David Perpinan / Female Rock sparrow (Petronia petronia) feeding chick inside nest, filmed with an infrared camera, Spain, June.

Dave Bevan / Slow motion clip of a Blue tit (Cyanistes caeruleus) flying to nest box, enters to feed nestlings and leaves, Carmarthenshire, Wales, UK, June.

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

Ann & Steve Toon / Rock kestrel (Falco rupicolus) at nesting box, Western Cape, South Africa.

Alan Williams / Red mason bee (Osmia bicornis) female sealing entrance to nest hole in bee nesting box. On wall of house, Cheshire, England, UK. May.

Nick Upton / Common swift (Apus apus) flying to a nest box attached to the eaves of a cottage with a feather and straw in its beak to build its nest with, Hilperton, Wiltshire, UK, May 2018.

Nick Upton / Two nest boxes for Common swifts (Apus apus) attached under the eaves of a block of flats, with a nesting Swift peering from one, Edgecombe, Cambridge, UK, July.

Nick Upton / Six nest boxes for Common swifts (Apus apus) in a roof space with swift brick entrance holes and perspex backs so nesting birds can be monitored by a cctv camera and a call playback system, with one n...

Philippe Clement / Great tit (Parus major) bringing food to nestbox to feed chicks, Belgium, April.

Philippe Clement / Great tit (Parus major) bringing food to nestbox to feed chicks, leaves with fecal sac, Belgium, April.

Edwin Giesbers / Wood pigeon (Columba palumbus) nesting in window box of balcony. The Netherlands.

Konrad Wothe / Blue Tit (Cyanistes caeruleus) parent with begging chicks in nest box, Bavaria, Germany

Dave Bevan / Blue tit (Cyanistes caeruleus) flying to nestbox, enters then leaves, Carmarthenshire, Wales, UK, May.

Dave Bevan / Coal tit (Periparus ater) approaching and enterning a nest box, Carmarthenshire, Wales, UK, May.

Dave Bevan / Great tit (Parus major) bringing moss for nest building to nest box, Carmarthenshire, Wales, UK, June.

Dave Bevan / Blue tit (Cyanistes caeruleus) bringing nest building material to a nest box, Carmarthenshire, Wales, UK, March.

Dave Bevan / Blue tit (Cyanistes caeruleus) pecking at the entrance hole in a nest box, Carmarthenshire, Wales, UK, March.

Dave Bevan / Blue tit (Cyanistes caeruleus) pecking at the entrance hole in a nest box, Carmarthenshire, Wales, UK, March.

James Dunbar / Female Leafcutter bee (Megachile willughbiella) arriving at her nest with a cut leaf, Bristol, England, UK, July.

Roger Powell / Common gull (Larus canus) incubating in a nesting tray. These man-made structures were originally erected to ensure a fresh supply of eggs but are now part of a conservation programme.Porsanger fjord,...

Roger Powell / Eurasian oystercatcher (Haematopus ostralegus) standing over eggs in a nesting tray. These nest platforms were originally put up (early - mid 20th century) to provide a supply of fresh eggs. Now they...

Roger Powell / Eurasian oystercatcher (Haematopus ostralegus) incubating in a nesting tray. These nest platforms were originally put up (early - mid 20th century) to provide a supply of fresh eggs. Now they are part...

David Tipling / House sparrow (Passer domesticus) female feeding chick in nestbox at breeding colony Norfolk, UK May

David Tipling / House sparrow (Passer domesticus) pair at nestbox with chick at breeding colony Norfolk, UK May

Ann & Steve Toon / House sparrow (Passer domesticus) male in nest box, Caerlaverock Wildfowl and Wetland Trust reserve, Dumfries and Galloway, Scotland, UK, February

Nick Upton / Mason wasp / Potter wasp (Ancistrocerus sp.) inspecting a nest hole in a drilled log within an insect hotel, Gloucestershire garden, UK, April.

