Roland Seitre / Blue throated / Wagler's macaw (Ara glaucogularis) chick in nestbox, Santa Cruz Zoo, Teneriffe, Canary Islands, Critically endangered species from Bolivia

Chris Gomersall / 2020VISION / Common starling (Sturnus vulgaris) adult with insect food arriving at nestbox to feed chicks, Hope Farm RSPB Reserve, Cambridgeshire, England, UK, May

Wild Wonders of Europe / Cairns / Tengmalm's owl (Aegolius funereus) peering out of nestbox, Bergslagen, Sweden, June 2009

Wild Wonders of Europe / Varesvuo / European Roller (Coracias garrulus) pair with intruder Roller in nestbox, Hungary May 2008

Wild Wonders of Europe / Varesvuo / European Roller (Coracias garrulus) attacking intruder Roller in nestbox, Pusztaszer, Hungary, May 2008

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

Wild Wonders of Europe / Varesvuo / Red-footed Falcon (Falco vespertinus) male brings vole prey to female in nestbox, Hortobagy NP, Hungary, May 2008

Wild Wonders of Europe / Varesvuo / European Roller (Coracias garrulus) pulling intruder Roller out of nestbox, Pusztaszer, Hungary, May 2008

Colin Varndell / Blue tit brings caterpillar to young in nestbox {Parus caeruleus} UK

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

Rolf Nussbaumer / Fat dormouse in bird nestbox {Glis glis} Switzerland.

Bengt Lundberg / Kitten sitting on nestbox of Great tit, Sweden

Bengt Lundberg / Great tit brings food to nine hungry week-old chicks in nestbox, Sweden {Parus major} Sweden

Konrad Wothe / Starling (Sturnus vulgaris) at nestbox in garden, Bavaria, Germany . April

Konrad Wothe / Blue tit (Cyanistes caeruleus) feeding young in the nestbox, Bavaria, Germany, May.

Konrad Wothe / Blue tit (Cyanistes caeruleus) feeding young in the nestbox, Bavaria, Germany, May.

Roger Powell / Old Goldeneye Nestbox crafted from a log and chained to the side of a lodge to protect it from Wolverines. Kaalimaa, Pokka, Inari, Lapland, Finland

Roger Powell / Old Goldeneye Nestbox crafted from a log and chained to the side of a lodge to protect it from Wolverines. Kaalimaa, Pokka, Inari, Lapland, Finland, June.

Nick Upton / Monitor linked to an infra red camera in a Common swift (Apus apus) nestbox with an adult sitting beside two well developed chicks in a nest cup, Worlington, UK, Suffolk.

Nick Upton / House sparrow (Passer domesticus) using a nestbox intended for Common swifts (Apus apus) made from plastic piping, attached to the wall of a block of flats, Edgecombe, Cambridge, UK, July.

Nick Upton / Nestbox for Common swifts (Apus apus) made from plastic piping, attached to the wall of a block of flats, Edgecombe, Cambridge, UK, July.

Nick Upton / Roger Beckett building a nestbox for Common swifts (Apus apus) with nest cups, access ports for nest inspection and CCTV cameras, to be fitted in a church tower, Hilperton, Wiltshire, UK, June. Model...

Nick Upton / Nestbox being built for Common swifts (Apus apus) with nest cups, access ports for nest inspection and CCTV cameras, to be fitted in a church tower, Hilperton, Wiltshire, UK, June. Model released.

Nick Upton / Roger Beckett building a nestbox for Common swifts (Apus apus) with nest cups, access ports for nest inspection and CCTV cameras, to be fitted in a church tower, Hilperton, Wiltshire, UK, June. Model...

Nick Upton / Swift nestbox on a house wall alongside hollow "swift brick" entrances to nest boxes in a roof space, Worlington, Suffolk, UK, July.

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.

Philippe Clement / Dead Great tit (Parus major) chicks in nestbox starved to death after parents abandoned nest, UK, May

Nick Upton / Common swift (Apus apus) with a throat pouch bulging with insects flying to a swift nestbox attached to the eaves of a cottage to feed its chicks, near Trowbridge, Wiltshire, UK, June.

Dave Bevan / Male Great spotted woodpecker (Dendrocopos major) trying to break into nestbox to predate chicks, Carmarthenshire, Wales, UK, June.

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 / Blue tit (Cyanistes caeruleus) entering and leaving nestbox, Carmarthenshire, Wales, UK, June.

Dave Bevan / Grey squirrel (Sciurus carolinensis) entering a nestbox, Carmarthenshire, Wales, UK, November.

Nick Upton / Spotted flycatcher (Muscicapa striata) feeding a chick which has just left its nestbox with a solitary bee, Cornwall, UK, August.

