Home Range In Longtailed Weasels

As for stoats, the earliest data on longtail home ranges came from snow tracking. Polderboer et al. (1941) found the trails and dens of four long-tailed weasels on an Iowa farm. They reckoned that, at that time, each longtail seldom traveled more than 100 m in any direction from its primary den, so their trails rarely crossed. Each had access to as many as five or six food caches within this distance. Polderboer dug out the dens and found layers of rodent fur, skins and skulls, and heaps of scats—all the signs of an established resident weasel. But he could not make accurate estimates of the longtails' home ranges, and the assumption of a radius of movements of only 100 m seems much too low, given what we know about longtails now.

On 260 ha of farmland near Ann Arbor, Michigan, Quick (1944) mapped 52 trails made by four longtails in early 1940. He deduced that each weasel had a primary den and hunted within about 300 to 600 m of it. The average length of the 52 trails mapped was 2 km, ranging from 20 m to 5.5 km. The longtails ventured out even when the temperature was very cold (including once when it got down to -20°C), but not every night; they would sometimes stay in their dens for days. Quick calculated the areas of their home ranges assuming they were roughly circular and centered on the primary den (Table 8.1).

The ranges overlapped, but the four rarely crossed trails on the same day. When they did meet, each weasel took care to leave its mark. Once, two trails met at a post on a fence corner; each weasel deposited a scat, and then went its separate way. A month later, the trails met again at the same post, and then ran along the fence together for about 20 m. Unfortunately, snow tracking does not show whether the animals that made crossed trails actually met, nor what sex they were (but see pp. 162, 239, 286).

When Quick (1951) snow tracked long-tailed weasels in Colorado, a similar story emerged (Table 8.1). The male longtails that Glover (1942b, 1943) snow tracked in Pennsylvania went on excursions from their dens averaging 215 m in a single night (n = 11, range 18 to 773 m) and females averaged 105 m (n = 10, range 6 to 433 m). Svendsen (2003) made a passing reference to unpublished data suggesting that the average home range size in longtails is 12 to 16 ha.

The first attempt to radio track longtails was made by DeVan (1982) after he trapped seven male longtails in northern Kentucky (Table 8.1). One was trapped on two occasions, 18 months apart; this male, both times, plus one other male, was also radio tracked. The weasels hunted through the brushy overgrown vegetation along creeks and in patches of woodland, and seldom crossed open fields. Each had at least one well-hidden den.

One of DeVan's radio-tracked males was observed over 2 weeks in January-February 1975. He would come out of his den, on the bank of a dry creek, about 2 hours after sundown, and hunt up and down the creek for about 75 m each way, often revisiting the den for 2 to 10 minutes at a time during his active period of about 5 hours. The other radio-tracked male was followed over 3 months starting in November 1974. He once left his den and traveled to another den 850 m distant, robbing a baited trap on the way. Thus well supplied, he then stayed in the second den for the whole of the next day. In winter, this was a good strategy to avoid exposure to the cold.

Weasels can sometimes have the last laugh. One collared male longtail was tracked by DeVan to a burrow in an overgrown field, where he apparently stayed without moving for 3 days. DeVan grew suspicious, and finally dug out the burrow. In a grassy vole nest at the blind end he found a few drops of blood, some vole fur, and the transmitter. The weasel had gone.

DeVan caught only males, whereas Conrad Vispo (unpublished) followed a 133-g female for almost 2 months in October and November 1985 (a total of 348 tracking hours), in a nature reserve in Indiana (Table 8.1). She, too, was fairly strictly nocturnal. She nearly always came out at about sunset, around 5 p.m., and remained active until about 9 p.m. when she returned to the den and rested until about 11 p.m. After that she was active on and off for the rest of the night, especially during the last couple of hours before dawn. Unusually short excursions were often due to the weather. A heavy shower, or a passing cold front bringing a sudden drop in temperature, would drive her back to the shelter of one of her dens. During the 2 months she was located at seven different dens, all below ground and most in remnant patches of oak woodland.

The most extensive work on longtails was recently completed in rural Indiana by Gehring and Swihart (2004), who followed seven males and four females using radiotelemetry. The 200-km2 study area was agricultural (76% in agricultural fields, predominantly corn and soybeans), with patches of forest (11%), grassland (4%), and wetlands (2%). From a total of 555 radio locations, the sizes of the longtails' home ranges were estimated by making utility distributions with an adaptive kernel estimator (Seaman & Powell 1996), and an individual home range was defined as the smallest area containing 95% of the utility distribution. From these home ranges, Gerhring and Swihart analyzed how the longtails used space and how they used the available habitats, but with the same problem that Lisgo had, of failing to weight the animals' use of habitats by the time they spent in them.

The home ranges of four adult male longtails averaged 180 ha, and those of four adult females 52 ha. Three juvenile males stuck to much smaller ranges (22 ha). All these home range estimates came out smaller when calculated by the minimum convex polygon method (137, 39, and 17 ha, respectively). In general, the longtails' home ranges included the various habitat types available roughly in proportion to their area available. Within their home ranges, weasels preferred the forest patches, fencerows, and ditches, and used open fields and grasslands less. These preferences were, not surprisingly, correlated with the distribution of prey. Fencerows supported the greatest abundance and biomass of small mammals and rabbits, followed by forest patches. Forests and fencerows also had the highest counts of rabbit pellets. The longtails with the largest home ranges were those that lived where the total biomass of prey was lowest, just as do stoats. In the breeding season the males seemed to abandon their settled winter homes and range widely in search of females, just as do stoats.

Gehring and Swihart (2003) were especially interested in the responses of native predators in agricultural landscapes to the fragmentation of their habitat caused by human activities. They hypothesized, and we agree, that small mammals, even species as agile as weasels, view patches and strips of good habitat within a landscape as havens of safety in a hostile sea. The longtails used fence-rows and ditches as corridors between forest patches, because they offered good hunting and overhead cover to avoid avian predators. In that respect at least, habitat fragmentation might be viewed as a positive advantage to longtails, because such corridors become a network of connections between larger habitat patches that channel hunting weasels and their prey together. On the other hand, habitat fragmentation clearly reduces the total amount of important habitats for weasels and, therefore, reduces weasel populations. As has long been known in Britain, where the total length of hedgerows has been halved since 1945 (Robinson & Sutherland 2002), weasels really need these corridor systems and would be disadvantaged by any further homogenization of the landscape in the interests of agricultural efficiency (McDonald & Birks 2003).

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