coots count their eggs before they’re hatched

The coot, a common water bird, can recognize and “count” its own eggs, according to a study published in the April 3 Nature by biologist Bruce E. Lyon of the University of California at Santa Cruz. Coots often lay their eggs in another coot’s nest, hoping the stranger will take up the heavy burden of raising and feeding its young. If the host bird thinks the foreign eggs are her own, she’ll reduce her clutch size by the number of foreign eggs. Until now, many researchers had speculated the host adjusted the number of eggs she lays based on sense of touch — when the female feels like she’s sitting on the right number of eggs, the development of new eggs stops. But after studying hundreds of coot nests in British Columbia, Lyon has found that coots use an elementary form of counting to help them keep track of their eggs. The eggs can vary by color and speckle pattern, and the more dissimilar in appearance the foreign eggs are to the host’s eggs, the more likely the mother is to shunt the foreign eggs aside — to a likely death — and lay her normal number of eggs. Since the birds are using visual clues to decide how many eggs to lay, Lyon claims this is an example of counting. “These birds are looking at their nests and counting only those eggs they recognize as their own to make a clutch-size decision,” he said in a press release. “That’s pretty amazing for a ‘stupid’ bird like a coot,” Lyon added. “It’s very satisfying to rescue a study animal from a bad rap.”

This news brief appeared in the Random Data column of the Boston Globe’s Health/Science section on 4/08/2003.