A frontal shield, also known as a facial shield or frontal plate, is a feature of the anatomy of several bird species. Located just above the upper mandible, and protruding along the forehead, it is composed of two main parts: a hard, proteinaceous callus and a soft, fleshy
corium. It is thought to play roles in protection, mate identification, sexual selection, and territorial defense.
Composition
The callus is a hard, keratinous section of the frontal plate located highest on the forehead. It is generally more pigmented than the surrounding corium. Underneath the callus is a Malpighian layer of tissue that connects the structure to the maxilla. This layer is supplied with blood via vessel-containing dermal papillae. It has been observed to resemble the texture of calloused human skin. The corium is a thick, dense mass of connective tissue fibers that makes up the largest portion of the frontal plate. It contains layers of cells that aide in enlarging or flattening the structure. The corium may also be pigmented, but is clearly delineated from the callus by size and texture. A posterior muscle attachment and cell layers within the corium allow it to change shape between enlarged, semi-enlarged, and flattened. The cell layers become vacuolated to cause enlargement, and may return to normal to cause flattening.
Function
A strong correlation between frontal plate state and season has been observed. During winter months, the frontal plate remains flattened and small. This may help to protect the tissue from cold conditions. During the breeding season in the warmer months, the frontal plate becomes enlarged as a method to attract mates, and scare away other individuals competing for a mate. The fully enlarged form of the frontal plate can be double the size when flattened.
Territorial males will enlarge their corium and raise the feathers on the back of their neck to appear larger and more threatening to competing males.
Research has also suggested that the shape of the callus serves as an identifying feature for mating pairs. Birds have been observed to show aggression towards another individual in their territory until that individual's frontal plate is fully visible. After recognition, normal pair behavior commences.
It consists of a hard or fleshy plate of specialised skin extending from the base of the
upper bill over the
forehead
In human anatomy, the forehead is an area of the head bounded by three features, two of the skull and one of the scalp. The top of the forehead is marked by the hairline, the edge of the area where hair on the scalp grows. The bottom of the fo ...
. The size, shape and colour may exhibit
testosterone
Testosterone is the primary male sex hormone and androgen in Male, males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testicles and prostate, as well as promoting se ...
-dependent variation in either sex during the year. Functionality appears to relate to protection of the face while feeding in, or moving through, dense vegetation, as well as to
courtship display
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...
and
territorial
A territory is an area of land, sea, or space, belonging or connected to a particular country, person, or animal.
In international politics, a territory is usually a geographic area which has not been granted the powers of self-government, ...
defence.
It is a characteristic of some
water bird
A water bird, alternatively waterbird or aquatic bird, is a bird that lives on or around water. In some definitions, the term ''water bird'' is especially applied to birds in freshwater ecosystems, although others make no distinction from seabi ...
s in the
rail family, especially the
gallinules and moorhens,
swamphens and
coots, as well as in the
Jacana family.
The
watercock's frontal shield is extended above the head into a horn-like protuberance. A bird from a different order, the extinct
Choiseul pigeon, had a blue frontal shield.
Gallery
File:Fulica cristata -Cape Town, South Africa -head -adult-8.jpg , Red-knobbed coot
File:Coot (14012394247).jpg, Eurasian coot
File:Moorhen-beak443.jpg, Dusky moorhen
File:Gallicrex cinerea -Basai Wetlands, near Gurgaon, Haryana, India-8.jpg , Watercock
File:Rotstirn-Blatthuehnchen.jpg, Wattled jacana
The wattled jacana (''Jacana jacana'') is a wader in the family Jacanidae found throughout much of South America east of the Andes Mountains, Andes, as well as western Panama and Trinidad. It is the only species in the Jacanidae family with suc ...
File:PurpleSwamphenHead.jpg , Australasian swamphen
The Australasian swamphen (''Porphyrio melanotus''), commonly known as the pūkeko in New Zealand, is a striking and socially complex bird found in Oceania, including eastern Indonesia (the Moluccas, Aru Islands, Aru and Kai Islands), Papua New ...
See also
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Casque (anatomy)
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Comb (anatomy)
A comb is a fleshy growth or crest on the top of the head of some Galliformes, gallinaceous birds, such as domestic chickens. The alternative name cockscomb (with several #Spelling variations, spelling variations) reflects the fact that combs are ...
*
Crest (feathers)
The crest is a prominent feature exhibited by several bird species on their heads. It is distinct from features such as casques and cockscombs - sometimes erroneously referred to as "crests", which are bony and fleshy structures respectively.
...
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Fecal shield
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Frontal scale
*
Wattle (anatomy)
A wattle is a fleshy Caruncle (bird anatomy), caruncle hanging from various parts of the head or neck in several groups of birds and mammals. Caruncles in birds include those found on the face, wattles, dewlaps, Snood (anatomy), snoods, and earlob ...
References
{{Reflist
Gullion, Gordon W. The Wilson Bulletin Vol. 63, No. 3 (Sep., 1951), pp. 157–166
Bird anatomy
Rallidae