Linnet

"A small, slim finch, widely distributed, and once very popular as a cage bird because of its melodious song. Males are attractively marked with crimson foreheads and breasts, females much browner. It has an undulating flight, usually twittering as it flies and may be seen in large flocks during the winter.

Linnet numbers have dropped substantially over the past few decades, with the UK population estimated to have declined by 57 per cent between 1970 and 2008. Recent Breeding Bird Survey results suggest that while populations in England and Wales continue to decline, those in Scotland and Northern Ireland are currently increasing."

http://www.rspb.org.uk/wildlife/birdguide/name/l/linnet/index.aspx