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.
The vocalization of the Japanese wagtail was classified into location call, warning call, threatening sound and song, each being composed of basic sounds and phrases. The epigamic behavioural sequence to copulation was related to the following behaviours: Femaleappeasement display, flying courtship display and repelling; Male-courtship display, bill opening and back showing. Aggressive behaviours (chasing, threatening and physical combat) were most frequently observed between the same sexes. The most intensive exclusiveness was also seen between the same sexes showing the above aggressive behaviours. Spatial relationships between the song and two aggressive behaviours (chasing and threatening) were interpreted in relation to 1) the area which an owner tried to occupy, 2) the dominance relationship between the owner and others which tried to intrude, and 3) the aggressive area where the owner's aggressiveness existed. The border line of territory as "any defended area" was defined here as the outer limit of aggressive area where the neighbour was absent and as the positions of mutual threatening where the neighbour existed.
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