New research involving BTO provides further evidence of how humans are shaping the natural world through simple changes in our own back gardens.
Blackcaps typically visit Britain and Ireland during the spring and summer months to breed before migrating south to wintering areas in the Mediterranean. However, in recent decades, Blackcaps have expanded their wintering range northward across Europe and are now frequently found in Britain and Ireland during the winter months. These birds are not breeders staying put, but originate from breeding locations spanning a 2,000 km stretch of Europe, with birds undertaking a highly atypical north-westward migration each autumn.
This study, in collaboration with Oxford University and the Max Planck Institute, used data from colour-ringing to investigate the movements and behaviour of Blackcaps wintering in Britain and Ireland. A sample of 32 birds was also tracked with geolocators, which measure day length and the time of solar noon, and give more detailed information on birds’ movements than colour-ring sightings alone. The birds were ringed and their movements monitored by volunteers taking part in the Ringing Scheme and Garden BirdWatch.
The results showed the extent to which Blackcap ecology is shaped by human activities. The provision of bird food in gardens during cold weather has not only contributed to evolutionary change in Blackcaps, in that large numbers now migrate to Britain and Ireland for the winter, but has also modified the behaviour of the birds once they are on their wintering grounds. Blackcaps wintering in the Mediterranean primarily eat fruit and move through the landscape once their existing food supply has been depleted. In contrast, Blackcaps wintering in British and Irish gardens have a steady, predictable food supply. As a result, they move around less and are more faithful to particular wintering sites.
Access the paper: Van Doren, B.M., Conway, G.J., Phillips, R.J., Evans, G.C., Roberts, G.C.M., Liedvogel, M. and Sheldon, B.C. (2021), Human activity shapes the wintering ecology of a migratory bird. Glob Change Biol. doi.org/10.1111/gcb.15597