Foods Of Stoats In North America And Eurasia

Far more has been published about the eating habits of stoats than of either of the other species. Ermine fur has long been an important but unreliable item of trade in the far north, and in North America, both the stoat and the long-tailed weasel have been trapped, skinned, and traded for many years. Scientific interest in them goes back at least to the 1920s (Seton 1926). Soviet studies on the biology of stoats date back just as far (Heptner et al. 1967). The Russian literature on stoats, and on their larger fur-bearing relatives such as sables and martens, is extensive, and some of it is now available in English (King 1975b, 1980d).

There are huge differences in mean body size of stoats living at opposite ends of their enormous geographic range (Chapter 4), and in the habitats and prey available to them. Figure 5.1 A and B show the results of a dozen studies that illustrate some ways that these adaptable little animals have responded to such variable living conditions. The smallest, North American stoats may weigh only a quarter as much as the largest stoats of the same sex in the British Isles and New Zealand, and have a totally different way of life.

On the tundra of eastern Greenland, Benoit Sittler collected stoats' scats from lemming nests (Sittler 1995; Gilg et al. 2003). When the lemming population was high, the stoats ate nothing but lemmings (Figure 5.1A, c). When the lemming population crashed, the stoats still hunted predominantly for lemmings but made up the difference with ptarmigan and ptarmigan eggs. Similarly, on the tundra-covered island of Igloolik, at 69°N off the coast of northern Canada, lemmings were at low density in the summer of 1977 when Simms (1978) collected a pile of scats and prey remains from an active stoat den (Figure 5.1A, b). Nevertheless, the stoat was still able to catch lemmings, since they made up more than three quarters of the 142 remains tallied; birds and one insect accounted for the rest. Clearly this stoat killed birds when it could in summer. As Simms pointed out, not much else was available.

The stoats studied by Lisgo (1999) in boreal forests of Alberta and by Northcott (1971) in the boreal forests of the Northwest Territories (Figure 5.1A, a) lived mainly on small rodents, which constituted roughly two thirds of the prey items killed. Males, especially, also killed some red squirrels, which weighed so much more than the small rodents that squirrels accounted for three quarters of the total weight of prey eaten (Lisgo 1999). Nonetheless, analyses of the population dynamics of stoats across northern North America show that fluctuations in their abundance follow those of voles and lemmings rather than squirrels (Johnson et al. 2000b).

Further south, stoats living in the cool temperate farmlands and forests of southern Canada and the northern United States are small in body size (Chapter 4). So, although they have a wide choice of prey, including various species of voles, mice, shrews, lagomorphs, and squirrels as well as birds, stoats in Ontario, Quebec, and New York eat mainly small rodents (Figure 5.1A, d, e, f). In Ontario, meadow voles were almost the sole item on the menu of the stoats studied by Simms (1979b) (Figure 5.1A, d), even though deer mice were also abundant. And in the alpine meadows of the Californian Sierra Nevada, remains of montane voles were practically all there was to show for an entire winter's feasting by the tiny stoats studied by Fitzgerald (1977).

Figure 5.1 (A) Some representative examples of the food habits of local populations of stoats, and a key identifying foods. (a) Northwest Territories (n = 77, Northcott 1971); (b) Northwest Territories (n = 172, Simms 1978); (c) Greenland (Sittler 1995, Gilg et al. 2003); (d) Ontario (n = 305, Simms 1979a); (e) Quebec (n = 384, Raymond et al. 1984); (f) New York (Hamilton 1933); (g) Ireland (n = 27, Fairley 1971); (h) Southern Sweden (Erlinge 1981); (i) Central European USSR (n = 1,055, Aspisov & Popov 1940); (j) the Netherlands (n = 61, Brugge 1977); (k) Switzerland (n = 690, Debrot & Mermod 1981); (l) Poland (n = 58, Jgdrzejewska & Jgdrzejewski 1998).

Figure 5.1 (A) Some representative examples of the food habits of local populations of stoats, and a key identifying foods. (a) Northwest Territories (n = 77, Northcott 1971); (b) Northwest Territories (n = 172, Simms 1978); (c) Greenland (Sittler 1995, Gilg et al. 2003); (d) Ontario (n = 305, Simms 1979a); (e) Quebec (n = 384, Raymond et al. 1984); (f) New York (Hamilton 1933); (g) Ireland (n = 27, Fairley 1971); (h) Southern Sweden (Erlinge 1981); (i) Central European USSR (n = 1,055, Aspisov & Popov 1940); (j) the Netherlands (n = 61, Brugge 1977); (k) Switzerland (n = 690, Debrot & Mermod 1981); (l) Poland (n = 58, Jgdrzejewska & Jgdrzejewski 1998).

