Robin Chittenden / Common swift (Apus apus) flying low to water while hunting, Norfolk, England, UK, July. Winner of Animal Behaviour Category of the British Wildlife Photography Awards 2019.

Dave Bevan / Slow motion clip of a pair of Common swifts (Apus apus) approaching and entering a nest hole in limestone cliff, Norfolk, England, UK, May.

Nick Upton / Common swifts (Apus apus) flying overhead, Wiltshire, UK, June. Digital composite image.

Phil Savoie / Swift (Apus apus) flock screaming in flight against blue sky and clouds, Monmouthshire Wales, UK, July.

Phil Savoie / Swift (Apus apus) flock screaming in flight against blue sky and clouds, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) flock screaming in flight against blue sky and clouds, Monmouthshire, Wales, UK, July.

Nick Upton / Common swift (Apus apus) feeding chick in a nest box, filmed using infrared light, Cambridge, England, UK, August.

Markus Varesvuo / Swift (Apus apus) in flight. Helsinki, Finland. July

Markus Varesvuo / Common Swift (Apus apus) in flight, Helsinki Finland July

Kim Taylor / Common swift {Apus apus} nestling. Captive, UK

Ann & Steve Toon / Merlin (Falco columbarius) with Swift (Apus apus) prey , Cumbria, UK, captive. July

Phil Savoie / Swift (Apus apus) in flight with blue cloudy sky, Monmouthshire, Wales, UK. April

Phil Savoie / Swift (Apus apus) in flight with blue cloudy sky, Monmouthshire, Wales, UK. July

Nick Upton / Common swift (Apus apus) flying overhead, Lacock, Wiltshire, UK, June.

Robin Chittenden / Common Swift (Apus apus) in flight reflected in water, Norfolk, England, UK. July.

Robin Chittenden / Common Swift (Apus apus) in flight reflected in water, Norfolk, England, UK. July.

Robin Chittenden / Common swift (Apus apus) hunting over water, Norfolk, England, UK, July.

Robin Chittenden / Common swift (Apus apus) hunting over water, Norfolk, England, UK, July.

Robin Chittenden / Common swift (Apus apus) hunting over water, Norfolk, England, UK, July.

Robin Chittenden / Common swift (Apus apus) Norfolk, England, UK. July.

Dave Bevan / Slow motion clip of a Common swift (Apus apus) flying and landing on a rockface before entering nest crevice, Norfolk, England, UK, July.

Dave Bevan / Slow motion clip of a Common swift (Apus apus) flying from nest crevice in a rock face Norfolk, England, UK, July.

Nick Upton / Nick Upton setting up a remote camera on an extension roof to photograph Common swifts (Apus apus) coming and going from a nest box under the eaves of a cottage, Hilperton, Wiltshire, UK, June 2016. M...

Nick Upton / Common swift (Apus apus) flying overhead, having just arrived after migration from African wintering grounds, Lacock, Wiltshire, UK, May.

Nick Upton / Common swifts (Apus apus) flying over rooftops, having just arrived after migration from African wintering grounds, Lacock, Wiltshire, UK, May.

Martin Grimm/ BIA / Common Swift (Apus apus) flying, Baden-Wurttemberg, Germany

Nick Upton / People watching Swifts (Apus apus) flying around an old cottage they are nesting in during a swift walk organised by the local swift group, Bradford-on-Avon, Wiltshire, UK, June. Model released.

Nick Upton / Four orphaned Common swift chicks (Apus apus), almost grown to full size, held in a keeping cage and about to be fed by Judith Wakelam, Worlington, Suffolk, UK, July.

Nick Upton / Two orphaned Common swift chicks (Apus apus), almost grown to full size, held in a keeping cage and about to be fed by Judith Wakelam, Worlington, Suffolk, UK, July.

Nick Upton / People watching Swifts (Apus apus) flying around Holy Trinity church during a swift walk organised by the local swift group, Bradford-on-Avon, Wiltshire, UK, June. Digital composite. Model released.

Nick Upton / Common swift (Apus apus) flying to its nest in a Swift nest box in the belfry of All Saints Church, Worlington, Suffolk, UK, July.

Nick Upton / Common swift (Apus apus) flying from a nest box after feeding its chicks, Hilperton, Wiltshire, UK, 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 / Two Common swift eggs (Apus apus) in a nest box in a church belfry, inspected during a ringing study, Worlington, Suffolk, UK, July.

Nick Upton / Two compartment nest box for Common swifts (Apus apus) attached under the eaves of a house, Landbeach, Cambridgeshire, UK, July.

Nick Upton / Common swift chick (Apus apus) reared to full size by Judith Wakelam, climbing up the side of a child's play pen and almost ready to be released, Worlington, Suffolk, UK, July.

Nick Upton / Judith Wakelam returns an orphan Common swift chick (Apus apus) to a child's play pen used to house several chicks after feeding it, Worlington, Suffolk, UK, July. Model released.

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 / All Saints Church which has over 40 swift nestboxes in the belfry and a thriving colony of breeding Common swifts (Apus apus), Worlington, Suffolk, UK, July.

Nick Upton / Common swift (Apus apus) two flying over the weathercock on the spire of Holy Trinity Church, Bradford-on-Avon, Wiltshire, UK, June.

Nick Upton / Screaming party of Common swifts (Apus apus) flying around a church bell tower at dusk, where a large colony breeds in nestboxes behind the window louvres, All Saints Church, Worlington, Suffolk, UK,...

