Martin Willis / Budgerigar (Melopsittacus undulatus) father with begging chick at nest cavity, Queensland, Australia

John Shaw / Western screech owl (Megascops kennicottii) is camouflaged as it looks from a tree cavity. Bosque del Apache National Wildlife Refuge, New Mexico, USA, January.

Chien Lee / Minden / White-footed Sportive Lemur (Lepilemur leucopus) in cavity, Madagascar

Cyril Ruoso / Chimpanzee (Pan troglodytes) using stick to forage for prey in small tree cavity, Bossou, Guinea

Cyril Ruoso / Chimpanzee (Pan troglodytes) using stick to forage for prey in small tree cavity, Bossou, Guinea

Murray Cooper / Spot-breasted Woodpecker (Colaptes punctigula) at nest cavity, South America

Doug Wechsler / Yellow-plumed parakeets (Leptosittaca branickii) at nest cavity in wax palm stump, Tapichalaca Biological Reserve, Ecuador.

Michael Quinton / Northern Flicker (Colaptes auratus) carrying fecal sac from nest cavity in forest, Alaska

Michael Quinton / American Marten (Martes americana) emerging from tree cavity, Alaska

Michael Quinton / American Marten (Martes americana) sleeping in tree cavity, Alaska

Donald M. Jones / Red-breasted Nuthatch (Sitta canadensis) chick in nest cavity, western Montana

Alan Murphy / Northern Flicker (Colaptes auratus) female at nest cavity with chicks, British Columbia, Canada