Movements, Space Use and Social Organization of Radio-tracked Common Cuckoos during the Breeeding Season in Japan

Abstract

The movements, space use, and social organization of a colour-marked Common Cuckoo Cuculus canorus population were investigated during the 1984-1993 breeding seasons in central Japan. Of 333 captured cuckoos, 81 had radio transmitters attached to them. Excluding unknown birds (8.7%), the male : female ratio was 1.25 : 1.00. Radio-tracking showed that each cuckoo had a distinct breeding area and a distinct feeding area, and commuted between them every day. Birds spent most early mornings in host-rich habitats such as the Chikuma River, and then visited neighboring mountains or suburbs for foraging. The average time spent in the breeding area was 9.0 ± 0.8 hours per day (58.2 % of the daytime hours) for males and 8.7 ± 0.7 hours (56.3 %) for females. All males visited their breeding areas just after dawn, but the peak time for females was one hour later. After the early morning peak, the rate decreased gradually until early afternoon and increased again in the late afternoon with both sexes. The main activity of males in the breeding area was singing, and they sang between 19.8 % and 40.2 % of the total time they spent there. Each male sang in a restricted area and the average size of the song area was 40.9 ± 4.9 ha. However, male song areas had a large overlap, especially at the groves of acacia trees around which were many host nests. Males sometimes made short visits outside their song areas. The average size of males' breeding area, including these short visits, was 67.5 ± 8.9 ha. There were three types of females corresponding to three major hosts: the Great Reed-warbler Acrocephalus arundinaceus, the Bull-headed Shrike Lanius bucephalus and the Azure-winged Magpie Cyanopica cyana. Each female cuckoo in this study specialized on a single host species. The breeding areas of females overlapped considerably both "inter" and "intra" between different female groups. The average size of the females' breeding areas was 63.6 ± 8.5 ha. However, magpie-cuckoo females had significantly larger areas than warber-cuckoo females. The cuckoos rarely fed in their breeding areas. During their absence from the breeding area, most cuckoos visited nearby mountains, but some cuckoos, breeding at sites far from the mountains, visited suburbs for feeding. The average size of a feeding area in the mountains was 23.7 ± 5.7 ha for males and 27.6 ± 6.8 ha for females. By contrast, a female which foraged in the suburbs had a large feeding area (327.0 ha). The number of visits per day was related to the distance between the breeding area and feeding area. Cuckoos foraging at more distant sites visited these sites only once per day, while cuckoos foraging at closer sites visited them more frequently. There was a positive relationship between distance to feeding area and mean times spent per visit. There was a negative relationship between distance to feeding area and total feeding time per day. Cuckoos roosted solitarily in both their breeding and feeding areas. Roosting sites in the mountains changed almost every day, but some cuckoos roosting at the river or in the suburbs often used the same sites repeatedly. Roosting in the breeding area was more commons with males than with females, but it decreased in both sexes as the season progressed. The average size of a home range was 3.02 ± 0.28 km2 for males and 3.26 ± 0.40 km2 for females. In this paper, we discuss the following three points: (1) The separation of the breeding area and the feeding area is a common characteristic of the cuckoo and it is closely related both to the cuckoo's parasitic breeding and to its special feeding habits; (2) There are costs attendant with leaving the breeding area in order to visit a feeding area.