Nick Upton / Screaming party of Common swifts (Apus apus) flying around a church bell tower at dusk, where a large colony breeds in nestboxes behind the window louvres, All Saints Church, Worlington, Suffolk, UK,...

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

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

Nick Upton / Five nestboxes 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 / Five nest boxes for Common swifts (Apus apus) attached under the eaves of a house, Milton, Cambridge, UK, July.

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 / 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 / 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...

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

Nick Upton / Two multiple nestboxes for Common swifts (Apus apus) attached to the wall of a block of flats, Edgecombe, Cambridge, UK, July.

Nick Upton / Swift lousefly (Craeterina pallida), a blood sucking parasite unique to swift nests, found on a Swift chick (Apus apus) and held in the hands of a bird ringer, Worlington, Suffolk, UK, July. Model rel...

Nick Upton / Common swift (Apus apus) flying back to its nest under the roof of an old half-timbered house with several swift nests under it, Lacock, Wiltshire, UK, June.

Nick Upton / Common swift (Apus apus) flying overhead, Lacock, Wiltshire, UK, May.

Nick Upton / Common swift (Apus apus) flying to a nest box with its throat pouch bulging with insects it has caught to feed its chicks, Hilperton, Wiltshire, UK, June.

Nick Upton / Two recently hatched Common swift chicks (Apus apus) in a nest box in a church belfry, inspected during a ringing study, Worlington, Suffolk, UK, July.

Nick Upton / Two recently hatched Common swift chicks (Apus apus) in a nest box in a church belfry, inspected during a ringing study, Worlington, Suffolk, UK, July.

Nick Upton / Young Common swift chick (Apus apus) removed briefly from a nest box being ringed by Simon Evans in a church belfry, Worlington, Suffolk, UK, July. Model released.

Nick Upton / Common swift (Apus apus) two flying past the weathercock on the spire of Holy Trinity Church, Bradford-on-Avon, Wiltshire, UK, June.

Roger Powell / Common swift (Apus apus) in flight. Druridge Bay, Northumberland, England, UK. July.

Phil Savoie / Swift (Apus apus) flying against blue sky, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) in flight calling to chicks in nest under house eaves, Monmouthshire, Wales, UK, July.

Phil Savoie / Swifts (Apus apus) in flight above Chepstow Castle, Monmouthshire, Wales, UK, July.

Phil Savoie / Swifts (Apus apus) flying, screaming to chicks in nest under eaves of house, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) defecating in flight, Monmouthshire, Wales, UK, June.

Phil Savoie / Swift (Apus apus) flock in flight, Monmouthshire, Wales, UK, June.

Phil Savoie / Swift (Apus apus) in flight, Monmouthshire, Wales, UK, June.

Phil Savoie / Swift (Apus apus) in flight, Monmouthshire, Wales, UK, June.

Phil Savoie / Swift (Apus apus) in flight, Monmouthshire, Wales, UK, June.

Phil Savoie / Swift (Apus apus) in flight at dusk, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) in flight with bulging mouthful of insects for young, Monmouthshire, Wales, UK, June.

Phil Savoie / Swift (Apus apus), with bulging mouthful of insects for young, Monmouthshire, Wales, UK, June.

Phil Savoie / Swift (Apus apus) in flight, Monmouthshire Wales UK, July.

Phil Savoie / Swift (Apus apus) carrying feather for nest Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) in flight, Monmouthshire, Wales, UK, October.

Phil Savoie / Swift (Apus apus) in flight, Monmouthshire, Wales, UK, June.

Phil Savoie / Swift (Apus apus) in flight with mouth full of insect prey to feed to chicks, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) in flight, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) flock in flight against blue sky and clouds, screaming behaviour, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) flock in flight against blue sky and clouds, screaming behaviour, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) in flight with mouth full of insect prey to feed to chicks, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) in flight with mouth full of insect prey to feed to chicks, Monmouthshire, Wales, UK, July.

Phil Savoie / Swift (Apus apus) flock in flight, screaming behaviour, Monmouthshire, Wales, UK, July.

David Williams/ BIA / Common Swift (Apus apus) flying, Wales, United Kingdom

Nick Upton / Common swift chick (Apus apus) almost fully grown resting in the nest cup as a parent prepares to leave a nest box after feeding the chick, Cambridge, UK, August.

Nick Upton / Common swift chick (Apus apus) almost fully grown sitting in a nest cup calling loudly to beg for food from a parent that has just returned to its nest box from a foraging trip with a throat pouch ful...

Nick Upton / Common swift chick (Apus apus) almost fully grown stretching its wings and flapping them as it sits on the nest cup in a nest box a few days before fledging, Cambridge, UK, August.

Nick Upton / Common swift chick (Apus apus) almost fully grown preening as it rests on the nest cup in a nest box, Cambridge, UK, August.

Nick Upton / Common swift chick (Apus apus) almost fully grown scratching its head with a foot as it rests on the nest cup in a nest box, Cambridge, UK, August.

Nick Upton / Common swift chick (Apus apus) almost fully grown preening its wing as it rests on the nest cup in a nest box, Cambridge, UK, August.

Nick Upton / Common swift chick (Apus apus) almost fully grown resting in a nest box in an attic, one of several monitored by an infrared CCTV system, Cambridge, UK, August.

Nick Upton / Simon Evans taking a Common swift chick (Apus apus) from a nest box in All Saints Church belfry briefly to ring it, Worlington, Suffolk, UK, July. Model released.

Nick Upton / Common swift (Apus apus) pair resting in their nest box alongside their chick, Cambridge, UK, July.