Thomas Marent / Bonobo (Pan paniscus) hooting, Lola Ya Bonobo Sanctuary, Democratic Republic of the Congo

Florian Möllers / Female Chimpanzee (Pan troglodytes schweinfurthii) "Kalema" with her baby "Klauce", calling, hooting. Budongo Forest Reserve, Masindi, Uganda, Africa. December

Fiona Rogers / Eastern Chimpanzee (Pan troglodytes schweinfurthii) seventeen year old male, named Fudge, hooting, Gombe National Park, Tanzania

Gerrit Vyn / Great Horned Owl (Bubo virginianus) adult female hooting, Sublette County, Wyoming, USA, May

Fiona Rogers / Eastern Chimpanzee (Pan troglodytes schweinfurthii) eighteen year old male hooting, Gombe National Park, Tanzania

Anup Shah / Eastern Chimpanzee (Pan troglodytes schweinfurthii) baby male, one year old, hooting, Gombe National Park, Tanzania

Anup Shah / Eastern Chimpanzee (Pan troglodytes schweinfurthii) fourteen year old female with her nine month old baby daughter calling, Gombe National Park, Tanzania

Thomas Marent / Bonobo (Pan paniscus) hooting, Sanctuary, Democratic Republic of the Congo

Thomas Marent / Chimpanzee (Pan troglodytes) hooting, Lekedi Natural Preserve, Gabon

Anup Shah / Eastern Chimpanzee (Pan troglodytes schweinfurthii) female, forty years old, calling while holding her two month old granddaughter, Gombe National Park, Tanzania

Anup Shah / Eastern Chimpanzee (Pan troglodytes schweinfurthii) juvenile male, eleven years old, displaying in tree, Gombe National Park, Tanzania

Fiona Rogers / Eastern Chimpanzee (Pan troglodytes schweinfurthii) mother holding two month old baby, Gombe National Park, Tanzania