Avian predators and grey squirrels
In 2007 SongBird Survival commissioned its first major study. This was a correlative analysis of long term data sets seeking negative associations between predator and prey species, which could indicate causal relationships and provide a focus for more detailed work.
It took about one year to complete and was carried out by the British Trust for Ornithology (BTO) and the Centre for Research into Ecological and Environmental Modelling (CREEM) at the University of St Andrews.
Summary of Findings
There were a large number of positive associations between predators and prey, suggesting that predator numbers have largely increased as the amount of prey has increased.
For the majority of prey species examined, the study provided no evidence that songbird population changes have resulted from changes in predator numbers.
By looking at changes in predators and prey at a very large number of sites, the study identified some predator/prey relationships that may be usefully studied further.
The study indicated that studies of predation by sparrowhawks, kestrels and perhaps also grey squirrels should be priorities for future work.
Although this study found no evidence of impact of avian and grey squirrel predation on songbirds, it identified some very important areas for further research.
Crucially, SongBird Survival’s concurrent research review found that well-known national census methods like the Common Bird Census, Breeding Birds Survey and Garden Bird Feeding Survey may not be especially effective for monitoring more secretive predator species, particularly certain raptors, corvids and mammals. The same review recommended that in the UK, research should aim to assess cumulative predation impact by multiple predator species rather than a single predator species in isolation.
This suggests that more work is needed to refine study design if we are to uncover the real drivers behind continued songbird decline.
Citation: Newson, S.E., Rexstad, E.A., Baillie, S.R., Buckland, S.T. & Aebischer, N.J. 2010. Population changes of avian predators and grey squirrels in England: is there evidence for an impact on avian prey populations? Journal of Applied Ecology 47: 244- 252.
Dr Stuart Newson
Dr Newson is Senior Research Ecologist at the BTO. His work focuses on data from large national surveys of wild bird and mammal populations, particularly relating to population trend and population size estimation. His research interests include the long-term monitoring of the numbers and demography of wild bird and mammal populations, and the biology of great cormorants. He is a licensed bird ringer and UK cormorant colour-ringing coordinator.