Effects of brood parasitism by the Great Spotted Cuckoo on the breeding success of the Magpie host: An experimental study

Full article

Published:

Volume 43(1), June 1996. Pages 87-96.

Language:

English

Keywords:

Brood parasitism, Clamator glandarius, host breeding success, Pica pica.

Abstract:

Brood parasitism by the Great Spotted Cuckoo Clamator glandarius strongly influences the breeding success of its Magpie Pica pica host. Hatching, fledging and breeding success of the Magpie in parasitized nests were significantly lower than in nests not parasitized. Most parasitized nests produced no Magpie chicks. On average, only 0.6 magpie chicks fledged per parasitized nest. The reproductive failure of the Magpie was due to both egg destruction by adult cuckoos and nestling cuckoos outcompeting Magpie chicks. Two experiments were carried out to determine the separate effects of the parasite female and the parasite chick on the breeding success of the Magpie both when the parasite egg was laid early and late in the Magpie laying sequence. In the first experiment? in which we simulated the late laying of a parasite egg, we found that the difference between breeding success in unparasitized and naturally parasitized nests was due entirely to egg destruction by adult Great Spotted Cuckoos. In the second experiment, where we simulated early laying of the parasite egg, the main difference between breeding success in unparasitized and naturally parasitized nests was due to the higher competitive ability of cuckoo nestlings. By comparing the number of chicks fledged in experimentally parasitized nests (without parasite egg destruction) in both experiments, we found that the negative effect of the cuckoo chick on the Magpie nestlings was considerably higher when the egg was laid early than when it was laid late in the magpie laying period.