Konrad Wothe / Blue Tit (Cyanistes caeruleus) parent feeding young in nest box, Bavaria, Germany

Konrad Wothe / Blue Tit (Cyanistes caeruleus) parent feeding young in nest box, Bavaria, Germany

Konrad Wothe / Blue Tit (Cyanistes caeruleus) parent collecting fecal sac in nest box, Bavaria, Germany

Michael W. Richards / Blue tit (Cyanistes caeruleus) in flight carrying grass to make nest in nest box, Somerset, UK, April.

Chris Mattison / Common carder bee (Bombus pascuorum) colonising old bird nesting box, UK.

Folkert Christoffers / Eurasian Kestrel (Falco tinnunculus) chicks in nest box, Lower Saxony, Germany

Folkert Christoffers / Eurasian Kestrel (Falco tinnunculus) chicks in nest box, Lower Saxony, Germany

Philippe Clement / Man-made 'insect hotel' offering artificial nesting facilities for solitary bees and cavities for hibernating ladybirds and other insects. Made from reed and bamboo stems, drilled holes in woodblocks,...

Philippe Clement / Man-made 'insect hotel' offering artificial nesting facilities for solitary bees and cavities for hibernating ladybirds and other insects.

Philippe Clement / Man-made 'insect hotel' offering artificial nesting facilities for solitary bees and cavities for hibernating ladybirds and butterflies.

Markus Varesvuo / European Roller (Coracia garrulus) perched on nest box where starlings are nesting, Hungary.

Marie Read / Eastern bluebird (Sialia sialis) pair on nest box roof, female carrying nest material (mainly pine needles) New York, USA, April.

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

Folkert Christoffers / Eurasian Kestrel (Falco tinnunculus) parent and chicks, Lower Saxony, Germany

Glenn Bartley / Mountain Bluebird (Sialia currucoides) female carrying insect prey, Alberta, Canada

Alan Murphy / Eastern Screech Owl (Megascops asio) chicks peering out of nest box, Texas

Philippe Clement / 'Insect hotel' shelter and nesting box for various insects. In blackberry bush (Rubus sp.) in garden, Belgium, June.

Philippe Clement / 'Insect hotel' shelter and nesting box for various insects. In blackberry bush (Rubus sp.) in garden, Belgium, June.

Andy Sands / Female Red mason bee (Osmia bicornis) carrying mud to seal nest cell in an insect box, Hertfordshire, England, UK, May.

Andy Sands / Female Red mason bee (Osmia bicornis) carrying mud to seal nest cell in an insect box, Hertfordshire, England, UK, May.

Andy Sands / Female Red mason bee (Osmia bicornis) carrying mud to seal nest cell in an insect box, Hertfordshire, England, UK, May.

Andy Sands / Female Red mason bee (Osmia bicornis) carrying mud to seal nest cell in an insect box, Hertfordshire, England, UK, May.

Andy Sands / Female Red mason bee (Osmia bicornis) carrying mud to seal nest cell in an insect box, Hertfordshire, England, UK, May.

Andy Sands / Female Blue mason bee (Osmia caerulescens) carrying pollen on its abdominal scopa (pollen carrying hairs) to a nest cell in an insect box, Hertfordshire, England, June.

Andy Sands / Female Blue mason bee (Osmia caerulescens) flying into an insect box, with mandibles covered in pollen, Hertfordshire, England, June.

Andy Sands / Female Blue mason bee (Osmia caerulescens) covered in pollen flying into an insect box in a garden, carrying bits of wood to seal nest cells, Hertfordshire, England, June.

Andy Sands / Female Blue mason bee (Osmia caerulescens) flying into an insect box in a garden carrying leaf mastic (masticated leaf sections) to seal nest cells, Hertfordshire, England, June.

Andy Sands / Female Blue mason bee (Osmia caerulescens) flying into an insect box in a garden carrying leaf mastic (masticated leaf sections) to seal nest cells, Hertfordshire, England, June.

D. Parer & E. Parer-Cook / Little Blue Penguin (Eudyptula minor) being examined by scientist, Phillip Island, Australia

D. Parer & E. Parer-Cook / Little Blue Penguin (Eudyptula minor) adult with down-covered chick in nesting box, Phillip Island, Australia

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