Coot Birds Can Count, Study Says

James Owen in England
for National Geographic News
April 2, 2003

To most people, coots are noisy, quarrelsome water birds that do a lot of splashing about. But it turns out they are also closet cuckoos. Not only that, they can count.

The discovery was made by Bruce Lyon, a biologist at the University of California, Santa Cruz. His study of an American coot colony in British Columbia, Canada, is the first to show that birds can keep a reckoning of the eggs they lay. It also highlights an extremely rare example of counting by a wild animal.

Supported in part by the National Geographic Society's Committee for Research and Exploration, the research is published this week in the science journal Nature.

While cuckoos are interspecific brood parasites (they lay eggs in nests belonging to other bird species), American coots are conspecific (they target their own species).

There are various reasons why they do this.

Female coots that lose out in the battle for breeding territory will try and offload eggs onto successful nesters. Also, the last few eggs laid in a clutch have a reduced chance of survival. Females that lay them elsewhere should improve their overall breeding success.

In addition, coots have more opportunities for conspecific parasitism than many other birds, according to wildlife biologist John Eadie, from the University of California (Davis) department of wildlife, fish, and conservation biology.

"Coots have large clutch sizes so the number of days during which a host can be found and parasitized [before incubation starts] is greater," said Eadie. "American coots also nest at quite high densities so there are more potential host nests available."

Lyon's four-year study found that conspecific brood parasitism was commonplace among American coots. Over 40 per cent of pairs were targeted, with an average 3.1 eggs left in each nest.

Chick Starvation

This is costly to a host pair because their own young lose out. With starvation already widespread among coot broods—98 percent suffer at least one death—the burden of having extra hungry mouths to feed means even more fatalities. If a parasitic chick survives, one of the host's young is likely to have died.

American coots have responded to this threat by learning to recognize eggs that aren't theirs. Lyon found that 43 percent of host pairs rejected at least one parasitic egg before it hatched.

Continued on Next Page >>


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