Florian Möllers / Mallard (Anas platyrhynchos), female nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Photographer Florian Mollers having breakfast beside a female Mallard (Anas platyrhynchos) nesting in window box of a 4th floor flat, Berlin, Germany, June. Model released

Wild Wonders of Europe / Varesvuo / Red-footed falcon (Falco vespertinus) male at nesting box in Hortobagy NP, Hungary, May 2008

Flip de Nooyer / Eurasian Kestrel (Falco tinnunculus) group of five juveniles in nesting box, Europe

Fabrice Cahez / Eurasian Hoopoe (Upupa epops) arriving at nest box with invertebrate prey. Vosges, France, June.

David Woodfall / Sessile oak (Quercus petraea) nesting box sited to encourage nesting Pied flycatchers, Gilfach Nature Reserve, Radnorshire Wildlife Trust, Powys, Wales, UK May

David Woodfall / Sessile oak (Quercus petraea) nesting box sited to encourage nesting Pied flycatchers, Gilfach Nature Reserve, Radnorshire Wildlife Trust, Powys, Wales, UK May

David Woodfall / Ancient Sessile oak (Quercus petraea) with bird box, placed by Wildlife Trust for nesting Pied Flycatchers (Musciapa hypoleuca), Gilfach Nature Reserve, Radnorshire Wildlife Trust, Powys, Wales, UK Ma...

David Woodfall / Ancient Sessile oak (Quercus petraea) with bird nest box, placed by wildlife trust for nesting Pied Flycatchers (Musciapa hypoleuca), Gilfach Nature Reserve, Radnorshire Wildlife Trust, Powys, Wales,...

Tom Vezo / Mountain Bluebird (Sialia currucoides) male at nest box, British Columbia, Canada

Kim Taylor / Red mason bee (Osmia rufa) female laying egg on pollen / nectar mix in egg cell of artificial bee nesting box, Surrey, UK, April

Kim Taylor / Red mason bee (Osmia rufa) female exiting tube in order to turn around and enter tail first to off-load pollen into cell in artifical bee nesting box, Surrey, UK

Kim Taylor / Red mason bee (Osmia rufa) female in flight carrying pollen and flower nectar to nest in artifical bee nesting box, Surrey, UK, April

Kim Taylor / Red mason bee (Osmia rufa) female in flight carrying mud to nest in artificial bee nesting box, Surrey, UK, April

Kim Taylor / Red mason bee (Osmia rufa) female building pollen retaining wall of mud and sand to separate egg cells in artificial nest box, Surrey, UK, April

Roland Seitre / Veterinarian Mar Carascos reaching into a nesting box to inspect a young Yellow-shouldered Amazon (Amazona barbadensis). Isla Margarita, Nueva Esparta, Venezuela, 2007.

Roland Seitre / Artificial nesting box used for rearing Yellow-shouldered Amazons (Amazona barbadensis). Isla Margarita, Nueva Esparta, Venezuela, 2007.

Ernie Janes / Great spotted woodpecker (Dendrocopus major)pecking at the wood of a nesting box, UK

Ernie Janes / Great spotted woodpecker (Dendrocopus major)pecking at the wood of a nesting box, UK

Peter Cairns / Pine Marten (Martes martes) on roof of Goldeneye (Bucephala clangula) nesting box. Cairngorms National Park, Scotland, August.

Florian Möllers / Mallard (Anas platyrhynchos), female nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Mallard (Anas platyrhynchos), female nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Woman rescues the duckling of a Mallard (Anas platyrhynchos) nesting in window box of a 4th floor flat, female duck watching, Berlin, Germany, June

Florian Möllers / Mallard (Anas platyrhynchos), female nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Mallard (Anas platyrhynchos), female nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Two women rescue the ducklings of a Mallard (Anas platyrhynchos) nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Mallard (Anas platyrhynchos), female nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Man photographing a female Mallard (Anas platyrhynchos) nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Woman rescues the duckling of a Mallard (Anas platyrhynchos) nesting in window box of a 4th floor flat, Berlin, Germany, June

Florian Möllers / Man taking photo with mobile phone of female Mallard (Anas platyrhynchos) nesting in window box of a 4th floor flat, Berlin, Germany, June

