Modern Game Estates Controlling Predator Damage Not Predators

The modern face of game preservation is very different from that of its nineteenth-century forebears. It is still a major participant sport and contributes several million pounds a year to the rural economy in Britain, even though the numbers of keepers is now less than 3,000, and the extent of the area they patrol is reduced to about 27,000 km2—about 12% of the area of Britain (McDonald & Murphy 2000).

Changes in agricultural policy since the 1970s have made the British countryside much less hospitable to wildlife of any sort (Tattersall & Manley 2003), and the large-scale "driven" shoots of Edwardian times, which relied on the millions of wild grey partridges a year bred on each estate under the protection of the gamekeepers, are just a memory. To produce enough game birds for a day's shooting, many estates simply rear large numbers of birds artificially, mostly pheasants (an introduced species in Britain) and release them shortly before the shooting season. The few gamekeepers that are left spend much less time on predator control (McDonald & Murphy 2000), so the total national tallies of stoats and common weasels killed per year are declining (Tapper 1999).

Nevertheless, some estates still take the traditional attitude and attempt to reduce the local density of all unprotected predators of game birds. Fewer than 20% of gamekeepers see stoats and common weasels as major threats now (McDonald & Birks 2003), but both are still included in routine trapping operations, at least during the nesting season. To be effective, more individuals must be removed than can be replaced, at least locally and temporarily, and that means a huge proportion of the target populations have to be removed (for common weasels and stoats at least 80%), even though those that are removed will be replaced very quickly (McDonald & Harris 2002).

Moreover, as Errington saw long ago, even this rate of removal will not have any effect on the density of residents if it only substitutes for, rather than adds to, natural mortality (Reynolds & Tapper 1996). For example, in winter when natural survival rates are low, or in autumn when dispersal is high, trapping can remove large numbers of animals without having any effect on local density. The effects of predator control are seasonal and short, but on intensively keepered estates still specializing on producing wild-bred birds (considered a more sporting target), well worth doing.

On North Farm (Sussex) most resident stoats and common weasels are removed by June. This effort achieves significant protection for game birds and their young during the critical breeding season, even though by September the predators are back, replaced by immigration from surrounding untrapped areas (Tapper 1979; Tapper et al. 1982).

The traps at North Farm are set out at the rate of 300 over 1,300 ha, that is, averaging about 200 m apart in all directions. They are placed along the hedgerows and field margins where common weasels and stoats are bound to find them. The traps are not baited, largely because the sites are so attractive; weasels in general are not only naturally curious, but they also like to keep under cover, and a good site that happens to be on a regular runway under a hedge will go on catching each successive local resident in turn.

When such a system is operated by experts, a real reduction in numbers of stoats is possible, at least while it continues (Figure 12.4). The concentration of the keeper's trapping effort in spring produces a distinct seasonal peak in the mortality rate of stoats and common weasels (see Table 11.3), although it does not necessarily increase the general level of annual mortality. Either way, the danger period has passed by June, and in any case affects mostly males. Over the course of a year, many more common weasels and stoats will be taken from an estate than could live there all at once, especially in vole peak years.

In very large areas of less accessible landscapes, where a weasel has a relatively low chance of finding a trap or being shot, attempts at "control" usually turn into harvesting, which takes a yield but does not affect density. For example, on a 50-km2 stretch of coastal sand dunes in the Netherlands, managed as a game reserve for pheasants, a force of 13 gamekeepers reaped a relatively constant harvest of stoats averaging 210 ± 32 per year, every year from 1952 to 1966. According to Heitkamp and van der Schoot (1966), about 75 stoat territories could have covered the whole reserve, on each of which an average of 4.5 young stoats might be born, giving an annual increment of about 340 stoats a year. Since the keepers removed only 62% of that number, some unknown proportion of the surplus must have been left to die naturally. A century of similar efforts on the game estates of Europe has had no long-term effects on the distribution of stoats and common weasels, for reasons easily understandable from their population biology.

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