Bustards

         

Class: Aves
Order: Gruiformes
Suborder: Otidides
Family: Otidae

Description
Medium size to very large terrestrial birds, with long legs and necks and fairly short straight bills.

Size
15.75–47.25 in (40–120 cm); 1–42.2 lb (0.45–19 kg)

Number of genera, species
11 genera; 26 species

Habitat
Level or gently undulating grasslands, steppes, semideserts, and open savanna woodlands.

Conservation status
Endangered: 3 species; Vulnerable: 1 species; Near Threatened: 6 species

Distribution

Africa, southern Europe, south and Southeast Asia, New Guinea and Australia.

Evolution and systematics
Bustards are linked ancestrally to cranes and their relatives (Gruiformes). Genetic studies place them in their own suborder, Otidides, whose divergence from the Gruides is estimated at 70 million years ago. Although conspicuous courtship displays imply a link with cranes, the evolutionary isolation of bustards finds manifestation in various morphological anomalies. These include the absence of a hind toe and preen gland, hexagonal rather than transverse tarsal scutellation, and unique dense powder-down.
Taxonomic relationships within the family are contested. The large bustards are grouped in Otis, Neotis, and Ardeotis, and these are possibly related to the smaller Chlamydotis and Tetrax. Diminutive Tetrax, long combined with the far larger Otis by taxonomists, might be related to Sypheotides, to which it more closely equates in terms of size, flight-feather modification, and display. Some recent appraisals combine 14 relatively small species within the genus Eupodotis, but an alternative treatment retains only five species in this grouping, separating the remainder into Afrotis, Lissotis, Lophotis, Houbaropsis, and Sypheotides.

Physical characteristics
Bustards combine stout bodies carried horizontally with long legs and necks, the latter supporting flat-crowned heads and short, straight bills. As a result of an exclusively terrestrial lifestyle, they have no hind toe. They tend to escape danger by flying, and consequently their feet are relatively small, and their wings are large and strong. Mature male Otis and
Ardeotis bustards regularly reach over 3.3 ft (1 m) in height,
and as some approach 44 lb (20 kg), they are among the heaviest
of flying birds. 

                   

In these genera, females tend to be twothirds
the height and one-third the weight of their respective
males. In smaller bustard species, the difference in size between
the sexes is less pronounced. Bustard plumage is largely cryptic: the upperparts are brown or finely barred, so that a crouching bird is camouflaged. The underparts are often white in open-country species, and sometimes black in species that inhabit taller vegetation (counter-shading being less of a consideration). Many species have patches of white and black in the wing that are concealed when standing or sitting but conspicuous in flight. Males are generally brighter or more strikingly patterned than females, at least in the breeding season, but sexes are similar in Eupodotis. In Otis, Ardeotis, Neotis, Chalmydotis, Lissotis, and Houbaropsis, males develop filamentous plumes that are used in courtship displays. The most elaborate are in Chlamydotis (elongated erectile piebald plumes on breast, neck, and crown), Otis (white moustachial plumes), and Sypheotides (long bare-shafted, spatulate-tipped cheek feathers).

Distribution
Bustards are confined to the Old World. A glance at patterns of bustard diversity suggests that they originated in Africa, where 21 species occur. Sixteen of these are purely Afrotropical, and another two only fractionally enter the North African portion of the Palearctic region. Within Africa, there are two distinct centers of speciation. One is in East Africa, between the Horn and the Nile, the other is in southern Africa south of the Zambezi. Of four species with chiefly Palearctic distributions, two are widespread in Europe and Asia, with portions of their ranges in North Africa. One is entirely North African; another is almost entirely Asian, extending from Egypt and the Middle East to China (these two forms, the Houbara bustard Chlamydotis undulata and Macqueen’s bustard C. macqueenii, are often treated as conspecific). Three more species are Oriental (all centered on the Indian subcontinent, one with an outlying population in Indochina), and one species is Australasian, occurring in Australia and southern New Guinea.

Habitat
Bustards inhabit temperate and tropical semideserts, grassy plains, and open low-stature woodland. The majority (19 species) are most commonly associated with flat or gently undulating open landscapes, generally with vegetation sufficiently low to allow them a view over long distances. Many African bustards (Eupodotis, Lophotis, and Lissotis) tolerate varying degrees of wooded cover, including acacia woodland and thorny thickets, and the floricans (Sypheotides and Houbaropsis) are regularly found in tall grassland. 

               

A huge area of habitat suitable for bustards has been converted to cultivation, especially in Europe and the Indian subcontinent. Fortunately, many species tolerate nonintensively farmed land.

