The effect of an experimental reduction in predation pressure on the breeding success and population density of grey partridges Perdix perdix.
1. A 6-year experiment is described which was designed to test whether or not predation control, as practised by traditional and currently legal methods, increases (i) the breeding success and autumn numbers of partridges, and (ii) the subsequent breeding density.
2. In the experiment, predation control effort was highly seasonal and designed to reduce partridge breeding season losses by killing resident predators of selected species.
3. The predation control significantly reduced the abundance of foxes, carrion crows and magpies during the critical partridge nesting period.
4. After the nesting period, predators re-established themselves each year, during late summer and early autumn.
5. The predation control significantly increased the proportion of partridges that bred successfully and the average size of their broods, thus substantially improving the production of young. Excluding effects of site and year predation control increased August numbers by 75%. Incorporating the effects on breeding stocks in subsequent years this led to an overall 3.5-fold difference between autumn populations with and without predation control.
6. Predation control significantly increased partridge breeding stocks the following year. Breeding stocks in years following predation control were 36% larger than stocks in years that did not follow predation control - excluding the effects of year and site. After 3 years this had produced a 2.6-fold difference in breeding density between the sites with and without predation control.
7. These results suggest that predators play a key role in limiting production and subsequent breeding density of partridges.