Karine Aigner / Cuban bare-legged owl (Margarobyas lawrencii) in nest hole. Cienaga de Zapata, Cuba.

Steven David Miller / Red-collared lorikeet (Trichoglossus rubritorquis) pair examining hole in Eucalyptus as a potential nesting hollow. Katherine, Northern Territory, Australia.

Bence Mate / European roller (Coracias garrulus) peering out of nest with feather, Lake Csaj, Pusztaszer, Kiskunsagi National Park, Hungary, February.

Claudio Contreras / Morelet's crocodile (Crocodylus moreletii) in sinkhole, Cenote Carwash, near Tulum, Yucatan Peninsula, Mexico, January

Richard Robinson / Blue shark (Prionace glauca) just below surface, Hauraki Gulf, Auckland, New Zealand, June.

Sven Zacek / View through glacier ice towards snow-covered mountains in Kongsfjorden fjord in Svalbard, Norway. June 2015.

Anup Shah / African elephants (Loxodonta africana) gathering at a waterhole, wide angle view. Maasai Mara National Reserve, Kenya.

Franco Banfi / California sea lion (Zalophus californianus), Los Islotes, Sea of Cortez, Baja California peninsula, Mexico, East Pacific Ocean.

Olga Kamenskaya / Young Baikal seal (Pusa sibirica) at breathing hole. Lake Baikal, Russia, April.

Jack Dykinga / Cenote Noh-Moson, is ringed with ficus trees with ten meter long roots reaching toward the blue water below, state of Yucatan, Mexico

Bryan and Cherry Alexander / Meltwater pouring off iceberg above hole. Scoresbysund Fiord, East Greenland, September 2005.

Chris Shields / Illustration of wildlife at African waterhole: Water buffalo (Syncerus caffer),gazelle,African lion (Panthera leo),African elephant (Loxodonta sp), weaver birds (Ploceidae).