What a black blob tells other birds.

A quirk of flocking birds has allowed scientists to test the idea that a black chest patch works as a badge of status.

In winter, hungry birds often join forces in looking for food, roaming from place to place in flocks. On average, they may find more food than solitary foragers, but a flocking bird that stays too close to a piggy eater can end up hungry. Several studies have documented that birds often avoid flocking with dominant bullies.

This tendency allowed Juan Carlos Senar and Montse Camerino of the Museum of Zoology in Barcelona to see whether siskins use their black chest bibs as an index of dominance. Previous work suggested that the more dominant birds sport the bigger bibs. But do the birds themselves treat the blobs as status symbols?

Yes, the researchers report in the August 22 Proceedings of the Royal Society of London B. They caught wild male siskins and offered them their choice of feeding partners. The birds chose small-bibbed--less dominant--birds twice as often as they chose large-bibbed ones. Enlarging a chest spot with a black marker or slimming it with yellow-green paint changed a bird's desirability as a dining companion. The test birds chose partners without observing aggressive acts, suggesting that they made decisions just by checking the black badge of dominance.