Flickr - Dario Sanches - FRANGO-D'ÁGUA-COMUM (Gallinula galeata) (3)

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 fore ...

. The size, shape and colour may exhibit

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...

-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, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...

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,

swamphen ''Porphyrio'' is the swamphen or swamp hen bird genus in the rail family. It includes some smaller species which are usually called "purple gallinules", and which are sometimes separated as genus ''Porphyrula'' or united with the gallinules pro ...

s 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 The watercock (''Gallicrex cinerea'') is a waterbird in the rail and crake family, Rallidae that is widely distributed across Southeast Asia. It is the only member of the genus ''Gallicrex''. Taxonomy The watercock was formally described in 17 ...

's frontal shield is extended above the head into a horn-like protuberance. A bird from a different order, the extinct

Choiseul pigeon The Choiseul pigeon (''Microgoura meeki'') is an extinct species of bird in the pigeon and dove family, Columbidae. It was endemic to the island of Choiseul in the Solomon Islands, although there are unsubstantiated reports that it may once ha ...

, had a blue frontal shield.

Gallery

File:Fulica cristata -Cape Town, South Africa -head -adult-8.jpg ,

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,

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 which is a resident breeder from western Panama and Trinidad south through most of South America east of the Andes. Breeding The wattled jacana lays four black-marked brown eggs in a floating n ...

File:PurpleSwamphenHead.jpg ,

Australasian swamphen The Australasian swamphen (''Porphyrio melanotus'') is a species of swamphen (''Porphyrio'') occurring in eastern Indonesia (the Moluccas, Aru and Kai Islands), Papua New Guinea, Australia and New Zealand. In New Zealand, it is known as the pu ...

References

{{Reflist Gullion, Gordon W. The Wilson Bulletin Vol. 63, No. 3 (Sep., 1951), pp. 157–166 Bird anatomy Rallidae

Composition

Function

Gallery

See also

References