[Jonathan]

Originally Posted by david156

A lot of people class Blackcaps as a summer visitor but they are only a short distant migrant so a lot do hang around especially in the south of the country and if its not to cold there can be a lot of sightings generally. This can also happen to Chiffchaff's too, with the odd one or two staying about. I remember seeing one feeding in my garden in evergreen shrubs in January a few years ago. I was only about 3 feet away - best view of a chiffchaff i've ever had!

Hi David,

Wintering blackcaps in the UK come from Germany and eastern Europe, our own summer visitors still migrate to Spain, etc. in the autumn. This is a recent phenomenon, fifty years ago wintering blackcaps would have been rare in the UK.

Sylvia atricapilla (blackcap) breeds during the summer in Germany and, until recently, migrated to Spain or other Mediterranean areas for winter. However, studies show that 10% of blackcaps now migrate to the UK instead. To test whether this change is genetically determined or not (and, therefore, whether it could have developed by natural selection or not), eggs were collected from parents who had migrated to the UK in the previous winter and from parents who had migrated to Spain. The young were reared and the direction in which they set off, when the time for migration came, was recorded. Birds whose parents had migrated to the UK tended to fly west, wherever they had been reared, and birds whose parents had migrated to Spain tended to fly south-west. Despite not being able to follow their parents at the time of migration, all the birds tended to fly in the direction that would take them on the same migration route as their parents.

This and other evidence suggests that blackcaps are genetically programmed to respond to stimuli when they migrate so that they fly in a particular direction. The increase in the numbers of blackcaps migrating to the UK for the winter may be due to warmer winters and greater survival rates in the UK.

Cheers
Jonathan