What are Great Bustards?

The Great Bustard (Otis tarda) is a large bird in the Bustard family, unrelated to other large bird species such as turkeys or geese. Great Bustards can (and do) fly, and are the heaviest flying animal alive today. Great Bustards can be found across Europe, as far south as Spain and as far north as the Russian steppes. Most members of the Bustard family are smaller than the Great Bustard – only the Kori Bustard and the Great Indian Bustard are of a similar size. Male Great Bustards grow about 30% larger than the females, reaching up to one metre tall and weighing up to 16kg. The heaviest recorded Great Bustard weighed in at 21kg. The conservation status of the Great Bustard is listed as vulnerable, with populations in many countries being in decline. The species became extinct in the UK in 1832.

Appearance

Huge, heavily built and robust but stately in appearance, adult male bustards can be identified by their bulging neck, heavy chest and characteristically cocked tail. Shape is similar to a large goose, but the bustard is much larger with considerably longer legs and a straighter neck.

The head and neck are a pale blue-grey, the body and tail rufous brown with black bars, and underparts white. The wings of the Great Bustard are mostly white with dark primary and secondary feathers.

Males in breeding plumage grow large white moustachial whiskers (20cm long) and become more vividly coloured on their back and tail. They also develop a band of russet coloured feathers on their lower neck and breast, which becomes wider and brighter as they get older.

Size

There is a marked difference in size between males and females, termed sexual size dimorphism. Great Bustards actually exhibit the largest sexual size dimorphism of any bird species and most other mammals, birds, reptiles, amphibians, and fish! Female Great Bustards can be as much as 50% smaller than males.

Males: Standing height 90-105cm. Wingspan 210-250cm. Weight 8-16kg.
Females: Standing height 75-85cm. Wingspan 170-190cm. Weight 3.5-5kg.

Voice

Adults are usually silent but males can sometimes be heard when fighting in breeding season. They use a variety of gruff nasal barks and also a soft “umb, umb” sound, which is sometimes heard as the gular (throat) pouch is inflated and deflated during display. The young also have a number of calls including a high plaintive whistle. This is first heard from the egg prior to hatching and it continues until chicks are several months old.

Taxonomy

Great Bustards belong to the order Gruiformes, within which there are twelve families, including the cranes. The Bustard family, Otididae, contains 25 species in nine genera. The majority of these species are found in Africa, but there are also representatives of the family in Europe, Asia and Australasia.

Otis tarda tarda (Linnaeus, 1758). This is found from Iberia and Morocco, through central and south-east Europe to Turkey, and east to central Siberia. The vast majority of the world population is of this form, which is also the form native to the UK.

There is one other subspecies, Otis tarda dybowskii (Taczanowski, 1874). This occurs in East Asia, from the eastern Altai and Lake Baikal in Russia through Mongolia to northern China. It differs from the nominate form in having a slightly paler head and neck, broader more well defined black markings on the back and a greater number of white tail feathers. The whiskers on adult males are connected by short bristle-like feathers on the central chin.

Common name

It is thought that the word Bustard is derived from ‘Bustarde’ and ‘Bistard’ which date back to at least the fourteenth century, having been recorded as a surname in 1391. Most sources state that this is derived from the Latin avis tarda, meaning slow bird. This became abetarda or betarda in Portuguese, avutarda in Spanish, ottarda in Italian and oustarde and bistarde in Old French. It is suggested that the English is derived from a blend of the two French words with the form Bistard found in some 16th and 17th century sources. Great Bustards had traditional local names in different parts of the country. In Sussex they were called ‘Shepherd’s Wild Turkey’.

Scientific name

The name Otis is Greek for ear, as in ear of wheat or barley. Each spring, male Great Bustards grow whiskers which closely resemble the ears of wheat. The name tarda is Latin, meaning slow. The Great Bustard is often stately but the word tarda is rather surprising as this species is actually rather fleet of foot and has a surprisingly fast flight. In their first official list of British birds, published in 1883, the British Ornithologists Union state that tarda is a “Celtic or Basque word, bearing no relation to tardus = slow”, although they do not say what the word means. It is possible that tarda is in fact the original name from a language spoken in Spain before the arrival of the Romans. On being taken into Latin, it naturally seemed to mean slow.

