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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.
File:Fulica cristata -Cape Town, South Africa -head -adult-8.jpg ,
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. The size, shape and colour may exhibittestosterone
Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of male reproductive tissues such as testes and prostate, as well as promoting secondary sexual characteristi ...
-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 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 coot
Coots are medium-sized water birds that are members of the rail family, Rallidae. They constitute the genus ''Fulica'', the name being the Latin term for "coot". Coots have predominantly black plumage, and—unlike many rails—they are usually ...
s, 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
Red-knobbed coot
The red-knobbed coot or crested coot, (''Fulica cristata''), is a member of the rail and crake bird family, the Rallidae.
It is a resident breeder across much of Africa and in southernmost Spain on freshwater lakes and ponds. It builds a nest o ...
File:Coot (14012394247).jpg, Eurasian coot
The Eurasian coot (''Fulica atra''), also known as the common coot, or Australian coot, is a member of the rail and crake bird family, the Rallidae. It is found in Europe, Asia, Australia, New Zealand and parts of North Africa. It has a slaty-bla ...
File:Head of Eurasian coot.jpg, Eurasian coot
The Eurasian coot (''Fulica atra''), also known as the common coot, or Australian coot, is a member of the rail and crake bird family, the Rallidae. It is found in Europe, Asia, Australia, New Zealand and parts of North Africa. It has a slaty-bla ...
File:Gallicrex cinerea -Basai Wetlands, near Gurgaon, Haryana, India-8.jpg , Watercock
File:Rotstirn-Blatthuehnchen.jpg, Wattled jacana
File:PurpleSwamphenHead.jpg , Australasian swamphen
See also
*Casque (anatomy)
A casque is an anatomical feature found in some species of birds, reptiles, and amphibians. In birds, it is an enlargement of the bones of the or the skull, either on the front of the face, or the top of the head, or both. The casque has been h ...
* Comb (anatomy)
A comb is a fleshy growth or crest on the top of the head of some gallinaceous birds, such as domestic chickens. The alternative name cockscomb (with several spelling variations) reflects the fact that combs are generally larger on cock birds t ...
* Crest (feathers)
The crest is a prominent feature exhibited by several bird and other dinosaur 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 structur ...
* Fecal shield
* Frontal scale
Frontal scale refers to the scales of a reptile which lie in the general region of the forehead of a snake, more specifically between the eyes and to the anterior of this area. These are analogous to the ''frontal bone'' on a human which correspo ...
* Wattle (anatomy)
A wattle is a fleshy 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, snoods, and earlobes. Wattles are generally paired struc ...
References
{{Reflist Gullion, Gordon W. The Wilson Bulletin Vol. 63, No. 3 (Sep., 1951), pp. 157–166 Bird anatomy Rallidae