By examining 127 nests of black kites in Spain's Donana National park, researchers reported in the journal Science that the strongest birds showed their ferocity by decorating their homes with lots of white pieces of plastic they find littering the ground.

And only white would do, said scientist Julio Blas of the Spanish National Research Council.

"The amount of decoration is related to the fighting ability of the individuals," Blas told the AFP news agency.

Birds of a certain age -- those between seven and 12 years old -- tended to use the most decorations. "They prefer plastic, and they specifically prefer white plastic which makes the nest more visible not only to humans but to other kites," he said.

The extra ornamentation, which usually accumulated about 20 days before the female laid her eggs, seemed to invite more clashes with other aggressive, highly territorial birds.

But those who had the most white plastic in their nests were "also found to be the most capable of defending their territory from intruding black kites," the study said.

The researchers, performing an experiment, attached white plastic to the nests of both younger and older birds. They found that black kites who were not in top fighting shape quickly removed the plastic pieces.

"This could be similar to the use of different colors for the belts of judo or karate fighters," said Blas. "You don't want to have a color that doesn't match with your fighting capability because you won't get any benefit from it."

Ornithologists have also marveled over the ability of other birds that add sticks, shells and even berries to their nests and other structures to impress mates.

Among black wheatears, a small songbird found in North Africa and Spain, males show off their strength by the size and number of stones they use in their nests. And well-decorated stick structures called bowers signal that a male bowerbird is able to keep other males from stealing its decorations.

But while these birds decorate their nests to attract mates, the male black kites do it merely to show their strength, Fabrizio Sergio, an ecologist at Donana Biological Station in Spain, told the French news agency.

Sergio said nest decorations were correlated with how fit the birds were. And potential intruders took notice. Birds interested in stealing food or commandeering a nest almost never bothered the most decorated nests, but plain nests could be raided up to six times per hour.

Timothy Wright, a behavioral ecologist at New Mexico State University in Las Cruces, thinks this may be the first study to show that organisms use nest decorations for more than just courtship.

"It's a very thorough demonstration that such signals may function in the context of territory defense," he said. "I think few ornithologists will look at nests in quite the same way again."


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