Predation and songbird populations.

Abstract

In order to consider whether the widespread declines of British songbirds may be linked with the spread of their avian predators, we provide an overview of two studies. In one, the abundance of Magpies Pica pica and Carrion Crows Corvus corone were manipulated at three farms in Leicestershire and the breeding success and abundance of songbirds was studied. In the other, extensive historical data from the Common Birds Census were used to look at whether the presence of Magpies or Sparrowhawks Accipiter nisus at individual sites affected the rates of songbird population change. In Leicestershire, songbird breeding success was higher and breeding abundance increased when corvids were controlled, although the effects of predators on the latter could not be distinguished from possible effects of habitat changes over the same period. Any local effect of Magpies on songbird breeding success did not translate into a significant effect on the rates of songbird population change at sites throughout the country. There was also no evidence that Sparrowhawks affected rates of population change. It would appear that while individual songbirds can clearly suffer from predation, the national populations are resilient. The two different approaches discussed here each have their advantages and disadvantages, and this overview highlights the benefits of combining insights from both intensive local studies and from the modelling of extensive national data.