21 May 2008
Sparrowhawk predation is not the reason for declines of some songbird species
Image: Steve Round
The populations of several common songbird species are declining across western Europe. Many people are concerned about this.
Some people blame the declines on the increase in numbers of birds of prey, particularly sparrowhawks. Some find it upsetting to see garden birds being killed by sparrowhawks and a few have called for legalised control of birds of prey to protect songbirds.
During the 1970s and 1980s, numbers of sparrowhawks – the principal avian predator of adult songbirds in the UK – increased as the species recovered from the effects of organochlorine pesticide poisoning in the 1960s.
However, the sparrowhawk population cannot increase indefinitely, because the availability of food, nesting sites and territories limits its expansion.
Indeed, the British Trust for Ornithology (BTO) Integrated Population Monitoring Programme shows that the UK sparrowhawk population has been stable since the mid-1990s.
'There is no scientific evidence that sparrowhawks or other birds of prey have had population effects on British songbirds'
If the recovery of sparrowhawks had caused songbird declines, we would expect populations of their main prey species to have decreased and those of non-prey species to have remained stable.
However, of the 16 farmland birds whose populations have declined by more than half since the 1960s, only three – house sparrow, starling and song thrush – figure prominently in the sparrowhawk’s diet. In contrast, some of the sparrowhawk’s commonest prey species, including the woodpigeon, great tit and robin, are increasing in numbers.
An extensive body of research, by the RSPB, BTO, Game and Wildlife Conservation Trust (GWCT) and many others, on declining farmland songbirds has provided no evidence that predation by sparrowhawks has driven population declines. Songbird numbers are determined by a combination of the abundance and availability of different food resources and availability of suitable breeding habitat.
In Wytham Wood, Oxfordshire, although sparrowhawks ate a large proportion of fledgling great tits and some adults, this caused no obvious reduction in breeding numbers from year to year.
When sparrowhawks were absent from Wytham Wood in the 1960s as a result of organochlorine poisoning, the breeding great tit population was about the same level as now, when sparrowhawks take large numbers of great tits.
The Government’s Raptor Working Group, which included leading experts from the GWCT, British Association for Shooting and Conservation, the Royal Pigeon Racing Association, the Scottish Raptor Study Groups and the RSPB, concluded in 2000 that:
“There is no scientific evidence that sparrowhawks or other birds of prey have had population effects on British songbirds. In our view, there is overwhelming evidence that changes in agricultural practice over recent decades have caused the substantial changes we have seen in farmland bird populations.”
The continuing decline in numbers of many songbirds is of major concern. However, while predation may under some circumstances have a localised impact on prey numbers, there is little evidence that sparrowhawks or other birds of prey have driven national declines in songbird populations.
Licensing the control of sparrowhawks or other birds of prey would not address the underlying causes of songbird decline and therefore not further their conservation. The conservation of wildlife on farmland depends on restoring features of the countryside on which songbirds depend and which have been lost as a result of modern agricultural practices.
Birds of prey should not be treated as scapegoats for wider environmental problems.