The Pied Wagtail: as the name suggests, this black and white bird twitches its long tail.
The Pied Wagtail is the British subspecies of the continental White Wagtail (Motacilla alba alba). Unlike the White Wagtail, the male has a black back as well as black crown and chin/bib.
The female Pied Wagtail (above) has a charcoal grey back and flanks. She looks similar to the male White Wagtail, but the latter is a lighter grey.
Bizarrely, the Pied Wagtail's favourite habitat appears to be urban car parks (in the UK, and the White Wagtail abroad). Chins turn from black to white outside the breeding season.
They can also commonly be found by/on waterways swooping for insects.