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The great bustard (Otis tarda) is in the bustard family, the only member of the genus Otis. It breeds in southern and central Europe, where it is the largest species of bird, and across temperate Asia. European populations are mainly resident, but Asian birds move further south in winter. Portugal and Spain now contain about 60% of the world's population.
Taxonomy and etymology
The great bustard was classified with its scientific name in 1758 by Carl Linnaeus, though the species was referred to as avis tarda in the much older writings of Pliny the Elder, and hence its names in English (from Old French bistarda) and some other languages: abetarda (pt), avetarda (gl), avutarda (es). Otis is an Old Greek name for "bustard". The specific name, tarda, has been traced to an Old Spanish name for "tread", although it has also been used in Latin for "slow" and "deliberate", which is apt to describe the typical walking style of the species.
The male of this huge bird is possibly the heaviest living flying animal. It also arguably the most sexual dimorphic extant bird species, in terms of the size difference between males and females. Going on mass, the only known bird with a higher dimorphism is the green peafowl (Pavo muticus) as the males are apparently near four times as heavy as the female. Among both bustards and all living birds, the upper reported mass of this species is rivaled by that of the kori bustard (Ardeotis kori), which, due to its relatively longer tarsi and tail, is both longer and taller on average and is less sexually dimorphic. In terms of weight ranges reported, the Great Indian bustard (Ardeotis nigriceps) also only lags slightly behind these species. A male is typically 90–105 cm (2 ft 11 in–3 ft 5 in) tall, with a length of around 115 cm (3 ft 9 in) and has a 2.1–2.7 m (6 ft 11 in–8 ft 10 in) wingspan. The male can range in weight from 5.8 to 18 kg (13 to 40 lb). Average male weights as reported have been fairly variable: in Russia, males weighed a median of 9.2 kg (20 lb); in Spain, males weighed a mean of 9.82 kg (21.6 lb) during breeding season and 10.62 kg (23.4 lb) during non-breeding; in Germany, males weighed a mean of 11.97 kg (26.4 lb); and the Guinness World Records has indicated that prior to their extirpation male bustards in Great Britain weighed an average of 13.5 kg (30 lb). The heaviest verified specimen, collected in Manchuria, was about 21 kg (46 lb). In a study in Spain, another giant male tipped the scales at 19 kg (42 lb). Larger specimens have been reported but remain unverified.
The female is about a third smaller in linear dimensions, typically measuring 75 to 85 cm (2 ft 6 in to 2 ft 9 in) in height, about 90 cm (2 ft 11 in) in length and 180 cm (5 ft 11 in) across the wings. The females are roughly one-third the weight of the male. Overall, the female's weight can range from 3.1 to 8 kg (6.8 to 17.6 lb). Like male weights, females weights are quite variable as reported: in Germany, females had a mean weight of 3.82 kg (8.4 lb), in Spain, females had a mean weight of 4.35 kg (9.6 lb) and in Russia, females reportedly had a median weight of 6 kg (13 lb). The latter figure indicates that eastern birds (presumably O. t. dybowskii) are considerably less sexually dimorphic in body mass than in other populations. Perhaps because of this physical sexual dimorphism, there is a skewed sex ratio of about 1.5:1 female to male.
An adult male is brown above, barred with blackish colouration, and white below, with a long grey neck and head. His breast and lower neck sides are chestnut and there is a golden wash to the back and the extent of these bright colours tending to increase as the male ages. In the breeding season, the male has long white neck bristles, which measure up to 12–15 cm (4.7–5.9 in) in length, continually growing from the third to the sixth year of life. In flight, the long wings are predominantly white with brown showing along the edges of the lower primary and secondary feathers and a dark brown streak along the upper-edge of the wing. The breast and neck of the female are buff, with brown and pale colouration over the rest of the plumage rendering it well camouflaged in open habitats. Immature birds resemble the female. The Eastern subspecies (O. t. dybowskii) is more extensively grey in colour in both sexes, with more extensive barring on the back. The great bustard has long legs, a long neck and a heavy, barrel-chested body. It is fairly typical of the family in its overall shape and habitat preferences. Three other bustard species overlap in range with this species: the Macqueen's (Chlamydotis macqueenii), houbara (Chlamydotis undulata) and little bustards (Tetrax tetrax). However, none of these attain the huge sizes, bulky form and plumage coloration of this species. Thus, the great bustard is essentially unmistakable.