Nick Upton / Spotted flycatcher (Muscicapa striata) feeding a solitary bee to its chick which has just left the nestbox, Cornwall, UK, August.

David Tipling / House sparrow (Passer domesticus) pair mating on top of nestbox at breeding colony, Norfolk, UK May

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

Laurent Geslin / Tengmalm's / Boreal owl (Aegolius funereus) chick in nestbox with mice prey, during bird ringing Jura, Switzerland. April.

Nick Upton / Barn owl (Tyto alba) nestbox in an Oak tree, Wiltshire, UK, June.

Nick Upton / Little owl chick (Athene noctua) with a well developed wing held open to check primary feather development after ringing during a nestbox survey, Wiltshire, UK, June.

Nick Upton / Little owl chick (Athene noctua) inside a nestbox checked during a survey, Wiltshire, UK, June.

Nick Upton / Little owl chick (Athene noctua) held after being ringed during a nestbox survey, Wiltshire, UK, June.

Nick Upton / Graham Guest at the top of a ladder checking a nestbox for Kestrel chicks (Falco tinnunculus) during a survey for the Hawk and Owl Trust's Kestrel Highways project, Congresbury, Somerset, UK, June. Mo...

Nick Upton / Adult Kestrel (Falco tinnunculus) found in a nestbox during a survey, Wiltshire, UK, June.

Nick Upton / Kestrel chick (Falco tinnunculus) having its developing primary feathers measured during a nestbox survey for the Hawk and Owl Trust's Kestrel Highways project, Congresbury, Somerset, UK, June. Model...

Nick Upton / Colin Morris weighing a Kestrel chick( Falco tinnunculus) in a bag during a nestbox survey for the the Hawk and Owl Trust's Kestrel Highways project, Congresbury, Somerset, UK, June. Model released.

Nick Upton / Four Kestrel chicks (Falco tinnunculus) in a nestbox, one with a mouse in its beak, found during a survey for the Hawk and Owl Trust's Kestrel Highways project, Congresbury, Somerset, UK, June.

Nick Upton / Colon Morris ringing a Kestrel chick (Falco tinnunculus) found during a nestbox survey for the the Hawk and Owl Trust's Kestrel Highways project, Congresbury, Somerset, UK, June. Model released.

Nick Upton / Kestrel chick (Falco tinnunculus) being ringed after being found during a nestbox survey for the the Hawk and Owl Trust's Kestrel Highways project, Congresbury, Somerset, UK, June. Model released.

Nick Upton / Kestrel chick (Falco tinnunculus) being ringed after being found during a nestbox survey for the the Hawk and Owl Trust's Kestrel Highways project, Congresbury, Somerset, UK, June. Model released.

Nick Upton / Graham Guest at the top of a ladder held by Barry Gray putting a Kestrel chick (Falco tinnunculus) back into a nestbox during a survey for the Hawk and Owl Trust's Kestrel Highways project, Congresbur...

Nick Upton / Graham Guest at the top of a ladder removing a Kestrel chick (Falco tinnunculus) from a nestbox for ringing and measuring during a survey for the Hawk and Owl Trust's Kestrel Highways project, Congres...

Nick Upton / Colin Morris takes a Kestrel chick (Falco tinnunculus) for ringing from a bag held by Keith Lapham as Barry Gray and Graham Guest look on during a nestbox survey for the the Hawk and Owl Trust's Kest...

Nick Upton / Kestrel chick (Falco tinnunculus) held after being ringed during a nestbox survey for the the Hawk and Owl Trust's Kestrel Highways project, Congresbury, Somerset, UK, June. Model released.

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

Stephen Dalton / Barn owl (Tyto alba) resting on post near nestbox, Sussex, England, UK. June.

Nick Upton / Dani Rozycka inspecting Edible / Fat Dormouse (Glis glis) nestbox temporarily detached from a Beech treetrunk in woodland where this European species has become naturalised, Buckinghamshire, UK, Augus...

Nick Upton / Edible / Fat Dormouse (Glis glis) peering out of a nestbox attached to a Beech treetrunk in woodland where this European species has become naturalised, Buckinghamshire, UK, August.

Nick Upton / Adult Edible / Fat Dormouse (Glis glis) held temporarily inside a plastic sack it has been tipped into from a nestbox, during a monitoring project in woodland where this European species has become na...

Nick Upton / Edible / Fat Dormouse (Glis glis) peering out of a nestbox attached to a Beech treetrunk in woodland where this European species has become naturalised, Buckinghamshire, UK, August.

Nick Upton / Edible / Fat Dormouse (Glis glis) peering out of a nestbox attached to a Beech treetrunk in woodland where this European species has become naturalised, Buckinghamshire, UK, August.

