House martin (Delichon urbicum)

CC-BY Kostis Tzortzakakis

Looks like
The house martin has a short and slightly forked tail. Its back and head have a dark blue colour. The region around the base of the tail is white, while the tail itself is also dark blue. It often flies high and can be readily distinguished on the basis of is short tail and the white region at the tail base. It has a short, thin beak with which it snatches insects from the air.
Where and when to spot it
It constructs a closed nest of clumps of clay which it transports in its beak. It builds its nest on walls under balconies, close to windows of large buildings, under bridges, etc. It arrives in Europe in early spring and leaves again in autumn to overwinter in Africa.