Ashley Cooper / Scientific experiment by scientists from Sydney University, Australia, in the Snowy mountains. The study is monitoring C02 exchange between the atmosphere and the soil on a grassland plot. February 20...

Bruno D'Amicis / European Lanner falcon (Falco biarmicus feldeggi) prey exchange between adult male and larger female. Central Apennines, Italy, April.

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

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

Cyril Ruoso / Canada geese (Branta canadensis) in heated exchange, Seine Valley, France, May

Chien Lee / Giant Forest Ant (Camponotus gigas) attending to Leaf-footed Bugs (Notobitus sp), providing protection in exchange for honeydew which is secreted at their abdomen, Danum Valley Conservation Area, Saba...

Chien Lee / Giant Forest Ant (Camponotus gigas) attending to Leaf-footed Bugs (Notobitus sp), providing protection in exchange for honeydew which is secreted at their abdomen, Danum Valley Conservation Area, Saba...

Chien Lee / Giant Forest Ant (Camponotus gigas) attending to Leaf-footed Bug (Notobitus sp), providing protection in exchange for honeydew which is secreted at their abdomen, Danum Valley Conservation Area, Sabah...

Clay Bolt / Carpenter Ants (Camponotus pennsylvanicus) guarding Beech Blight Aphids (Grylloprociphilus imbricator) in exchange for honeydew, which the aphids excrete, Southern Appalachians, South Carolina, USA, O...

Ammonite / Close-up of Honey bees (Apis mellifera) inside hive, showing trophallactic contact, an exchange of between individual workers in order to share information on food quality, France, July.

Frederique Olivier / Inexperienced Emperor penguin (Aptenodytes forsteri) pair going through the motions of egg exchange with a piece of ice, one with ice, the other fighting, Antarctica, May.

Frederique Olivier / Inexperienced Emperor penguin (Aptenodytes forsteri) pair going through the motions of egg exchange with a piece of ice, Antarctica, June.