Ornithologists at Consejo Superior de Investigaciones Científicas in Seville, Spain, have discovered that the black kite, a medium-size bird of prey, likes plastic. The strongest and most viable black kite couples collect white pieces of plastic to decorate their nests. The eye-catching ornaments show other birds that they command a large territory and are strong enough to protect it.

The ornithologists observed 127 kite nests in Doñana National Park in Spain and found that 77 percent of them were decorated. The male and female started the collection 20 days before egglaying began. The ornamented nests primarily belonged to the strongest and most dominant birds ages 7 to 12 years old. Almost no ornamented nests appeared among very young or very old birds (up to 25 years). In an experiment in which the ornithologists placed plastic in the nests, most young and old birds got rid of the plastic pieces, while birds in the middle age group kept it.

The ornithologists concluded that the presence of white plastic in the nest indicates strength; if a nest is empty, its owner is vulnerable to other, stronger kites.