Galliform Anatomy: A Dozen Key Facts

What is a galliform?

Order Galliformes is a large, diverse taxonomic group with a worldwide distribution (Fig 1). More than 250 species have a chicken-like appearance and short, rounded wings.

Gallinaceous birds

Figure 1. Gallinaceous birds. Upper left: Brahmas chicken (Gallus gallus), photo by JumpV; Upper right: Bobwhite quail (Colinus virginianus), photo by Steve Maslowski/USFWS; Lower left: White-tailed ptarmigan (Lagopus leucura), photo by Peter Plage/USFWS; Lower right: Spruce grouse (Falcipennis canadensis), photo by Wilson Hui.

Many gallinaceous species, such as grouse, quail, partridge, pheasant, turkey, and chickens, are economically important to humans due to farming or hunting. Exactly when the chicken was first domesticated is uncertain but there is evidence the Chinese kept domestic poultry around 2000 B.C. Domestic fowl are generally believed to have originated from jungle fowl. Turkey (Meleagris gallopavo) are native to North America. The heaviest gallinaceous bird is the turkey. This unusual bird has a heavy body paired with a thin neck, small head, and long legs. Wild turkey flocks are found in open woods with fields or clearings and flocks may contain up to 60 birds (Fig 2).

Wild turkeys

Figure 2. The domestic and wild turkey are the same species: Meleagris gallopavo. Image by Dr. S. Orosz.

TWELVE CLINICALLY SIGNIFICANT FACTS

If you are comfortable with psittacine anatomy and physiology, then many features of gallinaceous birds will be familiar. LafeberVet has listed twelve interesting and clinically significant facts about galliform anatomy and physiology:

    • Many features of the galliform gastrointestinal tract should be familiar to the companion parrot veterinarian.

Galliforms possess a pointed, triangular beak and a long, slender, non-protrusible tongue. Galliforms also have a complex or well-developed crop for food storage. The stomach includes a well-developed ventriculus or gizzard. Grit material is frequently present within the ventriculus.

 

Well-developed ceca

Gallinaceous birds possess a well-developed ceca and in fact most research on avian cecal function comes from Order Galliformes. The ceca are generally long and slender, and grossly they appear very similar to intestines. Cecal size increases or decreases depending on the amount of dietary crude fiber.

Ceca are particularly well-developed in herbivorous grouse and snowcocks. Celluloytic bacteria have been found in the ceca of black grouse (Tetrao tetrix), hazel grouse (Bonasa bonasia), ruffed grouse (Bonasa umbellus), capercaillie (Tetrao urogallus), willow ptarmigan (Lagopus lagopus), rock ptarmigan (Lagopus rupestris), and turkey. Unlike most gallinaceous birds, the satyr tragopan (Tragopan satyra), and pin-tailed sandgrouse (Pterocles alchata) have ceca that are sacculated or have diverticula.

 

Gastrointestinal flora

Normal gastrointestinal flora in the gallinaceous bird includes Gram-negative bacteria like Escherichia coli. For this reason, fecal gram stain cytology is rarely performed as a screening test.

 

Sexually dimorphism

Male galliforms tend to be larger. In many species, the male has ornamentation, is more colorful, or is patterned differently. (Fig 3).

Ring neck pheasant

Figure 3. The male ring-necked pheasant (Phasianus colchicus) is a strikingly colored bird, while the female ring-necked pheasant is brownish and uniformly patterned. Image by Benimoto.

Cloacal sexing is also possible in day old chicks, Visit Mother Earth News or Science Blogs for more information.

 

Unique skin appendages

No review of galliform anatomy would be complete without this list of vocabulary terms:

      • Comb: A fleshy bulge on top of the head (Fig 4)
      • Wattle: Thick pendant-like appendages at either side of the base of the beak and the upper throat. Wattles are usually much larger in male birds (Fig 4).
Wattle and comb

Figure 4. Comb (small arrow) and wattle (arrowhead) in a Plymouth rock chicken (Gallus gallus). Image by Thomas Pix.

      • Spurs: A bony projection originating from the tarsometatarsus and covered by keratinized epidermis in many cocks. When present in hens, spurs are poorly developed, often with no osseous component. Cock spurs are often sharp and can easily cause injury. Spurs are absent in cracids, Central and South American birds like guans, curassows, and chacalacas as well as grouse.

      • Snood: A fleshy piece of skin located just above the beak in the turkey. Also known as the “front caruncle” (Fig 5).
      • Caruncles: Fleshy bulges on featherless parts of the head and neck of turkeys (and some ducks) (Fig 5).
Turkeys snood caruncle

Figure 5. Major caruncles (thin arrow) and snood (arrowhead) in turkey (Meleagris gallopavo). Image by I. Taylar. Click image to enlarge.

      • Brood patch: Many galliforms develop a vascular thickening on the ventral thoracic skin. Feathers are temporarily lost over the brooding spot or brood patch during incubation allowing body heat to be directly transferred from the hen to the eggs.
      • Helmet: Males of many curassows and guans possess a brightly colored, fleshy knob or a bony casque or helmet on top of the head.

 

Normal feather release

Like many columbids, grouse (family Tetraonidae) undergo a normal, stress-induced physiologic release of feathers when attacked by predators. This fact seems fairly esoteric, until one is called upon to catch up and restrain one of these species—then it is extremely clinical relevant!

 

Short, rapid bursts of flight

Although often able to fly shortly after hatch, gallinaceous birds normally fly at low levels using a high-frequency wing flap that causes them to tire rapidly. Flight is often limited to gliding for short distances.

The only true migratory galliforms are the common quail (Coturnix coturnix) and Japanese or coturnix quail (Coturnix japonica).

 

Variable presence of a preen gland

A uropygial or preen gland is present in most gallinaceous birds. Domestic fowl have one secretory duct opening; some species have two papillae.

The preen gland is absent in rump-less or tail-less breeds of domestic fowl (like some Aracaunas), peacock pheasants (genus Polyplectron), and the argus pheasant (Argusianus argus).

 

Ornamental plumage

Onamental feathers in male birds can originate from different plumage, including retrices or tail feathers (many pheasants), chin feathers (capercaillies), or tail coverts (peafowl) (Fig 6). Tail coverts are the (normally short) feathers that sit at the base of the tail.

Male peacock displaying feathers

Figure 6. The ornamental feathers of the peacock or male Indian peafowl (Pavo cristatus) are widely believed to be tail feathers, but are in fact tail coverts. Image by M. Berndt.

 

Precocial young

All gallinaceous chicks are nidifugous, which means they can ambulate and self feed at hatch.

 

Four of five toes

Most gallinaceous birds have four toes, however some chicken breeds like the Silkie chicken have five toes.

 

Tracheal loop

An elongated trachea is present in some galliform species: chachalacas and various other cracids, ptarmigans, capercaillies, and some guineafowl. In two members of the genus Guttera, most notably the crested guineafowl (G. pucherani), the tracheal loop sits inside a hollow furcula or “wishbone”.

 

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