Behavior
Most bustards are found walking slowly across open terrain. Several species are at least partially gregarious. The great bustard
(Otis tarda) has been recorded in groups of over 50, and nonbreeding aggregations of the little bustard (Tetrax tetrax) can number in the thousands.



 The desert-adapted forms, such as Chlamydotis, are probably the most solitary. 


                   

A few species gather at loose leks. Foraging bustards are regularly found near herds of grazing herbivores. Presumably they benefit from reductions in predation pressure or elevations in foraging success, as they hunt insects disturbed by the mammals. It is unlikely that any bustard species is entirely sedentary, and many are clearly nomadic or migratory.

                         

 Those that breed in Asia undertake long distance migrations to escape harsh winters. The lesser florican (Sypheotides indica) performs regular migrations in response to rainfall in India, and the same is true of several African species.

Feeding ecology and diet
Bustards are omnivorous and opportunistic. Most species have a diet predominately of vegetable matter. They eat fresh shoots, flowers, and leaves of herbaceous plants; excavate for soft roots and bulbs; and take fruit and seeds when available. In cultivated areas they consume a variety of crops. Insects are also an important food, at least seasonally. 

                      


The timing of breeding tends to synchronize chick emergence with maximum insect abundance. Although beetles and grasshoppers are the main invertebrate prey items, many other arthropods are taken if available. Bustards also consume small vertebrates such as reptiles and rodents, particularly those killed or injured in bush fires or traffic. Bustards can thrive without water for long periods, but drink freely when water is available.

Reproductive biology
The breeding season tends to coincide with periods of high rainfall. At its outset, males of many species perform magnificent displays, often from traditionally favored locations. In general, pair bonds between male and female bustards appear to be absent, as females visit displaying males and then leave to incubate the eggs and raise the chicks alone. 

                 

Sexual maturation is slowest and sexual dimorphism most pronounced in species with dispersed leks or solitary territorial males: males take up to six years to reach full size and possess plumage ornamentation absent in females. The displaying great bustard selects an elevated site and
then inflates his gular sac and raises his tail, exposing white undertail-coverts. The inner secondaries are then twisted over and fanned so that, at the height of his splendid performance, having apparently turned himself inside out, the gleam of white plumage is visible several miles away. The kori bustard (Ardeotis kori) grossly inflates his neck plumage, cocks his tail, and emits a low booming call. Many smaller bustards, particularly those that inhabit taller vegetation, incorporate vertical display leaps or short flights into courtship behavior so that they are visible from a distance.
The nest is a bare scrape into which one to six (usually two to four) eggs are laid. Incubation is 20–22 days in the little bustard, 24–25 days in the great bustard, and presumably between these extremes in all other species. Incubation starts with the first egg, leading to asynchronous hatching. The precocial young (hatched covered with down and open eyes) can usually walk after a few hours.

Conservation status
In the face of agricultural intensification, pesticide use, hunting, and disturbance, bustard populations are falling and their distributions shrinking. Four species are currently considered Threatened: the widespread great bustard and all three bustards from the Oriental region.

                       

 Six more bustards are treated as Near Threatened: little, Denham’s (Neotis denhami), Nubian (N. nuba), Houbara, little brown (Eupodotis humilis), and blue bustard (E. caerulescens). [This assessment treats Houbara and Macqueen’s bustards as conspecific.] All remaining large species are suffering declines and extinction at the local level. The most threatened species are the two floricans and the great Indian bustard (Ardeotis nigriceps). They are confined to India and Indochina, where heavy hunting pressure and degradation of suitable habitat has savagely reduced their populations.
Although small numbers of each of these species breed and survive within protected areas, their future hangs in the balance. In general, bustards are at greater risk than many animals because populations in all but the very largest reserves are not viable. Low population densities, and their nomadic or migratory lifestyles, mean that current protected area networks do not comfortably meet their needs.

Significance to humans
Bustards bring economic and ecological benefits. Depredation of insect plagues and other crop pests by bustards improves agricultural productivity, and they are likely to play an important role in seed dispersal. In return, most species have suffered grievously at the hands of man. A heavy toll is exacted in
many
regions by hunting, to the point that Asian populations face a serious threat of extinction. The most significant method is the use by Arabian dignitaries of trained falcons to hunt bustards. The modern version of “traditional” entourages, equipped with teams of falcons and the latest technology, trawl across Middle Eastern deserts for the Macqueen’s bustard. With numbers falling, the falconers have expanded their activities throughout North Africa, partly shifting their attention to Arabian (Ardeotis arabs) and Nubian bustards. A similar scale of persecution is reported from Cambodia, where Bengal floricans (Houbaropsis bengalensis) are a favorite source of food.