Population & distribution

Great Bustards have a range stretching across Eurasia, from Iberia and Morocco in the west to China in the east, though their distribution is extremely fragmented and numbers are low in many parts of their range. The world Great Bustard population is estimated to be between 44,000 and 57,000 individual birds. The species has undergone a long-term and marked decline, especially since the early 19th century. This decline has been slowed in the past 20 years by major conservation action in many countries. In that period the European population has increased, driven by a rise in the large Iberian population, and the world population has stabilised.

 

 

 

 

 

 

 

 

The population estimates in the table below are taken from Alonso & Palacin (2010): The world status and population trends of the Great Bustard (Otis tarda): 2010 update (Chinese Birds 2010, 1(2):141-147). This shows that over 50% of the world population of Great Bustards is found in Iberia. The only other substantial population is found in western Russia.  Several countries have small, threatened populations. Some are in the initial stages of recovery, like those in Austria and Germany, thanks to conservation work, but the continuing existence of others, for example in Morocco or Iran, is less certain.

Countries with current breeding records Number of Great Bustards
Austria 199 – 216
Bulgaria 0
China (NW Xinjiang) 400 – 2,400
Czech Republic 0 – 2
Germany 114 – 116
Hungary 1,413 – 1,582
Iran 89 – 161
Kazakhstan 0 – 300
Moldova 0
Mongolia (NE China & SE Russia) 1,500 – 2,200
Morocco 91 – 108
Portugal 1,893
Romania 0 – 8
Russia (European) 8,000 – 12,000
Serbia & Montenegro 35 – 36
Slovakia 0 – 3
Spain 29,400 – 34,300
Turkey 400 – 1,000
Ukraine 520 – 680

The East Asian population of the subspecies Otis tarda dybowskii is thought to total 1,900 to 4,600 birds.

The range of the Great Bustard undoubtedly expanded after extensive clearance of forests by man. It probably reached its maximum extension in the 18th century. A subsequent marked and rapid decline in numbers accompanied by increasing fragmentation of populations has occurred. This is continuing with the conversion of steppe and dry meadows to arable fields, agricultural intensification and persecution.

Behaviour

Great Bustards are highly gregarious birds that form social units termed ‘droves’. Males and females live in separate droves and there is a tendency for birds of the same age to keep together. Large, often loose, flocks form in winter, which may wander in search of food, sometimes joining up with other flocks. Female droves visit groups of displaying males briefly during the breeding season.

Gait is slow and deliberate but bustards are capable of surprisingly fast dashes. Feeding action is a swift pick-up of food from the ground and fast ‘snatching’ of vegetation. They have a very wary nature. They will often withdraw into tall vegetation when alarmed, but never into bushes or trees, and sometimes they will fly away. Flight is between 30-100 m above ground, with an action noticeably regular and uninterrupted. They never glide, but beat their wings slowly and majestically, making rapid progress. Wings are long and deeply fingered appearing mostly white. They are generally silent, unless flushed or threatened at very close range, when a nasal bark is sometimes heard. The lack of an opposable hind claw means they cannot perch, so they are a completely ground-dwelling bird. Their notoriously shy and wary behaviour makes them very difficult to observe.

Food

The Great Bustard is omnivorous, meaning it eats both animal and plant matter. Diet is mainly composed of plants during spring, autumn and winter. Typically they take young shoots, leaves, flowers, ripe and unripe seeds but occasionally also rhizomes, bulbs, berries and fruits. The proportion of animal food varies with season, locality, age and sex of bird, but they are mostly carnivorous in summer. Insects and their larvae predominate but small vertebrates such as voles and lizards are also taken. Has been observed taking items not normally taken by other birds such as poisonous seeds of Hemlock, unripe seeds, beetles with unpleasant taste or defensive chemicals and caterpillars with warning colouration. Young are chiefly insectivorous, but as they grow they increase the proportion of plants eaten.

