(Eurasian) Siskin
Carduelis spinus

Siskins are small, seed-eating, finches that often form flocks. In Winter, you can often find them mixed with other finches, especially Goldfinches. This is a male - the females are browner and lack the black cap, which is repleaced by streaking on the head.
 

1-2: Inselspital, Bern, 18/04/2008.