Gaping is a common form of behavior in the animal kingdom, in which an animal opens its

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

widely and displays the interior of its mouth, for any of various purposes.Stephen J. Divers, Douglas R. Mader, ''Reptile Medicine and Surgery'' (2005), p. 168. This may be a form of

deimatic behaviour Deimatic behaviour or startle display means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey anima ...

, colloquially known as a startle display or threat display, as it enlarges the appearance of the animal, and for those with teeth it shows the threat that these represent. Animals may also use gaping as part of a courtship display, or to otherwise communicate with each other. Some animals have evolved features which make gaping behavior more visually effective. For example, " many species of reptile, the oral mucosa may be a bright color that serves to distract the predator". Gaping is part of the shark agonistic display, and is also found in snakes such as the

cottonmouth ''Agkistrodon piscivorus'' is a species of pit viper in the subfamily Crotalinae of the family Viperidae. It is one of the world's few semiaquatic vipers (along with the Florida cottonmouth), and is native to the southeastern United States. As ...

, and in birds ranging from seagulls to puffins to roosters. A number of species of bird use a gaping, open beak in their fear and threat displays. Some augment the display by hissing or breathing heavily, while others clap their beaks. In birds, the muscles that depress the lower mandible are usually weak, but certain birds have well-developed

digastric muscle The digastric muscle (also digastricus) (named ''digastric'' as it has two 'bellies') is a small muscle located under the jaw. The term "digastric muscle" refers to this specific muscle. However, other muscles that have two separate muscle bellie ...

s that aid in gaping actions. In most birds, these muscles are relatively small as compared to the jaw muscles of similarly sized mammals. Both male and female

puffin Puffins are any of three species of small alcids (auks) in the bird genus ''Fratercula''. These are pelagic seabirds that feed primarily by diving in the water. They breed in large colonies on coastal cliffs or offshore islands, nesting in crev ...

s use gaping as a prominent part of their threat display, with "a range of intensities" based on the situation, and with puffins engaging in territorial gape contests, where they mirror each other until one gives up and leaves, or an actual fight occurs. Some animals are named for their tendency to use gaping as a threat display, or for the features that become apparent when making such a display. For example, the cottonmouth is so named because the white lining of its mouth is visible when gaping. Other snakes, such as the Western Massasauga, have been observed to engage in gaping behavior which "appears to be unrelated to any threat".Scott Shupe, ''U.S. Guide to Venomous Snakes and Their Mimics'' (2011), p. 139.

Gallery of images

Cottonmouth Snake, Gaping.jpg, ''A. p. piscivorus'' – gaping is part of the typical

threat display Deimatic behaviour or startle display means any pattern of bluffing behaviour in an animal that lacks strong defences, such as suddenly displaying conspicuous eyespots, to scare off or momentarily distract a predator, thus giving the prey anima ...

, the white mouth giving it the nickname "cottonmouth". Attacking_great_white_shark.jpg, Clear agonistic gaping behavior observed in Great White Shark. Chlamydosaurus kingii.jpg,

Frill-necked lizard The frilled lizard (''Chlamydosaurus kingii''), also known as the frill-necked lizard or frilled dragon, is a species of lizard in the family Agamidae. It is native to northern Australia and southern New Guinea. This species is the only member o ...

faces predators, making itself look big with head frills, gaping, raising its body and waving its tail. Gull Beak IMG 1575.JPG, A

gull Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st century, m ...

's upper mandible can flex upwards because it is supported by small bones which can move slightly backwards and forwards.

References

Ethology Antipredator adaptations {{biology-stub