Ingo Arndt / Tiger beetle pupates in underground burrow {Cicindela hybrida} Germany

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

Adrian Davies / Blackback land crab (Gecarcinus lateralis) dragging leaf into burrow, Barbados.

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.

Konstantin Mikhailov / Mongolian five-toed jerboa (Allactaga sibirica) digging burrow, Gobi, Mongolia, August.

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

Donald M. Jones / Burrowing Owl (Athene cunicularia) owlets at burrow with one stretching, Montana

Donald M. Jones / Burrowing Owl (Athene cunicularia) parent and owlet at burrow, Montana

Tui De Roy / Little blue / fairy penguin (Eudyptula minor) pair courting near nesting burrow, Neck Game Reserve, Bruny Island, Tasmania, Australia, December.

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