The chicken was eaten before the egg

For instance, predators that have evolved a taste for a certain prey might also develop a taste for the prey's eggs, said Alan de Queiroz and Javier Rodriguez-Robles.

"Feeding on the eggs of birds or of squamate reptiles (lizards and snakes) tends to occur in lineages that already feed on birds or squamates," explain the authors.

It might just be that the prey and its eggs are in the same location, but there is another possibility. Snakes use chemical cues to recognize prey, and the authors suggest the snakes may recognize eggs as potential food because of the chemical similarities between eggs and the corresponding animals.

"The effects of predispositions on the origins of egg-eating and, ultimately, the evolution of highly specialized egg-eating taxa, represent subtle but important historical influences on the present-day attributes of species," the authors concluded.

The study will appear in the May issue of the American Naturalist.

Copyright 2006 by United Press International