Hidden Messages Found in Bird Nest Decorations

The discovery of messages in raptors’ nests has raised the possibility that many bird species encode signals into these structures, with seemingly decorative flourishes actually full of meaning.

Among black kites, scraps of white plastic are used to signal territorial dominance. To other kites, the scraps are a warning sign. To humans, they hint at an unappreciated world of animal communication.

A few species, such black wheatears and bowerbirds, are already known to use nest design in courtship displays. But such communication is considered uncommon and relatively one-dimensional, aimed entirely at finding a mate.

In a study published in Science, researchers describe their careful observations of 127 black kite nests in Spain’s Doñana National Park.

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 plastic displays. Kites with much plastic in their nest were rarely challenged, while those with little were challenged daily, even hourly.

The plastic appears to be a convenient way of codifying and announcing strength, saving kites from indiscriminate or ill-chosen battles. The birds also had access to green and transparent plastics, ostensibly preferring white because of its long-distance visibility.

When the researchers intruded, however, adding extra plastic to nests, challenges paradoxically became more frequent — suggesting that kite community is aware of existing claims, and quick to test would-be cheaters.

Read more in the original article here.