Paul Bertner / Spiny Ant (Polyrhachis sp) pair exchanging food, Danum Valley Conservation Area, Sabah, Borneo, Malaysia

Dave Bevan / Pair of Wood pigeons (Columba palumbus) perched in a Hawthorn tree (Crataegus monogyna), exchanging food, Gloucestershire, England, UK, June.

Frederique Olivier / Wide angle view of a pair of Royal penguins (Eudyptes schlegeli) exchanging an egg in a colony, Macquarie Island, Australian Antarctica.

Mark Taylor / Collie cross dogs Brec and Bliss, exchanging angry snarls. Brec with hackles raised.

Ingo Arndt / Whiskered Tern (Chlidonias hybrida) male passing mayfly to female during courtship, Danube Delta, Romania

Thomas Hinsche / Common Kingfisher (Alcedo atthis) pair exchanging fish during courtship, Saxony-Anhalt, Germany

John Cancalosi / Leopard slug (Limax maximus) pair mating, white male organs exchanging sperm, hermaphroditic species, New York, USA, August.

David Pattyn / Great Crested grebes (Podiceps cristatus) performing courtship dance and exchanging weed as part of ritual, La Dombes area, France, June

Simon Colmer / Honey bee (Apis mellifera) workers exchanging food - known as trophallaxis, Sussex, UK

Donald M. Jones / Limpkin (Aramus guarauna) pair exchanging snail, central Florida

Tui De Roy / Rockhopper Penguin (Eudyptes chrysocome) pair exchanging incubation duties, New Island, Falkland Islands

Heike Odermatt / Northern Gannet (Morus bassanus) pair exchanging nest material mid-flight, Helgoland, Germany