Foxhunting: What limits fox numbers in Britain?
The major recorded cause of fox mortality in Britain is collision with vehicles, followed by culling. However, fox control appears to limit fox numbers only at a local level and all the studies that have looked at the effect of over-winter culling on fox densities the following spring have found culling to be ineffective in reducing the breeding population.
Two field studies, in Scotland and in Wales respectively, found that the more foxes were killed in winter, the higher the number of foxes tended to be in the following spring. Thus over-winter culling seems to be counter-productive, attracting immigrant foxes from surrounding areas. Recently, a modelling study confirmed the results of these two field studies.
A modelling study
A study used computer simulations to model the impact of different culling practices on fox numbers in a large region (1,600 km2). Of four methods of fox control (hunting with hounds, winter shooting, culling at the den and fertility control) the most effective at reducing fox populations was found to be culling at the den, which eliminates the mother with her cubs and winter shooting, which removes dispersing individuals. Both methods however, were effective only at very high culling levels (>80%), which are unfeasible for large areas. None of the methods was very effective at reducing fox numbers because immigrating foxes from other areas quickly replaced dead foxes.
Question & Answer
TopIf road collisions and culling do not, what limits fox numbers?
Foxes are organised in social groups that defend a territory against other foxes. The size of these territories is related to the availability of food both in space (how dispersed the food is) and time (according to annual/seasonal variations). As a consequence, the size of territories varies from 0.1 km2 in urban environments to 40 km2 or more in upland regions.
So, at a local level the numbers of foxes present is related to the amount and availability of food. At a local level, disease outbreaks are also likely to be an important factor in regulating fox numbers. At a national level however, food availability is unlikely to limit fox numbers. It is likely that social factors have the largest effect on regulating fox numbers at a national level.
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