Male Blackcap, Sylvia atricapilla |
When I was young, a popular ornithology trivia question was, what is the only resident British warbler? 'Resident' meaning non-migratory and remaining in Britain all year round.
The answer, found after hours of searching though my bird books, was the Dartford warbler, a very pretty little warbler found in southern England and believed to then be the only warbler to over-winter here.
That's now changed. As I witnessed last winter with one regularly coming to feed in our garden, and again a few days ago when I saw and heard one singing in a tree in my sister-in-law's garden, an increasing number of Blackcaps are now resident in Britain throughout winter, at least in Oxfordshire. There have also been numerous reports from other parts of the UK. This has led scientists to speculate that this could be the beginning of a speciation as the two populations become reproductively isolated.