Variation in mating behavior of sika deer: Mating behavior of sika deer on Nozaki Island

Abstract

Variation in the mating tactics of male sika deer (Cervus nippon) associated with female distribution was studied on Nozaki Island in the Goto Islands, Japan. In 1990, 1991, and 1993, observations were carried out mainly in an open grassland (about 5 ha) in the central part of the island, which was regularly used by 20 adult females and their calves for daily feeding. A majority of the observed females were not associated with other females. The estrous days of these females were not synchronous. Several females accepted multiple copulations. In the rutting season of 1991, five dominant males (DMs) established and kept exclusive home ranges, while those of subordinate males (SMs) considerably overlapped with other males. The mean home range size of dominants (4.28 ± 0.74 ha) was significantly smaller than that of subordinates (10.14 ± 0.59 ha). The open grasslands where females stayed longest when foraging during the day were occupied by dominant males, but subordinates were not chased out violently by dominants. We, therefore, designated the home range of a dominant male as dominance area. Most females copulated with dominant males. The mating success of dominants was significantly greater than that of subordinates (U = 0, p < 0.01). Frequently, dominant males did not search for estrous females, but intercepted estrous females from subordinates. The mating aggregation was formed more frequently by subordinates and might be an alternative mating tactics of subordinates. Almost all copulations were followed by guarding behavior. The postcopulatory guarding by DMs appears to be more effective in the prevention of additional female copulations with other males than guarding by SMs. Dominant males often copulated repeatedly with the same female. If the paternity of a male increases with the amount of sperm, repeated copulation seems to be an adaptation to increase his reproductive success. SMs decreased the duration of the precopulatory phase to achieve copulation before having to give way to DMs.