Among standard measurements in the Eastern race, males have a wing chord length of 59.5 to 63.5 cm (23.4 to 25.0 in), a tail of 21 to 23.5 cm (8.3 to 9.3 in), a tarsus of 14.2 to 15 cm (5.6 to 5.9 in) and an exposed culmen of 4.1 to 4.7 cm (1.6 to 1.9 in). In comparison, the Eastern female measures 45.5 to 49.5 cm (17.9 to 19.5 in) across the wing chord, has a tail of 17.8 to 21 cm (7.0 to 8.3 in), a tarsus of 11.3 to 12.6 cm (4.4 to 5.0 in) and a culmen of 3.5 to 4 cm (1.4 to 1.6 in), respectively. Standard measurements indicate the nominate subspecies is slightly larger than the Eastern subspecies, in adult males, culmen length is to 9.8 cm (3.9 in), wing chord length to 69 cm (27 in), tail length to 29.5 cm (11.6 in) and tarsal length to 22 cm (8.7 in).
This bird's habitat is grassland or steppe defined by open, flat or somewhat rolling landscapes. It can be found on undisturbed cultivation and seems to prefer areas with wild or cultivated crops such as cereals, vineyards and fodder plants. However, during the breeding season, they actively avoid areas with regular human activity and can be distributed by agricultural practices. Great bustards are often attracted to areas with considerable insect activity.
This species is gregarious, especially in winter when gatherings of several dozen birds may occur. Male and female groups do not mix outside of the breeding season. The great bustard has a stately slow walk but tends to run when disturbed rather than fly. Running speeds have not been measured but adult females have been known to outrun red foxes (Vulpes vulpes), which can reach a trotting speed of 48 km/h (30 mph). However, they can be fairly strong fliers as well, especially during seasonal movements, and can reach speeds of up to 80 km/h (50 mph) in flight. Both sexes are usually silent but can engage in deep grunts when alarmed or angered. The displaying adult male may produce some booming, grunting and raucous noises. The female may utter some guttural calls at the nest and brooded young make a soft, trilling call in communication with their mothers. The Asian and Russian populations of the species are migratory and will gather in large numbers at pre-migratory sites in order to move collectively to winter grounds. In the remainder of the range, such as Central Asia, only partial migrations may occur based on seasonal food availability. In the Iberian Peninsula, bustards that engage in migration seem to choose different periods for movements based on sex. No population is known to use the same grounds for wintering and summering.
The great bustard breeds in March, and a single male may mate with up to five females. Before mating, the males moult into their breeding plumage around January. Males establish dominance in their groups during winter, clashing violently by ramming into and hitting each other with their bills. Like other bustards, the male great bustard displays and competes for the attention of females on what is known as a lek. In this species, the male has a flamboyant display beginning with the strutting male puffing up his throat to the size of a football. He then tilts forwards and pulls his head in so that the long whiskery chin feathers point upwards and the head is no longer visible. He next cocks his tail flat along his back, exposing the normally hidden bright white plumage then he lowers his wings, with the primary flight feathers folded but with the white secondaries fanning out. The displaying males, who may walk around for several minutes at a time with feathers flared and head buried, has been described as a "foam-bath" due to its appearance. All breeding great bustards also moult again from June to September.