Nick Upton / Adult female Edible / Fat Dormouse (Glis glis) and her litter of youngsters tipped into a plastic sack from their nestbox during a monitoring project in woodland where this European species has become...

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

Markus Varesvuo / Pied Flycatcher (Ficedula hypoleuca) male looking out from nest box entrance hole, Vaala, Finland, Scandinavia, June.

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

Nick Upton / Ian Chambers and Gill Brown of Backwell Environment Trust returning a torpid Common / Hazel dormouse (Muscardinus avellanarius) to its nestbox after weighing it during a survey in coppiced woodland ne...

Nick Upton / Ian Chambers of Backwell Enviroment Trust lowering a nestbox containing a Common / Hazel dormouse (Muscardinus avellanarius) into a plastic sack held by Gill Brown, before taking measurements, in copp...

Nick Upton / Torpid Common / Hazel dormouse (Muscardinus avellanarius) found sleeping in a Dormouse nestbox set out by Backwell Enviroment Trust in coppiced woodland near Bristol, Somerset, UK, June.

Nick Upton / Torpid Common / Hazel dormouse (Muscardinus avellanarius) sleeping in a Dormouse nestbox set out by Backwell Enviroment Trust in coppiced woodland near Bristol, Somerset, UK, June. Winner of the Docum...

Nick Upton / Adult Common / Hazel dormouse (Muscardinus avellanarius) captured during a survey by Backwell Enviroment Trust in coppiced woodland near Bristol, being encouraged to emerge from a nestbox placed tempo...

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

Ann & Steve Toon / House sparrow (Passer domesticus) male feeding chick at nestbox, Northumberland, UK, August

Charlie Summers / Tree swallow (Tachycineta bicolor) adult feeding aggressive chick that clamps its beak around the adults head, Aurora, Colorado, USA July

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

Roland Seitre / Forest in the Orejiamarillo reserve and palm with parrot nestbox attached. National Park, Jardin, Antioquia, Colombia.

Roland Seitre / Blue throated / Wagler's macaw (Ara glaucogularis) pair at nestbox, Santa Cruz Zoo, Teneriffe, Canary Islands, Critically endangered species from Bolivia

Roland Seitre / Blue throated / Wagler's macaw (Ara glaucogularis) pair at nestbox, Santa Cruz Zoo, Teneriffe, Canary Islands, Critically endangered species from Bolivia

Roland Seitre / Three chicks of Blue throated / Wagler's macaw (Ara glaucogularis) in nestbox put up by conservation team, Trinidad, Beni, Bolivia, Critically endangered species, January 2008, exceptional breeding of...

Roland Seitre / Three chicks of Blue throated / Wagler's macaw (Ara glaucogularis) in nestbox put up by conservation team, Trinidad, Beni, Bolivia, Critically endangered species, January 2008, exceptional breeding of...

Roland Seitre / Chick of Blue throated / Wagler's macaw (Ara glaucogularis) in nestbox put up by conservation team, Trinidad, Beni, Bolivia, Critically endangered species, January 2008

Roland Seitre / Blue throated / Wagler's macaw (Ara glaucogularis) at nestbox put up by conservation team, Trinidad, Beni, Bolivia, Critically endangered species, January 2008

Roland Seitre / Conservation officer, Hernan Vargas Ayala, examines growing chick from nestbox of Blue throated / Wagler's macaw (Ara glaucogularis) and shows it to group of children, Trinidad, Beni, Bolivia, Critica...

Roland Seitre / Ggrowing chicks from nestbox of Blue throated / Wagler's macaw (Ara glaucogularis) Trinidad, Beni, Bolivia, Critically endangered species, January 2008.

Roland Seitre / Conservation officer, Hernan Vargas Ayala, examines growing chick from nestbox of Blue throated / Wagler's macaw (Ara glaucogularis) Trinidad, Beni, Bolivia, Critically endangered species, January 200...

Roland Seitre / Conservation officer, Hernan Vargas Ayala, examining chick from nestbox of Blue throated / Wagler's macaw (Ara glaucogularis) Trinidad, Beni, Bolivia, Critically endangered species, January 2008.

Roland Seitre / Conservation officer, Hernan Vargas Ayala, examining chick from nestbox of Blue throated / Wagler's macaw (Ara glaucogularis) Trinidad, Beni, Bolivia, Critically endangered species, January 2008.

Roland Seitre / Conservation officers putting up nestbox for Blue throated / Wagler's macaw (Ara glaucogularis) Trinidad, Beni, Bolivia, Critically endangered species, January 2008. Nestbox painted with initials of t...