Phil Savoie / Yellow legged mining bee (Andrena flavipes) female at nest burrow, River Monnow, Monmouthshire, Wales, UK, April.

Brian Bevan / Pantaloon bee (Dasypoda hurtles) entering burrow with pollen, Bedfordshire, England, UK, August.

Terry Whittaker / Water vole (Arvicola amphibius) swimming underwater, dragging nesting material back to its burrow, Kent, England, UK. October.

Danny Green / Atlantic Puffin (Fratercula arctica) looking down a nesting chamber, Skomer Island, Wales, UK, May

Danny Green / Atlantic Puffin (Fratercula arctica) coming out of its burrow with a gift, Skomer Island, Wales, UK, May

Pete Oxford / Green Iguana (Iguana iguana) female in nest burrow, Banco Chinchorro, Yucatan Peninsula, Mexico

Cyril Ruoso / Atlantic puffin (Fratercula arctica) seen from burrow, Iceland. July.

Dong Lei / Black lipped pika (Ochotona curzoniae ) outside of nest hole, Serxu, Shiqu county, Sichuan Province, Qinghai-Tibet Plateau, China. August 2010.

Tui De Roy / Little blue / fairy penguin (Eudyptula minor) walking on pathway to nesting burrows, Neck Game Reserve, Bruny Island, Tasmania, Australia, December.

Sebastian Kennerknecht / Atlantic Puffin (Fratercula arctica) at nest burrow, Skomer Island National Nature Reserve, Skomer Island, Pembrokeshire, Wales, United Kingdom

Ammonite / Two male Mining bees (Andrena praecox) trying to reach a female bee in a hole, France, March.

Ammonite / Two male Mining bees (Andrena praecox) attacking a third male bee emerging from a hole with orchid pollinia attached, France, March.