Breeding Ecology of Motacilla alba and M. grandis and their Interspecific Relationship

Abstract

The breeding season of the White wagtail Matacilla alba (from April to July) completely overlapped that of the coexisting Japanese wagtail Motacilla grandis which bred in and around towns. Both species built their nests on buildings, and some of these two species used exactly the same nest sites. Males of the White wagtail contributed to 8% of nest building, 6% of incubation, 36% of chick-feeding and 28% of faecal sac removal. These contributions were less than those of the male Japanese wagtail in incubation and chick-feeding. One of the two main food items for nestlings of both species was found to be the same, that is, the insect family Tipulidae.
Japanese wagtails obviously dominated White wagtails in the breeding season. Although the interspecific aggressiveness of Japanese wagtails towards White wagtailes was not so severe as that towards conspecifics, it was sufficient to decrease the male White wagtail's part in incubation. This aggressiveness may be a cause of habitat segregation between the two species in the overlapping part of their breeding ranges.