Brood parasitism among females of the same species is common in certain fishes, insects, and birds, including coots. Host parents bear a high reproductive cost when raising chicks that are not their own, but the mechanisms employed by these animals to overcome brood parasitism have been unclear. In the April 3 Nature, Bruce E. Lyon from the University of California, Santa Cruz, US, shows that egg recognition and counting are used by coots to reduce costs of conspecific brood parasitism (Nature, 422:495-499, April 3, 2003).

Lyon compared American coot pairs that accepted parasitic eggs ('acceptors') with pairs that rejected them ('rejectors'). He observed that acceptor females produced a lower final number of their own eggs. Rejector females, however, did not reduce their own final clutch size. Recognition without rejection also occurred and some hosts banished parasitic eggs to inferior outer incubation positions.

"Females combine egg recognition...

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