The evolution of egg rejection by cuckoohosts in Australia and Europe

Cuckoo (Cuculus canorus) Science Article 3


Exploitation of hosts by brood parasitic cuckoos is expected to stimulate a coevolutionary arms race of adaptations andcounteradaptations. However, some hosts have not evolved defenses against parasitism. One hypothesis to explain a lack of hostdefenses is that the life-history strategies of some hosts reduce the cost of parasitism to the extent that accepting parasitic eggs in thenest is evolutionarily stable. Under this hypothesis, it pays hosts to accept cuckoo eggs if (1) the energetic cost of raising the cuckoois low, (2) there is time to renest, and (3) clutch size is small.We parasitized the nests of host and nonhost species with nonmimeticmodel eggs to test whether the evolution of egg recognition by cuckoo hosts could be explained by life-history variables of the host.The most significant factor explaining rates of rejection of model eggs was whether or not a species was a cuckoo host, with hostsrejecting model eggs at a higher rate than nonhosts. Egg-rejection rates were also explained by visibility within the nest and bycuckoo mass. We found little support for the life-history model of egg rejection. Our results suggest that parasitism is always suf-ficiently costly to select for host defenses and that the evolution of defenses may be limited by proximate constraints such as visibilitywithin the nest. Key words: brood parasitism, coevolution, cowbirds, cuckoos, life-history strategies.

N.E. Langmore, R.M. Kilner, S.H.M. Butchart et al., Behav Ecol 16:686-692 (2005)

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