Andrew Walmsley / Pair of Siamang gibbon (Hylobates / Symphalangus syndactylus) vocalising together, note the male's extended throat pouch, Captive, New Zealand, endangered species

Patrick Morris / Magnificent frigate bird {Fregata magnificens} male displaying with inflated throat pouch, Genovesa Is, Galapagos

DOC WHITE / Blue whale (Balaenoptera musculus) feeding at surface, throat pouch expanded, Pacific

Barry Bland / Brown Pelican {Pelecanus occidentalis} with beak raised, displaying distinctive pouch / gullet, Florida, USA

Bengt Lundberg / Common swift (Apus apus) flying to nestbox, throat pouch full of insects for young, Sweden. July

Steven David Miller / Close up of head and throat pouch of American alligator (Alligator mississippiensis) USA

Hiroya Minakuchi / Blue Whale (Balaenoptera musculus) filter feeding, showing underside of expandable, pleated throat pouch, Sea of Cortez, Gulf of California, Mexico

Hiroya Minakuchi / Blue Whale (Balaenoptera musculus) surfacing, showing underside of expandable, pleated throat pouch, Channel Islands, California

Duncan Usher / Yellow-bellied Toad (Bombina variegata) with inflated throat pouch, Europe

Tui De Roy / Great Frigatebird (Fregata minor) male in courtship display with fully inflated throat pouch, Darwin Bay, Genovesa

DOC WHITE / Blue whale (Balaennoptera musculus) feeding, throat pouch expanded, Monterey, California, USA

Hiroya Minakuchi / Blue Whale (Balaenoptera musculus) filter feeding, extended gular pouch showing throat grooves, endangered, Sea of Cortez, Mexico