Blackcaps arrive in April or May and spend the summer breeding in our woodlands, parks and mature gardens. In September or October they depart for their wintering grounds in the Mediterranean and North Africa.
In the 1940s there were only a handful of blackcaps seen wintering in the UK, and most of those were in the south-west of England.
Over the years, the number has increased and spread further north. Potential explanations include milder winters or the growing popularity of providing food for winter birds.
It's now thought that several thousand blackcaps spend the winter in the UK, and we want to know how widespread they are in Wales.
This grey warbler sports a distinctive 'cap' on top of its head - black in males and chestnut in females.
In some areas of the Mediterranean, the blackcap is considered a delicacy. An estimated 900 million of these migrant birds are illegally trapped and eaten each year.
They aren't entirely safe on British shores either - domestic cats are responsible for killing 55 million birds each year.
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