Want to impress your neighbors?

If you can't afford a gardener or swimming pool, you might consider a strategy that has worked for the Black Kite -- decorating your home with bits of white plastic trash.

Pairs of Kites in Donana National Park routinely scavenge white plastic scraps for their nests, and observations show the fanciest nests -- almost completely filled with plastic -- are owned by the healthiest and most productive pairs that control the largest range.

Why would a bird work so hard to clean up the neighborhood? Are plastic nests are warmer or more comfortable?

Apparently not, since the Kites rejected superior materials offered by researchers. Also, only white plastic was accepted -- the birds refused all other colors. Are they fishing for a mate, like Bowerbirds? That seems unlikely, since males and females both contribute the nest.

So -- whom are they trying to impress?

Maybe they want to impress their enemies. Birds with the most festooned nests were also the best at driving away "floaters" -- kites who try to steal from other's territories. By creating a highly visible signal, the birds are making a veiled threat that is instantly recognized by poachers -- an advertisement that they are strong enough to defend their stake. Even more amazing, this universal signal is clearly an innovation, since white plastic has only been available for a few decades.

But not all birds are ready to take on the responsibility of a status symbol. More than a third of the mated pairs -- the very young and very old -- refused to decorate their nests even when the perfect materials were offered to them. In fact, low-ranking pairs actually removed extra plastic added by researchers -- and for good reason. "Overdecorated" nests were more likely to be successfully targeted by outsiders. Just as in humans, the very young and very old couples preferred to economize, avoiding an inappropriate show of wealth.

So the next time you consider a home improvement ask yourself -- what is your true motivation? To impress your friends -- or earn the respect of your adversaries?

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