Activity, Survival, Independence and Migration of Fledgling Great Spotted Cuckoos

Abstract

Parental care of fledglings tends to last at least as long as that of nestlings, and in some cases twice as long (Skutch 1976). The post-fledging dependence period (hereafter called fledgling period) is critical for juvenile survival (Royama 1966, Sullivan 1989), and the probability of survival to independence appears to be an adequate estimate of relative probabilities of survival to breeding in many bird species (Magrath 1991). For avian brood parasites, very little is known about the behavior of foster parents in relation to their fledgling parasites (see review in Payne 1977 and Rothstein 1990). Only one detailed study exists (Woodward 1983), namely, on the fledging period of the Brown-headed Cowbird, Molothrus ater. Cowbirds are conspicuous after they leave the nest (Woodward 1983), in contrast to other fledgling parasites such as European Cuckoos, Cuculus canorus, which hide in the vegetation and remain immobile for long periods of time (Wyllie 1981). The Great Spotted Cuckoo Clamator glandarius is an obligate brood parasite which in Europe mainly parasitizes magpies Pica pica (Cramp 1985). We have shown that Great Spotted Cuckoo fledglings often formed flocks (group size ranged from one to five), and that every group of cuckoo fledglings was attended by a group of magpies (Soler et al., unpubl. manuscript). Cuckoo fledgling groups were frequently attended by more magpies than those involved in nestling rearing, and the feeding rate of fledgling cuckoos increased with the number of cuckoos per group and the number of adult magpies attending the group of fledgling cuckoos. We studied the behavior of fledgling Great Spotted Cuckoos. We paid special attention to the following aspects: (1) changes in the activity of fledgling cuckoos with age, (2) survival of fledgling cuckoos and magpies in parasitized nests, (3) post-fledgling dependence, and (4) migration of fledgling and adult cuckoos.