Weasels And Wild Birds

Bird watching is an immensely popular hobby, and dozens of new books about birds appear year after year. Appeals for conservation funds do well if linked to a particularly attractive bird, at least partly because people tend to feel protective toward birds and respond quickly when birds are under threat. If the threat has reddened teeth and claws, the reaction can be extreme and sometimes irrational.

The natural history literature of North America and Eurasia provides many accounts of weasels raiding birds' nests. Weasels of all three species eat eggs and kill young and adults, especially of small species (see Figures 7.1 and 12.1). One of the earliest and clearest descriptions was given by Hussell (1974), complete with a set of four clear photographs of a stoat raiding a snow bunting nest on Devon Island in July 1969. The stoat was shown leaving the nest entrance with a chick in its jaws at 0755, 0805, 0851, and 1436 hours, and in the early afternoon of the same day a group of at least four weasels was observed in the vicinity, one of which was carrying a young bunting from this nest.

Larger birds such as ducks are not immune either. For example, Teer (1964) observed 59 nests of North American waterfowl, of which three were visited by longtails. The nests themselves were undamaged, but the eggs remaining after the weasel had left were marked with paired punctures, corresponding exactly to the size and position of a weasel's canine teeth. At Union Slough National Wildlife Refuge in Iowa, stoats and longtails were entirely responsible for 27 of 263 upland ducks' nests that failed because of predation in 1984-1985, and contributed to another 11 failures. Weasels also took eggs from at least 5 of 20 more nests that lost up to 7 eggs before the rest hatched (Fleskes 1988).

Over the six summers from 1989 to 1994, Walters and Miller (2001) monitored 239 nests of six species of woodpeckers in montane forest (1,200 m elevation) at Hat Creek in British Columbia. Of the 149 whose fate was known, 22 were destroyed by predators, including 12 (55%) by (probably) longtails. Nine of these 12 nests were concentrated within two small areas (<5 ha) within the 80-ha study area, which might have corresponded with the home ranges of two individuals that learned to spot woodpecker nests.

In two other study areas, longtails were much less often to blame for nest losses than were snakes. In Missouri, longtails contributed only one of 46 predation events on songbird nests in fields (snakes, 33), and none of 15 in forests (snakes, five) (Thompson & Burhans 2003); at Fort Hood, Texas, the predators that destroyed 48 nests ofblack-capped vireos included 18 snakes but no longtails at all (Stake & Cimprich 2003). In the Californian riparian meadows monitored by Cain et al. (2003), the nesting success of willow flycatchers was correlated with tracking activity indices of stoats.

In northern Norway, stoats are important predators of willow grouse, especially in years when rodents are scarce. Myrberget (1972) calculated the rate of predation, mostly due to stoats, over the 10 years 1960-1969. In 4 years when rodents were abundant, the average loss of eggs was 11% and of chicks 38%. By contrast, in 3 years when rodents were low, the losses of eggs reached 23%, and of chicks 54%. The worst losses were in the vole crash year of 1967, when 36% of grouse eggs were taken, and other birds suffered too. Yet, on a nearby island where there were no stoats, relatively few eggs were lost that year. In a study on a grouse moor in northern England, 45% of curlew nests and 54% of radio-tagged chicks were destroyed by stoats, even though the area was supposedly protected by year-round trapping (Robson 1998).

In the late 1940s in Wytham Wood (near Oxford), researchers from the Edward Grey Institute of Ornithology started mounting hundreds of simple

Figure 12.1 Least weasel raiding the nest of a wood thrush. (Drawn from a remote photograph by Ted Simons.)

wooden nest boxes to tree trunks for a long-term study of the great tit and the blue tit (Parus sp). When woodland rodents were scarce, common weasels often raided the boxes (see Figure 7.1). In spring, known residents often turned up in King's (1980b) live traps with yellow yolk stains all down their white chests, and eggshells and feathers were very common in their scats at that time. The damage was eventually eliminated by replacing all the boxes with freely hanging concrete tubes fitted with sloping metal caps that foiled even the agile common weasels (McCleery et al. 1996).

Natural nests are very vulnerable, especially those on the ground. To quote only one example: Clowes (1933) described how, when he was watching gulls on a rugged headland, a female stoat appeared and surveyed the scene. Satisfied, she purred, and three young appeared "as if from the earth." She found a rock pipit's nest, took a nestling and disappeared with it, returning three times and darting off again, each time with a young bird.

Similar stories are legion. In most natural communities and traditional farming areas in the mainland northern hemisphere, these losses were once sustainable over the long term. Since the advent of the intensive agribusiness school of farming, however, the economics of crop growing and livestock rearing have become skewed against wildlife, and changed the equations of life and death for wild birds, to the great alarm of conservationists. The Game Conservancy Trust (Fordingbridge, England) has campaigned against government policies that favor destructive monoculture farming at the expense of wild birds. The Trust also runs extensive education programs to help landowners meet this new emphasis on active protection of wildlife, in addition to their continued interest in game management (Tapper 1999).

Conservation of native species in Britain is now widely seen to be a vital part of game management (Reynolds & Tapper 1996; Tapper 1999). It may seem like a contradiction in terms, but it is not. Most country landowners have always had an interest in conservation, so this suggestion is seen mainly as a shift in emphasis. The Game Conservancy Trust strongly advocates a compromise policy: Run a managed estate including approved forms of predator control, on which shooting generates revenue to fund much-needed but otherwise impossible conservation policies (Reynolds & Tapper 1996).

The habitat protection and modified predator control regime that benefit contemporary game birds also benefit song birds and many other native species. The rare raptors and owls are, rightly, protected everywhere but, on the relatively wide areas of countryside represented by game estates, it is possible to reduce stoats and common weasels (plus foxes and several other common predatory species) to low density at least during the spring nesting season. All these predators are prolific generalists whose national populations are in no danger at all, but localized reduction of them could provide a significant component of a national biodiversity strategy.

To demonstrate this point, a model farm at Loddington in central England is run to show how profitable farming can be compatible with managing land both for conservation and for shooting (mainly wild-bred pheasants and hares). After 7 years of predator control and habitat improvements, several species of birds classed as "nationally declining" have increased in numbers, both over time and in comparison with neighboring farms (Stoate 2002), at a cost of less than 2% of farm profits (Tapper 1999:84).

Unfortunately, many game estates rely on releasing hand-reared birds, a policy that can still produce a shootable harvest but at minimal cost in time and effort spent on predator control. Under that strategy, fewer stoats and common weasels are killed per year than required by the Loddington model, which explains why the national bag for both species has apparently declined over the last 30 years (McDonald & Harris 1999; McDonald & Murphy 2000).

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