Activity Day Or Night Hunting

Many mammals are active predominantly by day or by night, but weasels have to hunt whenever they are hungry, which is often (Zielinski 2000). This pattern may or may not be detected by studies on captive weasels, which often prefer to stay hidden until nighttime, when human disturbance around their cages has died down. Price (1971) trained least weasels and Kavanu and Ramos (1975) trained longtails to run on activity wheels, and then tested their responses to changes in how much effort was required to earn a reward. Zielinski (1986, 1988) trained both these species and also stoats, so the literature supplies information on all three species. The captive longtails and stoats were both strongly nocturnal, though willing to run by day if necessary. The least weasels were willing to run by night or day, for several sessions a day, consistent with Gillingham's (1984) conclusion that least weasels must eat several meals a day because they cannot eat enough in one meal to supply a whole day's energy needs. A few days of short rations had little effect, but weasels not fed for 24 hours more than doubled their wheel-running activity, much as wild weasels make longer hunting expeditions when voles are very scarce (Chapter 8).

Weasels can see well at any time of day or night, so in the wild their activity is governed not by their visual abilities but by a fine balance of conflicting needs: to find food sufficient to maintain their galloping metabolism, to find mates or feed their young, and at the same time to avoid their two worst enemies, cold weather and larger predators.

Raptors, owls, and foxes are a constant danger, and weasels adjust their foraging schedules in response (Zielinski 1988). For example, common weasels were easier to trap during the day than at night in Wytham Wood, in England, where danger from humans during the day was probably lower than that from tawny owls at night (King 1975c). Morning and evening trap records are only a rough method of estimating activity even when corrected for changing day length, so these data were enough only to show that King's original assumption, that the weasels would be mainly nocturnal, was wrong. Years later, Macdonald et al. (2004) made another study of the Wytham weasels, mainly on arable farmland on a different part of the estate. They confirmed, from data that were vastly more accurate but collected over a much shorter period, that the seven males and three females they radio tracked were exclusively diurnal. In Bialowieza Forest, east ern Poland, and in Kielder Forest, northern England, places where common weasels have to dodge the attention of tawny owls, foxes, and many other nocturnal hunters, they are also mainly diurnal (Jgdrzejwski et al. 2000; Brandt & Lambin 2005).

Cold winters are a time of serious risk for weasels, and in all northern continental climates weasels absolutely depend on access to a well-insulated den (Chapter 7). This restriction is one of the costs of being a long thin animal (Brown & Lasiewski 1972) in a cold climate, and has more to do with thermoregulation than with hunting strategy. Weasels cannot lay down fat or hibernate (Chapter 2); they can best defend themselves from chilling by staying in their dens and feeding from their cache of stored prey, so that on the coldest or wettest days they can avoid going out at all.

The total activity budget of the Quebec stoats was correlated primarily with ambient temperature, and secondarily with reproductive condition (Robitaille & Baron 1987). Outside the breeding season, there was a strong correlation between air temperature and the periods that these animals were willing to spend outside their dens. The same correlation was observed in wild, radio-collared longtails in Kentucky by DeVan (1982), and in radio-collared common weasels in Poland by Jgdrzejwski et al. (2000). The Polish weasels actively hunted for an average of 2 to 6 hours a day, depending on the season, and spent almost all night in their dens. Their hunting trips were always short, most less than 2 hours at a time, but they made many more trips on warm days (>10°C) than cold days (down to -5°C). Variations in temperature were much more important in determining the lengths of hunting trips of the Polish weasels than was the density of rodents, at least over the normal range.

In a milder climate, thermoregulation is less of a problem, so individual activity patterns can be more variable. Stoats radio tracked in temperate southern Sweden divided their lives into a pattern of alternating periods of hunting, eating, and resting around the clock. They were seldom out of their dens for more than 10 to 45 minutes at a time in any season (Erlinge 1979b), totalling 6 to 9 hours per day. In New Zealand, 11 stoats tagged with activity-sensitive transmitters were usually active for at least 40 minutes at a time, totaling an average of about 8 hours a day at all seasons (R. Martin & M. Potter unpubl.). Of the 896 hours of activity data logged during this study, two thirds was recorded during the day, depending on the season, but there was huge variation between the individuals. Some ignored cool temperatures and rain, others avoided them, and this high individual variability meant that, at least in that study area, there were no times or conditions that were better than any others for maximizing trapping success.

One would expect weasels to be less active when the density of prey is very high, because easy hunting allows smaller home ranges and shorter hunting expeditions, leaving more time to rest and stay out of danger in a den—or, in the right season, for interactions with other weasels. In summer in Québec at a time when voles were abundant, the stoats watched by Samson and Raymond (1995) made an average of five expeditions averaging 40 minutes long during the day, and one at night. In total they spent an average of only 5 hours out of their dens each day, perhaps because the study was done after the mating season. By contrast, in one summertime study in northern England, common weasels were more active in habitats with very high vole numbers, rather than less (Brandt & Lambin 2005). In Québec, stoats are about the same size as common weasels in northern England, and the summers are warmer, so why the difference? One possible explanation is that common weasels, unlike stoats, can produce a second litter in summers when food is abundant (Chapter 9), and a second breeding cycle demands a lot of extra activity by males searching for mates and by females hunting for their young. Brandt and Lambin's study fits neatly with other evidence of extended breeding by common weasels in vole peak years (McDonald & Harris 2002).

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