Laurie Campbell / Northern gannet (Morus bassanus) gathering nesting material, Bass Rock, Firth of Forth, East Lothian, UK, July

Marie Read / American Cliff Swallows (Petrochelidon pyrrhonota) forced copulation attempt at muddy puddle where they are gathering mud as nesting material. Mono Lake Basin, California, USA, June.

Marie Read / American Cliff Swallows (Petrochelidon pyrrhonota) forced copulation (attempt at muddy puddle where they are gathering mud as nesting material. Mono Lake Basin, California, USA, June.

Marie Read / American Cliff Swallows (Petrochelidon pyrrhonota) forced copulation attempt at muddy puddle where they are gathering mud as nesting material. Mono Lake Basin, California, USA, June.

Tui De Roy / Red-footed booby (Sula sula) gathering nesting material. Darwin Bay, Genovesa (Tower) Island, Galapagos, Ecuador, June.

Charlie Summers / Southern Ground hornbill (Bucorvus leadbeateri) gathering nesting material in a riverbed in Lake Manyara National Park, Tanzania

Charlie Summers / Southern Ground hornbill (Bucorvus leadbeateri) gathering nesting material in a riverbed in Lake Manyara National Park, Tanzania

Loic Poidevin / Madagascar magpie robin (Copsychus albospecularis) female on ground collecting nesting material, Madagascar.

Alan Williams / Pair of Jackdaws (Corvus monedula) collecting mud for nest building, North Wales, UK, May 2010

Alan Williams / Jackdaws (Corvus monedula) collecting wool for nest material, North Wales, UK, April 2010

Roger Powell / White Stork (Ciconia ciconia) gathering nesting material from an old straw bale, Castro Verde, Portugal, April

Roger Powell / Calandra Lark (Melanocorypha calandra) female gathering nesting material in meadow, Castro Verde, Portugal, April

Fabio Liverani / Chaffinch (Fringilla coelebs tintillon) female gathering nesting material, Garajonay National Park, La Gomera, Canary Islands, Spain

Donald M. Jones / American Robin (Turdus migratorius) gathering nest material, northwest Montana

Stephen Dalton / House martins {Delichon urbicum} gathering nesting material from lawn, UK

Alan Williams / Kittiwakes (Rissa tridactyla) gathering nesting material from a farm field close to breeding cliffs, Fowlsheugh RSPB Reserve, Aberdeenshire, UK, May

Alan Williams / Black-headed gull (Chroicocephalus ridibundus) gathering nesting material, Minsmere RSPB Reserve, Suffolk, UK, May

John Cancalosi / Cactus Wren (Campylorhnchus brunneicapillus) gathering nest material, Arizona, USA

John Cancalosi / Cactus Wren (Campylorhnchus brunneicapillus) gathering nest material, Arizona, USA

John Cancalosi / Cactus Wren (Campylorhnchus brunneicapillus) gathering nest material, Arizona, USA

Ingo Arndt / Alpine Marmot (Marmota marmota) gathering grass for nesting material, Hohe Tauern National Park, Austria

Flip de Nooyer / Northern Gannet (Morus bassanus) flying with nesting material, Canada

Sumio Harada / Red Squirrel (Tamiasciurus hudsonicus) climbing tree with nesting material in mouth, Rocky Mountains, North America