One to three olive or tan coloured, glossy eggs (two eggs being the average) are laid by the female in May or June. The nests, which are shallow scrapes made by the female on dry, soft slopes and plains, are usually situated close to the prior lek location. Nests are situated in sparse clusters, with a study in Inner Mongolia finding nests at a minimal 9 m (30 ft) apart from each other. In the same study, nests were placed at mid-elevation on a hill, at about 190 to 230 m (620 to 750 ft). Nesting sites are typically in dense grassy vegetation about 15 to 35 cm (5.9 to 13.8 in), likely for protection against predation, with extensive exposure to sunlight. Eggs weigh about 150 g (5.3 oz) and are on average 79.4 mm (3.13 in) tall by 56.8 mm (2.24 in) wide. The female incubates the eggs alone for 21 to 28 days. The chicks almost immediately leave the nest after they hatch, although they do not move very far from their mother until they are at least 1 year old. Young great bustards begin developing their adult plumage at about 2 months, and begin to develop flying skills at the same time. They practice by stretching, running, flapping, and making small hops and jumps to get airborne. By three months they are able to fly reasonable distances. If threatened, the young stand still, using their downy plumage, mainly sepia in colour with paler buffy streaks, as camouflage. Juveniles are independent by their first winter, but normally stay with their mother until the next breeding season. Males usually start to mate from 5 to 6 years of age, although may engage in breeding display behaviour at a younger age. Females usually first breed at 2 to 3 years old.
This species is omnivorous taking different foods in differing seasons. In northwestern Spain in August, 48.4% of the diet of adult birds was comprised by green plant material, 40.9% was invertebrates and 10.6% was seeds. In the same population during winter, seeds and green plant material compromised almost the entirety of the diet. Alfalfa is seemingly preferred in the diet of birds from Spain. Other favoured plant life in the diet can including legumes, crucifers, common dandelion and grapes and the dry seeds of wheat and barley. Among animal prey, insects are generally eaten and are the main food for young bustards in their first summer, though they then switch to the seasonal herbivorous preferences of adults by winter. Coleoptera (including beetles), Hymenoptera (including bees, wasps and ants) and Orthoptera (including crickets, grasshoppers and locusts) are mainly taken, largely based on availability and abundance. Small vertebrates, including small rodents, frogs, lizards and chicks of other birds, may supplement the diet when the opportunity arises. A 2014 study in the journal PLOS ONE suggests that great bustards may eat blister beetles of the genus Meloe to self-medicate (Zoopharmacognosy).
Great bustards typically live for around 10 years, but some have been known to live up to 15 years or more. The maximum known life span for the species was 28 years. Adult males seem to have a higher mortality rate than females due mainly to fierce intraspecies fighting with other males during the breeding season. Many males may perish in their first couple of years of maturity due to this cause.
Although little detailed information has been obtained of predators, over 80% of great bustards die in the first year of life and many are victims are predation. Chicks are subject to predation by the fact that they are ground-dwelling birds which are reluctant to fly. Predators of eggs and hatchlings include raptors, corvids, hedgehogs, foxes, badgers (Meles ssp.), martens (Martes ssp.), rats (Rattus ssp.) and wild boars (Sus scrofa). The most serious natural predators of nests are perhaps red foxes and hooded crows (Corvus cornix). Chicks grow very quickly, by 6 months being nearly two-thirds of their adult size, and are predated by foxes, lynxes, wolves (Canis lupus), dogs, jackals and eagles. The bold, conspicuous behaviour of the breeding adult male bustard may attract the same large mammalian predators that predate chicks, such as wolves and lynx, while the more inconspicuous female may sometimes be attacked by large eagles. However, predation is rare for adults due to their size, nimbleness and safety in numbers due to their social behaviour.
Occasionally, other natural causes may contribute to mortality in the species, especially starvation in harsh winter months. However, major causes of mortality in recent centuries have been largely linked to human activity, as described below.
