Weasels and Martens — Carnivores in Northern Latitudes

Abstract

The first mammals were probably nocturnal (McNab 1978; Kemp 1982)andmany extant orders of small mammals have retained this trait.This behaviour is presumably due to the measure of protection frompredation that darkness provides (Crawford 1934; Falls 1968; Daanand Aschoff 1982). Large, herbivorous mammals are less restrictedto the nocturnal phase (e.g. Bunnell and Harestad 1990) and havebeen classified as `nocturnal-diurnal' (Charles-Dominique 1978).This is either because their large size renders them less vulnerableto predators, because the low energy nature of their folivorous dietdemands extended periods of food consumption, or because food searchtime increases with increasing body size (Harestad and Bunnell 1979;Belovsky and Slade 1986). The carnivorous mammals, however, exhibita wide diversity and flexibility of activity patterns (Kavanau 1971;Ewer 1973; Curio 1976; Daan 1981; Gittleman 1986). Peak activitytimes vary among the Carnivora and within individual species studiedat different locations or during different seasons. For example,Mustela erminea has been described as nocturnal (Figala and Tester1992), nocturnal in winter but diurnal in summer (Bäumler 1973; Debrotet al. 1985), crepuscular (Müller 1970) and mostly diurnal (Erlingeand Widen 1975; Erlinge 1979). The activity patterns of mammaliancarnivores are influenced by a number of factors, including: dieltemperature variation (Schmidt-Nielsen 1983), interference from competitors(Carothers and Jaksic 1984), limitations of the visual system (Walls1963; 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 factthat their foods, unlike that of herbivores, have their own circadiancycles of availability and vulnerability (Curio 1976; Zielinski 1986a).The foods of herbivores, although patchy in space, are relativelystable and predictable in time. Perhaps this distinction is the reasonwhy the activity patterns of mammalian carnivores can be describedso differently by different authors while the activity patterns ofmammalian herbivores tend to be less variable. If small carnivoresfeed on different proportions of prey types in different locales,each with different circadian phases of maximum vulnerability, wewould expect considerable intraspecific variation in modal activitytimes. How the circadian rhythms of prey vulnerability influencepredator activity will be a central issue of this review. Mustelidsare the most ecologically diverse family within the Carnivora (Wozencraft1989), including dietary specialists and generalists that range fromstrictly carnivorous to omnivorous. The subfamily Mustelinae (e.g.weasels, mink, polecats, ferrets, martens, sable, fishers) originatedin the Miocene (Martin 1989; Anderson 1994) and the earliest formsoccupied forest habitats and probably lived in much the same waymartens do today. During the Plio-Pleistocene the cooler, drier climatefavoured the establishment of grasslands and small mammals, especiallyvoles ( Microtus spp.), began to radiate into forms that occupiedthe forest-steppe environment (Webb et al. 1983; Martin 1989 ). Althoughthe genus Martes was clearly defined by this time, intermediatesbetween Martes and Mustela were becoming established (Anderson 1970).The development of the grassland biome provided opportunities forpredators that were small enough to pursue voles and lemmings ( Dicrostonyxspp., Lemmus spp.) in their burrows, tolerate the fluctuation inprey numbers typical at northern latitudes, and sustain themselvesthrough the harsh winters (King 1989).