London: A new Spanish study has suggested that black kites decorate its nest with large amounts of rubbish to prevent trespassing.
It is a symbol of success, apparently-the biggest collections of plastic are displayed by the black kites with the most chicks and the best territory.
The Spanish research team said the strips, mostly from old bags, are a signal to other birds that the incumbent will put up a fierce fight if any rival tries to move in on the local patch.
"People who``ve worked with black kites and even red kites, their cousins, had noted these birds`` nests were often littered with rubbish, but this is the first time the function of this decoration has been studied," the BBC quoted Fabrizio Sergio, as saying.
"It is not only white plastic-they surely prefer that-but they can actually use a wide range of materials, including cloth and paper," he said.
Sergio and colleagues from the Donana Biological Station wanted to establish if this activity represented a form of communication and, if so, what it was saying.
Over a period of five years, they observed the behaviour of the kites and the nature of their nest decoration. They even intervened on occasions to change the adornment to see how the birds would react.
The team found that the strongest birds in a middle age bracket were the ones with the most plastic. The very young and the very old had hardly any at all.
"The white plastic clearly functions as a threat to other individuals of the same species - to other kites. It``s basically a ``keep away, no trespassing`` signal. A comparison with humans would be the notices placed on the gates of certain nice houses which say ``beware, guard dog,``" he said.
The findings were reported in Science magazine.