Nick Upton / European eel (Anguilla anguilla) elver migrating upstream, using an eel pass on the side of a weir, Somerset Levels, England, UK, July.

David Perpinan / Male Mediterranean tree frog (Hyla meridionalis) calling, showing vocal sac inflating, Barcelona, Spain, May. Filmed at night with an infrared camera.

David Perpinan / Common rock sparrow (Petronia petronia) feeding chicks in nest, filmed using an infra-red camera, Cuenca, Castile-La Mancha, Spain, June.

David Perpinan / Common rock sparrow (Petronia petronia) chick exploring outside nest, Cuenca, Castile-La Mancha, Spain, June.

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

Dave Bevan / Red fox (Vulpes vulpes) digging out a mouse nest from under a raised bed, filmed at night using an infra red camera, Carmarthenshire, Wales, UK, January.

Dave Bevan / Juvenile Brown rats (Rattus norvegicus) raiding a chicken nest in a barn, filmed at night using an infra red camera, Carmarthenshire, Wales, UK, December.

Dave Bevan / Juvenile Brown rat (Rattus norvegicus) entering live trap and escaping, filmed at night using an infra red camera, Carmarthenshire, Wales, UK, November.

Dave Bevan / Juvenile Brown rat (Rattus norvegicus) feeding on grain in a barn, filmed at night using infra red, Carmarthenshire, Wales, UK, October.

Dave Bevan / Pair of Swallows (Hirundo rustica) feeding chicks at nest in a barn, filmed using infra red, Carmarthenshire, Wales, UK, September.

Nick Upton / Eurasian beaver (Castor fiber) adding a branch to its dam, Tayside, Scotland, UK, May. Filmed at night using a remote camera and infra red light.

Nick Upton / Two Eurasian beaver kits (Castor fiber) feeding at night, born in the wild on the River Otter as part of the River Otter Beaver Trial, Devon, England, UK, August 2015.