David Tipling / House Martin (Delichon urbicum) leaving nest under eaves of house, Northumberland, UK, July

Sven Zacek,Sven Zacek / House Martin (Delichon urbicum) in flight. Jogevamaa county, Estonia, July.

Oscar Dewhurst / House martins (Delichon urbicum) collecting mud from puddles for nest-building. March. Donana National Park, Spain. March.

Nick Upton / House martins (Delichon urbicum) flying up to and perching on bricks under house eaves as a group gathers ahead of their autumn migration, Gloucestershire, UK, September.

Nick Upton / House martins (Delichon urbicum) perching on bricks under house eaves as a group gathers ahead of their autumn migration, Gloucestershire, UK, September.

Nick Upton / Swallow (Hirundo rustica) group and a House martin (Delichon urbicum) perched on power lines gathering ahead of their autumn migration, Gloucestershire, UK, September.

David Perpinan / Two Common house martins (Delichon urbicum) fly out of artificial nest, Barcelona, Spain, April.

David Perpinan / Group of Common house martins (Delichon urbicum) fighting over a nest, Barcelona, Spain, June.

David Perpinan / Common house martin (Delichon urbicum) entering nests, flying against sky, Barcelona, Spain, June.

David Perpinan / Magpie (Pica pica) perched on window ledge while Common house martin (Delichon urbicum) fly around it, Barcelona, Spain, June.

David Perpinan / Common house martin (Delichon urbicum) flying into nest before deterring and flying after an intruder, Barcelona, Spain, June.

David Perpinan / Common house martin (Delichon urbicum) repairing nest damaged by bad weater, while another bird feeds chicks in neighbouring nest, Barcelona, Spain, June.

David Perpinan / Common house martin (Delichon urbicum) feeding chicks in a nest damaged by bad weather, Barcelona, Spain, June.

David Perpinan / Common house martin (Delichon urbicum) repairing nest damaged by bad weater, Barcelona, Spain, June.

David Perpinan / Group of Common house martin (Delichon urbicum) collecting mud for their nests, Barcelona, Spain, May.

David Perpinan / Group of Common house martin (Delichon urbicum) collecting mud for their nests, Barcelona, Spain, May.

David Perpinan / Group of Common house martin (Delichon urbicum) collecting mud for their nests, Barcelona, Spain, May.

David Perpinan / Group of Common house martin (Delichon urbicum) and Barn swallows (Hirundo rustica) collecting mud for their nests, Barcelona, Spain, May.

David Perpinan / Group of Common house martin (Delichon urbicum) collecting mud for their nests, Barcelona, Spain, May.

David Perpinan / Common house martin (Delichon urbicum) building nest, Barcelona, Spain, May.

David Perpinan / Common house martin (Delichon urbicum) collecting mud for nests, together with Barn swallows (Hirundo rustica), Barcelona, Spain, May.

David Perpinan / Common house martin (Delichon urbicum) flying against blue sky, Barcelona, Spain, June.

David Perpinan / Common house martin (Delichon urbicum) flying against blue sky, Barcelona, Spain, June.

David Perpinan / Common house martin (Delichon urbicum) hovering in slow motion in front of the camera with the skyline of a city behind, Barcelona, Spain, June.

David Perpinan / Common house martins (Delichon urbicum) perched on wire during migration, Cuenca, Spain, August.

David Perpinan / Common house martins (Delichon urbicum) visiting nests, Barcelona, Spain, May.

David Perpinan / Common house martin (Delichon urbicum) in nest, Cuenca, Spain, June.

David Perpinan / Pair of Common house martins (Delichon urbicum) visiting and leaving nest, Cuenca, Spain, June.

David Perpinan / Two Common house martin (Delichon urbicum) nests in the corner of a window, while birds fly in the background Barcelona, Spain, May.

David Perpinan / Common house martins (Delichon urbicum) mating inside a nest under construction, Barcelona, Spain, April.

David Perpinan / Common house martin (Delichon urbicum) leaving nest, Barcelona, Spain, June.

David Perpinan / Common house martin (Delichon urbicum) using mud to build a nest, Barcelona, Spain, April.

David Perpinan / Pair of Common house martins (Delichon urbicum) interacting inside a nest under construction, Barcelona, Spain, April.

David Perpinan / Common house martin (Delichon urbicum) feeding chicks with in a semi-destroyed nest due to bad weather. Another bird feeds chicks in the neighbour nest, Barcelona, Spain, June.

David Perpinan / Juvenile Common house martin (Delichon urbicum) perched on a cable, Cuenca, Spain, August.

David Perpinan / Common house martin (Delichon urbicum) pair in a nest, Cuenca, Spain, July.

David Perpinan / Group of Common house martins (Delichon urbicum) resting under cover while it rains, Cuenca, Spain, August.

David Perpinan / Two Common house martins (Delichon urbicum) on autumn migration resting under a roof, Cuenca, Spain August.

David Perpinan / Group of Common house martins (Delichon urbicum) perched together on cables before all taking off, Cuenca, Spain, August.

David Perpinan / Group of Common house martins (Delichon urbicum) perched around a nest, Cuenca, Spain, August.

David Perpinan / Group of Common house martins (Delichon urbicum) perched on cables, Cuenca, Spain, August.

David Perpinan / Group of Common house martins (Delichon urbicum) perched on a cable, Cuenca, Spain, August.

David Perpinan / Common house martins (Delichon urbicum) perched on cables, Cuenca, Spain, August.

David Perpinan / Common house martins (Delichon urbicum) perched on cable, Cuenca, Spain, August.

David Perpinan / Wide shot of Common house martins (Delichon urbicum) gathering in village for Autumn migration, Cuenca, Spain, August.

David Perpinan / Common house martins (Delichon urbicum) perched on a cable, Cuenca, Spain, August.

David Perpinan / Group of Common house martins (Delichon urbicum) preening on cable, Cuenca, Spain, August.

David Perpinan / Common house martin (Delichon urbicum) perched on a cable and then flies away, Cuenca, Spain, August.