There is increasing awareness that changes in bird populations may be used to identify changes in the quality of particular habitats, or signal wider environmental decline. Here at the BTO we are working to understand what bird population trends from BBS data tell us about changes in the countryside.
Because of its extensive coverage across the UK, and the use of detectability which means that counts of species abundance can be used to quantify the composition of bird communities, BBS provides a fantastic resource with which to monitor environmental change. Recent analysis has indicated a general pattern for bird communities to become more similar to each other, whilst ongoing analysis will explore how well variation in bird communities reflect changes in other taxa, such as butterflies.
The rise of the generalists
BTO-led analysis published in 2011 has shown that the diversity of bird communities in the UK has increased through time. This means that we are now seeing more species on our BBS squares than we did 15 years ago. This trend appears to have been caused by population increases in a range of common and widespread species which occur across a range of habitats. At the same time, populations of more specialised species, which only occur in a small range of habitats, have tended to decline. As a result, bird communities across the UK have tended to become more similar to each other. Part of the reason for this change may be recent warming. This is not just happening in the UK, but appears to be apparent across Europe, where analyses across six European countries has found a common pattern of increasing populations of widespread generalist species relative to specialists
Davey, C.M., Chamberlain D.E., Newson S.E., Noble, D.G., Johnston, A. 2011. Rise of the generalists: evidence for climate driven homogenization in avian communities. Global Ecology and Biogeography, 21, 568-578. http://onlinelibrary.wiley.com/doi/10.1111/j.1466-8238.2011.00693.x/abstract
Le Voil, I., Jiguet, F., Brotons, L., Herrando, S., Lindström, Å., Pearce-Higgins, J.W., Reif, J., van Turnhout, C. & Devictor, V. 2012. More and more generalists: two decades of changes in European avifauna. Biology Letters in press. http://rsbl.royalsocietypublishing.org/content/early/2012/07/11/rsbl.2012.0496.abstract
Current analysis is using data on bird and butterfly communities from BBS squares where wider countryside butterfly surveys are being carried out, to test whether sites with a greater abundance or diversity of birds also support more and a greater range of butterflies. This will be an important test of the extent to which variation in the abundance and diversity of one taxa may be used to indicate patterns of environmental variation relevant to other taxonomic groups. Whilst this has been examined in other studies at relatively large spatial scales, this will be one of the first times that this has been tested at the relatively fine-scale of individual BBS squares, which is closer to the sort of scale at which the countryside is managed.