Carnivores in Northern Latitudes

The first mammals were probably nocturnal (McNab 1978; Kemp 1982) and many extant orders of small mammals have retained this trait. This behaviour is presumably due to the measure of protection from predation that darkness provides (Crawford 1934; Falls 1968; Daan and Aschoff 1982). Large, herbivorous mammals are less restricted to the nocturnal phase (e.g. Bunnell and Harestad 1990) and have been classified as `nocturnal-diurnal' (Charles-Dominique 1978). This is either because their large size renders them less vulnerable to predators, because the low energy nature of their folivorous diet demands extended periods of food consumption, or because food search time increases with increasing body size (Harestad and Bunnell 1979; Belovsky and Slade 1986). The carnivorous mammals, however, exhibit a wide diversity and flexibility of activity patterns (Kavanau 1971; Ewer 1973; Curio 1976; Daan 1981; Gittleman 1986). Peak activity times vary among the Carnivora and within individual species studied at different locations or during different seasons. For example, Mustela erminea has been described as nocturnal (Figala and Tester 1992), nocturnal in winter but diurnal in summer (Bäumler 1973; Debrot et al. 1985), crepuscular (Müller 1970) and mostly diurnal (Erlinge and Widen 1975; Erlinge 1979). The activity patterns of mammalian carnivores are influenced by a number of factors, including: diel temperature variation (Schmidt-Nielsen 1983), interference from competitors (Carothers and Jaksic 1984), limitations of the visual system (Walls 1963; Dunstone and Sinclair 1978), risk of predation (King 1975), social behaviour (Ewer 1973; Gittleman 1986), and behavioural thermoregulation (Chappell 1980). However, what makes carnivores unique is the fact that their foods, unlike that of herbivores, have their own circadian cycles of availability and vulnerability (Curio 1976; Zielinski 1986a). The foods of herbivores, although patchy in space, are relatively stable and predictable in time. Perhaps this distinction is the reason why the activity patterns of mammalian carnivores can be described so differently by different authors while the activity patterns of mammalian herbivores tend to be less