Raptors don't lie. At least, not with plastic. Black kites are a raptor variety that lives on multiple continents, and like several other varieties of bird (including the crafty bowerbirds), they're avid decorators. For whatever reason, these black kites are terribly fond of white plastic, and the birds use these bits of our refuse to decorate their nests. Scientists who studied these birds in Spain report in Science this week that there is a meaning—and a strict honesty—to the decoration scheme.
They found that, several weeks before females laid eggs, birds festooned their nests with pieces of white plastic. Fitter birds, in possession of the best territory, tended to use more plastic. Weaker birds, with less-desirable territory, used less. Elderly and very young birds used none. Territorial confrontations are common among kites, and proved closely linked to displays of plastic. Kites with much plastic in their nest were rarely challenged, while those with little were challenged daily, even hourly. [Wired]
With so much at stake, you might think these raptors have the ideal motivation to cheat—decorating more liberally than their status would allow, perhaps, as a "don't mess with me" message to their rivals. But not so, Fabrizio Sergio and his team found. Kites tell the truth with their status symbols because it's not worth the risk of being caught in a lie.
To test its ideas, the team made additions to the nests of kites that had hardly any plastic. Almost immediately the owners of those nests started stripping out the plastic. The birds knew that to make an extravagant display would invite challenges, said Dr Sergio, and very young or elderly birds would not risk picking fights they could not win. "Cheating is punished," he added. [BBC News]
Sergio's team studied 127 birds
over the course of five years. But naturalists have noticed kites decorating their nests in such a fashion since the 1800s—long before we humans were using and discarding plastic bags left and right. Sergio says that while black kites prefer pieces of white plastic, they would also use other colors of plastic and paper in smaller amounts. Before humans began throwing out plastic, he says, maybe the birds adorned their abodes in paper or cloth.
“And before that, though we can only of course guess, maybe brightly colored feathers of other birds and the white wool of sheep or deer,” he said. “Or perhaps the behavior evolved after these materials became available.” [The New York Times]
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Image: F. Sergio