Les Differentes Voutes

Figure 5.1 (continued). (B) Examples showing how food habits of stoats vary with changing rabbit populations and across a year. Britain, rabbits few in 1960s (n = 152, Day 1968); and after recovery of the rabbit population in the 1990s (n = 789, Springs n = 169, Summers n = 148, Autumns n = 71, Winters n = 80, McDonald et al. 2000); Italy, alpine tundra (n = 734, May n = 28, June n = 26, July n = 93, August n = 416, September n = 94, October n = 77, Matinoli et al. 2001). Prey designated as in Figure 5.1A.

Figure 5.1 (continued). (B) Examples showing how food habits of stoats vary with changing rabbit populations and across a year. Britain, rabbits few in 1960s (n = 152, Day 1968); and after recovery of the rabbit population in the 1990s (n = 789, Springs n = 169, Summers n = 148, Autumns n = 71, Winters n = 80, McDonald et al. 2000); Italy, alpine tundra (n = 734, May n = 28, June n = 26, July n = 93, August n = 416, September n = 94, October n = 77, Matinoli et al. 2001). Prey designated as in Figure 5.1A.

The much larger Eurasian stoats still take many small rodents, especially voles of the genus Microtus, but also a substantial proportion of bigger prey. A particular favorite is the water vole, Arvicola terrestris, the familiar "Ratty" of the Wind in the Willows. Both the pioneering studies on the vast Volga-Kama River flood plains of the central European USSR (Figure 5.1A, i), and more recent work in southern Sweden (Figure 5.1A, h) and Switzerland (Figure 5.1A, k) have shown how important water voles are to the feeding economy of stoats and, as a direct consequence, to their population dynamics in those areas (Chapter 10). In contrast, no water voles appeared in a small sample of stoats collected from osier beds and along the riverbanks of the low-lying Netherlands—only the occasional muskrat, an exotic species introduced from North America for fur farming (Figure 5.1A, j). Nor did the stoats in Bialowieza forest in Poland prey on water voles, but relied on smaller voles, yellow-necked mice, and amphibians (Figure 5.1A, l).

In the Italian Alps in the summers of 1996-97, small rodents were always the primary summer prey, found in 60% of 734 stoats scats collected from May to October by Martinoli et al. (2001) (Figure 5.1B). But rodents became relatively scarce in July, at the same time as fruits, mostly berries ofjuniper (Juniperus cummunis) and Vaccinium alignosa, were becoming more abundant. In August, when fruit was mature and easy to collect, these stoats incorporated fruit as over 30% of their diet. By September and October, fruit was still abundant but becoming dry and less palatable, while rodents were increasing again. Martinoli et al. concluded that the alpine stoats they observed, especially males concentrating on mate searching, minimized their foraging time by harvesting an alternative "prey," the profitable and easily available fruits, during a period of high energy demand in August, and returned to the more time-consuming rodent hunting only when the mating season was over. McDonald et al. (2000) found similar changes in diet in Britain over the seasons (Figure 5.1B).

British stoats are even larger, and small rodents seldom constitute more than a third of their diet even in lean years. Instead, their primary prey is the rabbit—at least, it was until myxomatosis arrived in Britain in late 1953 (Sumption & Flowerdew 1985). The massive population crash of rabbits throughout Britain from 1954 onward was followed by an equally massive drop in numbers of stoats (see Figure 10.2). When the first diet studies of British stoats were done in the 1960s and 1970s, both stoats and rabbits were still scarce. Nevertheless, lagomorphs (still mostly rabbits) comprised about a third of the items eaten by British stoats, and small rodents and birds another third each (Day 1968; Potts & Vickerman 1974) (Figure 5.1B). By the 1990s, British rabbits had largely recovered their numbers, both in the countryside (see Figure 10.2, inset) and on the menu of stoats. The overall diet of the 789 stoats collected in 1995-97 by McDonald et al. (2000) (Figure 5.1B) comprised 65% lagomorphs and 16% small rodents, presumably much as it had been before myxoma-tosis arrived.

Northern Ireland has no field voles or bank voles, so the only small rodents available are wood mice and house mice. Even though the stoats there are much smaller than those in Britain, they must rely on rabbits, birds, and rats at least as much as their bigger brethren, for lack of anything better (Figure 5.1A, g). In the southwest of Ireland, Irish stoats are about as large as their cousins in Britain (see Table 4.1). Sleeman (1992) collected stoat carcasses from the southern counties, and found that they also depend heavily on rabbits, despite the presence of bank voles in the southwest (introduced by at least 1964) (Fairley 1984).

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  • Luca
    Are there stoats in the united states?
    27 days ago

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