Movements

Populations are migratory in the east, and dispersive or resident elsewhere. The Iberian population shows least movement although local movements do occur. In central Europe the species is mainly resident but will undergo movements of several hundred kilometres in severe winters with heavy snow. Wintering grounds are often established in areas with extensive cultivation of crops such as oil seed rape. The degree of cold weather movements is not always directly correlated with depth or duration of snow cover, and not every hard winter leads to extensive emigration.

In the former USSR, Great Bustards are often considered truly migratory, except in southern Ukraine where resident. The Ukrainian population is boosted by up to 10,000 birds in the winter, mostly from the Russian Federation. However, recent winter observations of birds wintering in Russia at -30C with deep snow cover suggests that even in hard winters not all migrate. Great Bustards have been reported from Syria and Iraq in winter but whether birds still breed in these countries is unknown.

Habitat

Great Bustards are most likely to have evolved in dry tropical grassland plains, but since man’s extensive forest clearances and cultivation of land, open habitat has increased. Great Bustards are now found across continental middle latitudes, especially the steppe zone, but penetrate into temperate, Mediterranean, marginal boreal and oceanic climates. They favour lowlands, river valleys, and undulating open country, avoiding steep or rocky terrain, deserts, wetlands, forests, and savannas or parklands with more than isolated or small clumps of trees. Although traditionally a bird of expansive grass plains, they have adapted well to modern agricultural landscapes. Arable fields bearing crops such as oil seed rape and lucerne now appear to be more attractive than natural steppe, although farmland areas with high agricultural disturbance near human settlements are often avoided.

Breeding

Females typically become sexually mature from two years of age and males typically from four years. Great Bustards have a mating system termed ‘lekking’. Males compete for females with an elaborate visual display. Females appear to visit several males before copulating and appear to be very selective in their choice of mate. Mating success is strongly skewed, with the majority of matings performed by a small proportion of males at a lek site. No pair bonds are formed and pairings may differ from year to year. During the display, males appear to grow in size and change colour from brown to white. This is done by ruffling the feathers and inflating a special balloon-like structure in the neck called the gular pouch. The wing feathers are twisted forward and fan out, and the tail is cocked right up and over onto the back. The head is drawn onto the back also, as the gular pouch is inflated, pushing the white whiskers upwards. The displaying male usually stands still or stomps his feet and swings his inflated neck.

Nesting and Young

After mating, females disperse to lay their eggs – they do not form nesting colonies. Males play no part in the nesting or care of the young. The incubation and rearing of chicks is carried out by the female alone.

Great Bustards nest on the ground, making a small depression and sometimes lining it with a few pieces of vegetation. Two eggs are normally laid, although occasionally one or three may be laid. Eggs weigh about 150g and average around 80mm tall by 57mm wide. They vary in colour from grey to green or brownish, with darker blotches. The eggs take around four weeks to hatch. Newly hatched chicks are about 20 cm long and weigh about 100g. They are a greyish colour with dark brown or black markings. The chicks are nidifugous, meaning they are able to leave the nest site soon after hatching. Although they can walk almost immediately, the chicks cannot feed themselves for the first few days so the mother feeds them insects bill to bill. As the chicks develop they gradually feed independently for a larger proportion of the time.

Young Great Bustards begin developing their adult plumage at about two 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. Juveniles are independent by their first winter, but normally stay with their mother until the next breeding season.

Mortality

The natural mortality of Great Bustards in the wild is over 80% in the first year. As ground-dwelling birds with a reluctance to fly, they are susceptible to a certain level of predation when feeding, nesting and roosting. Predators of eggs and hatchlings include avian predators such as raptors and corvids (crows) and mammals such as foxes, badgers and hedgehogs. Chicks grow incredibly quickly and by six months are approximately three-quarters full size. The number of predators reduces by this time to typically include foxes and where they occur, wolves and large raptors such as White-Tailed Eagle. Full grown adults, especially those in groups, are normally capable of scaring off, or fleeing safely from these predators.

They are long-lived birds, so those that do make it through the first year usually live on for another 15 or 20 years. In adults, males have a higher mortality rate than females, probably due to fighting during the breeding season and being typically bolder in character.

All photographs © David Kjaer.