Small Mammals

Weasels on the hunt run from one patch of cover to the next, investigating every small hole and occasionally listening and looking around from a vantage point, testing the wind. Their habit of sitting up on their hindquarters is an obvious way of overcoming the disadvantages of having such short legs, and the Germans have coined an expressive phrase describing it: "er macht Mannchen" ("he becomes a little man"). Weasels search for prey using smell, hearing, and sight, probably in that order (Gillingham 1986). They can smell out the exact routes where voles and mice have traveled, and they are alert to the slightest sound. Weasels systematically search the forest floor, snooping along logs and under fallen branches, checking around the trunks of trees and exploring roots to find holes, and entering cavities and crevices up trees. Sometimes a weasel will dig to enlarge a hole, or locate a rodent by sniffing or listening. The weasels watched by Jgdrzejwska and Jgdrzejwski (1998) explored on average 26 holes per kilometer of foraging.

All weasels tend to intersperse foraging expeditions with periods of rest (Erlinge 1979b; Sandell 1988; Zielinski 2000). They may hunt for less than an hour, or for several hours, then return to a den. In winter, they often sleep most of the night, while in summer, females with growing young forage almost incessantly. All of the weasels can travel up to 2 km in a single trip of a few hours, especially when food is scarce, but in times of plenty they may travel only a few hundred meters on each hunting trip.

Weasels are good swimmers (Sleeman 1989b) and can reach inshore islands at least 1.5 km from a mainland shore. From eyewitness accounts, and from the distribution of stoats on offshore islands, it is quite certain that a stoat can easily reach islands within that distance of the mainland (King & Moors 1979a;

Taylor & Tilley 1984). The swimmer cannot know whether the effort is going to be worthwhile, although sometimes it is lucky. G.C. Phillips watched a stoat swimming "a determinedly straight course" for some 400 m to an island in Baltimore Bay (southwest Ireland) that still had healthy rabbits after the mainland stock had been virtually wiped out by myxomatosis (unpublished observation quoted by King & Moors 1979a). On the other hand, the stoat seen by Morton Boyd (1958) on Eilean Molach, 200 m from the shore of a Scottish loch, would not have stayed long on an islet of less than a tenth of a hectare.

In Finland, stoats move frequently among the thousands of inland islands (Heikkila et al. 1994), which provide patches of high prey density and set the scene for a hide-and-seek drama between stoats and voles. In New Zealand, three radio-collared stoats regularly visited both sides of a fast-flowing river and could only have crossed it by swimming (Murphy & Dowding 1994). In Wyoming, R.A. Powell (unpubl.) has followed tracks in the snow that crossed cold, swiftly flowing streams and small rivers even when the air temperature was far below freezing.

Weasels concentrate their hunting in the habitats where they know, perhaps from experience, that they are most likely to find prey (Nams 1981). The favorite hunting grounds where a resident weasel will spend almost all its time often comprise less than half the area of its home range. In snow, the track of a hunting weasel zig-zags this way and that, missing nothing of interest (Powell 1978a, 1978b). A thick covering of snow protects small rodents from most predators, but not from weasels. Tracks frequently dive under the snow into the hollows at the roots of trees, through the loose snow under protruding branches, and down natural fissures in the snow cover beside logs (Figures 6.1 and 6.2). For example, the tracks of the stoats studied by Edwards et al. (2001) twisted and turned through areas with vegetation low to the ground and where coarse woody debris, saplings, and trees protruded from the snow.

The tracks often pop back up above the snow elsewhere. If a snow crust is buried beneath the surface, the weasel can get no further down, but will move along the covered crust, pushing up the new snow with its back and making characteristic bulges, like those above moles' tunnels. A captive weasel will burrow in leaves or peat the same way.

Weasels forage most widely when prey populations are decreasing (Jgdrzejwska & Jgdrzejewski 1998; Klemola et al. 1999). Tracks in the snow suggest that large weasels travel longer distances than small weasels, which implies that, on the average, the larger (or largest) species living at any site forages more widely than the smaller, and that males forage more widely than females. Yet, the broad overlap in paw sizes, track patterns, and bounding distances among the species and between the sexes makes absolute identification of a track impossible.

Voles make extensive tunnels through the grass and moss under the snow, and weasels are the supreme experts at tunnel hunting. The smaller ones tend to be exactly the right size for getting into the tunnels of the local voles. In

Figure 6.1 Weasel tracks in snow zig-zag back and forth and often dive under the snow. These erratic travel patterns show that weasels inspect everything of interest, but the zig-zags and dips also make movements of weasels unpredictable, thereby making the weasels hard for other predators to catch.

Ontario, Simms (1979a) calculated that small female stoats could get into over 90% of subnivean vole tunnels (22 to 28 mm diameter) and male stoats and female longtails could get into over 70%. The small Canadian stoats whose stomachs were examined by Northcott (1971) had made a speciality of digging fat jumping mice (Zapus) out of their winter hibernation nests.

Female common weasels in Scotland can run easily through all but the very smallest vole burrows (averaging 23 mm diameter) and males can get through the largest with a squeeze (Pounds 1981). That most males can squeeze through most vole tunnels is critically important, because pregnant female stoats and weasels (and presumably longtails as well) average the same diameter as adult males (Gliwicz 1988).

The largest weasels are excluded from vole tunnels (Simms' male longtails could get into only 10% of them) but freely enter the wider tunnels of ground

Figure 6.2 The northern weasels are small enough to hunt a vole through its under-snow tunnels and to follow it into its last refuge.

squirrels, chipmunks, rabbits, and water voles. Mole runs (see Figure 8.4) are easily accessible and often used, especially as they usually lead to a large, warm, and comfortable nest (Chapter 11). At dusk one evening, Florine (1942) set two traps at the entrance of a pocket gopher burrow, so that only animals coming from within would be caught. By 9 p.m. one of them held a pocket gopher, and the other a long-tailed weasel. Likewise, in July 1930 at Milner Pass, in the Rocky Mountains National Park, Colorado, Dixon (1931) watched a stoat chasing pikas. It could get into any space between rocks that the pikas could, and just as fast. It followed by scent the winding course taken by the pika with ease and accuracy. Other pikas joined in as the first ones got tired. It was almost as if the pikas were cooperating, forcing the weasel to run a relay race against overwhelming numbers of opponents.

Weasels have no difficulty killing small rodents in confined spaces. Weasels that each of us has kept in captivity could kill voles and house mice in narrow tunnels. The radio-collared weasels observed by Jgdrzejwski et al. (1992) hunted during the day, systematically searching underground dens and tunnels of rodents, and cavities 1 to 4 m up old trees. The strictly nocturnal yellow-necked mice were especially vulnerable in cold weather, because then they saved energy by retreating to their nests and falling into short periods of torpor—not a true hibernation, but a sleep deep enough to make them defenseless against an intruding weasel.

On the other hand, if the potential victim is already alert, and especially if it is relatively large, the risk of injury is real, and the weasel does not always come off best. When Durward Allen (1938b) paired long-tailed weasels with cottontail rabbits in a cage, the weasel killed the rabbit in half the trials, but the rabbit killed the weasel in the other half. A cage is clearly an artificial place for a weasel and rabbit to meet, yet wild weasels do find and attack rabbits in confined places, and must sometimes be unlucky.

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