The population of this species numbers between 31,000 to 37,000 birds. Between 4,200 and 4,500 are found in east Asia. In recent times, there have been steep declines in population throughout eastern and central Europe and in Asia, particularly in Kazakhstan and Mongolia.
|Native||Afghanistan, Armenia, Austria, Azerbaijan, Bosnia and Herzegovina, Bulgaria, China, Croatia, Czech Republic, France, Georgia, Germany, Greece, Hungary, Iran, Iraq, Italy, Kazakhstan, Kyrgyzstan, Macedonia, Moldova, Mongolia, Montenegro, Morocco, Portugal, Romania, Russia, Serbia, Slovakia, Spain, Syria, Tajikistan, Turkey, Turkmenistan, Ukraine, Uzbekistan|
|Regionally extinct||Algeria, Myanmar, Poland, Sweden, Switzerland, United Kingdom|
|Vagrant||Albania, Belgium, Cyprus, Denmark, Egypt, Finland, Gibraltar, Ireland, Israel, Japan, Korea, Latvia, Luxembourg, Malta, Netherlands, Saudi Arabia, Tunisia|
|Presence uncertain||Lebanon, Pakistan|
Sizeable populations exist in Spain (23,055 birds), Russia (8,000 birds), Turkey (800–3,000 birds), Portugal (1,435 birds) and Mongolia (1,000 birds). Elsewhere, the populations are declining due to habitat loss throughout its range. A sizeable population also exists in Hungary (1,100–1,300 birds) where the Eastern European steppe zone ends, near Dévaványa town and also in the Hortobágy National Park, Nagykunság and Nagy-Sárrét regions. The population is down from a population of 10,000–12,000 before the Second World War.
Threats and conservation status
The great bustard is classified as Vulnerable at the species level. There are myriad threats faced by great bustards. Increasing human disturbance and land privatisation is expected to lead to habitat loss caused by the ploughing of grasslands, intensive agriculture, afforestation, increased development of irrigation schemes, and the construction of roads, power lines, fencing and ditches. Mechanisation, chemical fertilizers and pesticides, fire and predation by dogs are serious threats for chicks and juveniles, and hunting of adults contributes to high mortality in some of their range countries. Agricultural activity is a major disturbance at nest and, in Hungary, few successful nests are found outside of protected areas.
Two very rare albino great bustards from the same nest were killed by electricity cables in Hungary in 2000 and 2003. The bustards, despite their large size, are able to fly at high speed and are often mutilated or killed by the cables, which are placed in Hungary just at their flying height. The electricity companies affected will bury only part of the dangerous cables; the authorities are therefore experimenting with fixing fluorescent "Firefly" devices on the most dangerous cables to provide the birds with warning lights. Bustards are also occasionally killed by collisions with automobiles or by entanglement in wires.
The great bustard was formerly native in Great Britain and a bustard forms part of the design of the Wiltshire Coat of Arms and as supporters for the Cambridgeshire arms. It was hunted out of existence in Britain by the 1840s. In 2004 a project overseeing the reintroduction to Salisbury Plain in Wiltshire using eggs taken from Saratov in Russia was undertaken by The Great Bustard Group, a UK Registered Charity that aims to establish a self-sustaining population of great bustards in the UK. They have laid eggs and raised chicks in Britain in 2009 and 2010. Although the great bustard was once native to Britain, great bustards are considered an alien species under English law. The reintroduction of the great bustard to the UK by the Great Bustard Group is being carried out in parallel with researchers from the University of Bath who are providing insight into the habitat of native great bustard populations in Russia and Hungary. On January 19, 2011 it was announced that the Great Bustard Project had been awarded EU LIFE+ funding, reportedly to the tune of £1.8 million. In Hungary, where the species is the National Bird, great bustards are actively protected. The Hungarian authorities are seeking to preserve the long-term future of the population by active protection measures; the area affected by the special ecological treatment had grown to 15 km2 (5.8 sq mi) by the summer of 2006.
Under the auspices of the Convention on Migratory Species of Wild Animals (CMS), also known as the Bonn Convention, the Memorandum of Understanding (MoU) on the Conservation and Management of Middle-European Populations of the Great Bustard was concluded and came into effect on June 1, 2001. The MoU provides a framework for governments, scientists, conservation bodies and others to monitor and coordinate conservation efforts in order to protect the middle-European populations of the great bustard.
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