Gular Skin

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.

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.