Eric Baccega / Siamang Gibbon (Hylobates syndactylus) vocalising, vocal pouch inflated, captive, native to forests of Malaysia, Sumatra and Thailand

John Cancalosi / Colorado river toad (Incilius alvarius) male calling to attract females, vocal sac filled with air. Sonoran desert, Arizona, USA. August.

Roy Mangersnes / Magnificent frigatebird (Fregata magnificens) male displaying, red throat pouch inflated, North Seymour Island, Galapagos.

Roy Mangersnes / Magnificent frigatebird (Fregata magnificens) male displaying, red throat pouch inflated, North Seymour Island, Galapagos.

Roy Mangersnes / Magnificent frigatebird (Fregata magnificens) male displaying, red throat pouch inflated, North Seymour Island, Galapagos.

Roy Mangersnes / Magnificent frigatebird (Fregata magnificens) male displaying with red throat pouch inflated, Genovesa Island, Galapagos.

Cyril Ruoso / Common tree frog (Hyla arborea) male calling at night with inflated vocal pouch. Burgundy, France, April.

Konrad Wothe / Brilliant thighed poison frog (Allobates femoralis) calling, with vocal pouch inflated. Panguana Reserve, Huanuco province, Amazon basin, Peru.

Pete Oxford / Magnificent frigatebird (Fregata magnificens) male with pouch inflated. Galapagos.

Ross Hoddinott / Great frigatebird (Fregata minor) male with vocal pouch inflated, Genovesa Island, Galapagos, Ecuador. May.

Bert Willaert / Male brown/green morph of Darwin's Frog (Rhinoderma darwinii) on leaf with juveniles in vocal pouch, Chile, January, Vulnerable species

Bert Willaert / Male green Darwin's Frog (Rhinoderma darwinii) with young in vocal pouch, Chile, December 2012, Vulnerable species