Thousands of swallows wheel and dart around one another as they gather ahead of their epic migration to South Africa in this clip filmed in September 2014.
The unusually large gathering – perhaps as many as 30,000 birds – happened when swallows streaming down from northern parts of the UK joined those in Anglesey.
A few days later the birds had departed on their journey south for the winter, not to return to the UK’s shores until the following spring.
The clip above was first broadcast in 2014 for Autumnwatch.
Autumnwatch concludes on Thursday 5 November at 20:00 GMT on BBC Two. But you can tune in live on the website and Red Button with Unsprung, Extra and, of course, the famous webcams from 07:00 to 19:30.
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