INTRODUCTION

Among ungulates, monogamy is generally said to have evolved in a small number of species inhabiting forests or thickets (Estes, 1974; Geist, 1974; Jarman, 1974; Leuthold, 1977). In such habitats, these species have adapted to selective browsing, and their food habits have resulted in spacing, territoriality, solitary living, or living as single male-female pairs (Jarman, 1974). In those species where pair members spend comparatively long periods of time together, such as Kirk's dik-dik (Madoqua kirkii: Hendrichs & Hendrichs, 1971; Hendrichs, 1975; Tilson & Tilson, 1986; Brotherton & Rhodes, 1996; Komers, 1996; Brotherton & Manser, 1997), and the klipspringer (Oreotragus oreotragus: Dunbar & Dunbar, 1980), social monogamy has been well documented. Genetic monogamy has also been proven in Kirk's dik-dik, (Brotherton et al., 1997). However, because interactions between males and females are very rare, it has not yet been demonstrated that solitary ungulates are socially monogamous. If in fact they are socially monogamous, why do they exhibit this type of monogamy, and how do they maintain the pair bond?

Asolitary ungulate, the Japanese serow (Capricornis crispus) is a good species to use as a case study to answer these questions. The recent increase in the population of Japanese serows, which has been strictly protected in Japan since 1955, now facilitates behavioural observation in the field.