Luciano Candisani / Hyacinth Macaw (Anodorhynchus hyacinthinus) emerging from nest box installed by researcher Neiva Guedes, Pantanal, Brazil

Luciano Candisani / Hyacinth Macaw (Anodorhynchus hyacinthinus) emerging from nest box installed by researcher Neiva Guedes, Pantanal, Brazil

Charlie Summers / Western bluebird (Siala mexicana) flying to nesting box with food for chicks, USA

Roger Powell / Common Gull (Larus canus) incubating on purpose built nesting platform. These "nestboxes" were originally placed to encourage gulls to nest near dwellings in order to harvest their eggs as food : but...

Roger Powell / Common Gull (Larus canus) incubating on purpose built nesting platform. These nestboxes were originally placed to encourage gulls to nest near dwellings in order to harvest their eggs as food : but th...

Steve Gettle / Eastern Bluebird (Sialia sialis) female at nest box, Huron Meadows Metropark, Michigan

Dietmar Nill / Collared flycatcher (Ficedula albicollis) female at nesting box, Swabia, Germany

David Woodfall / Litle tern (Sternula albifrons) taking off from raised nesting platform (fish box) to prevent flooding by high tides, Northumberland, UK

Fabio Liverani / Lesser kestrel (Falco naumanni) nesting in a window box on a balcony with a woman hanging up washing, Matera, Basilicata, Southern Italy

Fabio Liverani / Lesser kestrel (Falco naumanni) nesting in window box, Matera, Basilicata, Southern Italy

Sebastian Kennerknecht / American Kestrel (Falco sparverius) female peeking out of nest box, Prairie du Chien, Wisconsin

Sebastian Kennerknecht / American Kestrel (Falco sparverius) female emerging from nest box, Prairie du Chien, Wisconsin

Sebastian Kennerknecht / American Kestrel (Falco sparverius) male at nest box, Prairie du Chien, Wisconsin

Sebastian Kennerknecht / American Kestrel (Falco sparverius) female at nest box, Prairie du Chien, Wisconsin

Konrad Wothe / Blue Tit (Cyanistes caeruleus) looking out of nestbox, Germany

Konrad Wothe / Blue Tit (Cyanistes caeruleus) with nesting material, Germany

Scott Leslie / Tree Swallow (Tachycineta bicolor) poking head out of nesting box, Nova Scotia, Canada

Jane Burton / Skewbald Mouse {Mus genus} family in a nest box

ANDREW ANDERSON / Pied flycatcher female (Ficedula hypoleuca) removes dead chick from nest box, UK

Flip de Nooyer / Blue Tit (Cyanistes caeruleus) parent at nest entrance with a caterpillar in its mouth, Europe

Konrad Wothe / Blue Tit (Cyanistes caeruleus) parent delivering worm to chicks in nest box, Europe

Charlie Hamilton James / Kestrel with chicks in London window box, England

Sebastian Kennerknecht / Cassin's Auklet (Ptychoramphus aleuticus) artifical nesting burrows on hillside with Western Gulls (Larus occidentalis), South Farallon Islands, Farallon Islands, Farallon National Wildlife Refuge, Ca...

Luciano Candisani / Hyacinth Macaw (Anodorhynchus hyacinthinus) pair on nest box installed by researcher Neiva Guedes, Pantanal, Brazil

Luciano Candisani / Hyacinth Macaw (Anodorhynchus hyacinthinus) researcher, Cezar Correa, looking for eggs inside nest box, Pantanal, Brazil

Luciano Candisani / Hyacinth Macaw (Anodorhynchus hyacinthinus) researcher with just captured newborn, while other researcher is at nest box, endangered species, Pantanal Ecosystem, Brazil

Luciano Candisani / Hyacinth Macaw (Anodorhynchus hyacinthinus) emerging from nest box, Pantanal Ecosystem, Brazil

Flip de Nooyer / Eurasian Kestrel (Falco tinnunculus) group of five juveniles in nesting box, Europe

Mike Read / Barn owl pole-mounted nesting box {Tyto alba} UK