Abstract
1) Mating behaviour of the Japanese Wagtail Motacilla grandis was studied from 1983 to 1986 in Kyoto, central Japan.
2) Most male wagtails paired with only single female wagtails, but in five cases (2.2% of 225 breeding attmpts) males mated with two females.
3) Two patterns of mating process of the secondary females were observed: a widowed female stayed in her original range and mated with the neighbouring paired male; and a wandering female entered the territory held by a pair, mating with the paired male.
4) From simultaneous observation of two bigamous females, we confirmed that they spaced themselves out within the male's territory, having mutually exclusive home ranges, or that the primary female was dominant over the secondary female.
5) A bigamous male escorted and guarded his mates in rotation, and escorted the primary female longer than the secondary female.
6) The bigamous male helped little with feeding offspring of the secondary female, so that the secondary female had lower reproductive success than the primary female. This prevents bigamy in the Japanese Wagtail
