Gular skin (throat skin), in ornithology, is an area of featherless skin on birds that joins the lower mandible of the beak (or bill) to the bird's neck.[1]
Gular skin can be very prominent, for example in members of the order Phalacrocoraciformes as well as in pelicans (which likely share a common ancestor). In many species, the gular skin forms a flap, or gular pouch, which is generally used to store fish and other prey while hunting.
In cormorants, the gular skin is often colored, contrasting with the otherwise plain black or black-and-white appearance of the bird. This presumably serves some function in social signalling, since the colors become more pronounced in breeding adults.
In frigatebirds, the gular skin (or gular sac or throat sac) is used dramatically. During courtship display, the male forces air into the sac, causing it to inflate over a period of 20 minutes into a startling huge red balloon.
Because cormorants are closer relatives of gannets and anhingas (which have no prominent gular pouch) than of frigatebirds or pelicans, it can be seen that the gular pouch is either plesiomorphic or was acquired by parallel evolution.
The walrus, some species of gibbon apes, the conus snail, and fictional species, like the snow goblin in Dungeons & Dragons and the great oopik in Star Wars, have a throat sac. Many amphibians will inflate their gular sac to create certain vocalizations to communicate, scare off rivals (to proclaim territory or dominance), and locating and attracting a mate by using their vocal sac to amplify their voice to be heard louder and closer. And some species of lizards may also have a gular fold (and gular scales), the Orangutan, only in males, is the only known ape to have this characteristic.