With nearly two weeks of winter behind us and a blast of cold, Arctic air dramatically influencing our weather conditions, increasing numbers of Blackcaps have been reported in local gardens over the past days. Previously dubbed ‘Central European Blackcaps’, their origins are now under scrutiny.
That Blackcaps from a breeding area in central Europe have been migrating to winter in Britain over the last sixty years has been demonstrated by ringing recoveries and is not in dispute. Nor is the fact that this population, in this short period of time, has undergone a rapid microevolution, producing genetically distinct birds with a different set of physical characteristics (see Breakaway Blackcaps).
However, in recent years a small number of recoveries indicates that some may originate much closer to home and, to complicate matters, there have been recent UK winter (November to February) recoveries of Blackcaps ringed in summer in Britain. This suggests that at least a few may have lost the migratory urge, having decided to become resident in the UK. The proportion of the summer population involved is unknown and more work needs to be done to determine if this is occurring with any regularity.
In a collaboration between Oxford University, the BTO, Exeter University and the Max Planck Institute for Evolutionary Biology, Germany to improve knowledge of migration and breeding origin, a number of wintering Blackcaps have been fitted with Geolocators. These will reveal where they have spent the summer when retrapped back at their wintering sites. To learn more about wintering behaviour, movements and use of British wintering sites, colour-ringing is also being undertaken in parallel with this study, allowing individuals to be identified by unique colour combinations. Colour-ringed Blackcaps should be reported to the BTO, via here.