Mark Carwardine / Aerial view of Fin whale (Balaenoptera physalus) lunge-feeding, with throat pouch distended, southern Sea of Cortez (Gulf of California), Baja California, Mexico.

Mark Carwardine / Aerial view of Fin whale (Balaenoptera physalus) lunge-feeding, with mouth open and throat pouch distended, southern Sea of Cortez (Gulf of California), Baja California, Mexico.

Ole Jorgen Liodden / Magnificent frigatebird (Fregata magnificens) male with gular pouch, Galapagos.

Ole Jorgen Liodden / Brown pelican (Pelecanus occidentalis urinator) close up of throat pouch skin, with beak open, Galapagos.

Ole Jorgen Liodden / Magnificent Frigatebird (Fregata magnificens) male displaying, red throat pouch inflated. Galapagos

Patrick Morris / Magnificent frigate bird {Frigata magnificens} pair on nest, male displaying with red throat pouch inflated, Genovesa Is, Galapagos

PREMAPHOTOS / Aquatic anole male lizard displaying, rainforest, Costa Rica

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

John Chan / California brown pelicans (Pelecanus occidentalis californicus) stretching their gular pouches and preening, resting near to a flock of Elegant terns (Thalasseus elegans), Southern California, USA, Ma...

Mark Carwardine / Aerial view Fin whales (Balaenoptera physalus) lunge-feeding with throat pouch distended, southern Sea of Cortez (Gulf of California), Baja California, Mexico.

Sandesh Kadur / Magnificent frigatebird (Fregata magnificens) resting on the ground with red throat pouch inflated, Galapagos Islands, Ecuador.

Lynn M. Stone / Magnificent frigate bird (Fregata magnificens) perched in Red mangrove (Rhizophora mangle) tree. Tampa Bay islet roosts, Tierra Verde, Pinellas County, Florida, USA.