Family Bustards (Otididae)

Vulnerable

Great Bustard (Otis tarda)

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Taxonomy

French: Grande Outarde German: Großtrappe Spanish: Avutarda euroasiática
Taxonomy:

Otis Tarda

Linnaeus

, 1758,

Poland

.

In past, birds of C Asia awarded race korejewi, but extensive overlap with nominate. Two subspecies recognized.

Subspecies and Distribution
  • O. t. tarda Linnaeus, 1758 – N Morocco and Iberia, Germany, Austria and Hungary, and S Ukraine; remnant populations elsewhere in E Europe; breeds also in Turkey and W Iran, and from SW Russia to Kazakhstan and NW China, wintering from SE Europe, S Turkey and Syria through S Azerbaijan and N Iran to Turkmenistan, Uzbekistan and NW Afghanistan.
  • O. t. dybowskii Taczanowski, 1874 – SE Russia, Mongolia and NE China, wintering in C & E China.
  • Descriptive notes

    Male 90–105 cm, 5800–18,000 g; female 75–85 cm, 3300–5300 g; wingspan male 210–260 cm, female 170–190 cm. Breeding male has upperparts barred black and gold, with broad white patch on closed wing, tail as back with broad black subterminal bar and white tips; head and foreneck pale blue-grey shading into white and then vinous russet on lower hindneck, sides of lower neck and breast; long whitish barbs point back from chin; undersides white; bill dull grey, legs olive brown to dull grey. Non-breeding male lacks chin-barbs, and has entire neck and breast pale grey. Female similar to, but considerably smaller than, non-breeding male. Juvenile similar to adult female, but has more buff on head and neck, and upperparts less distinctly barred. Race dybowskii has head and neck slightly paler grey and upperparts more distinctly barred, but barely distinct from nominate and geographical limits unclear.

    Drawing by Norman Arlott
    Descriptive notes:

    Male 90–105 cm, 5800–18,000 g; female 75–85 cm, 3300–5300 g; wingspan male 210–260 cm, female 170–190 cm. Breeding male has upperparts barred black and gold, with broad white patch on closed wing, tail as back with broad black subterminal bar and white tips; head and foreneck pale blue-grey shading into white and then vinous russet on lower hindneck, sides of lower neck and breast; long whitish barbs point back from chin; undersides white; bill dull grey, legs olive brown to dull grey. Non-breeding male lacks chin-barbs, and has entire neck and breast pale grey. Female similar to, but considerably smaller than, non-breeding male. Juvenile similar to adult female, but has more buff on head and neck, and upperparts less distinctly barred. Race dybowskii has head and neck slightly paler grey and upperparts more distinctly barred, but barely distinct from nominate and geographical limits unclear.

    Drawing by Norman Arlott
    Descriptive notes:

    Male 90–105 cm, 5800–18,000 g; female 75–85 cm, 3300–5300 g; wingspan male 210–260 cm, female 170–190 cm. Breeding male has upperparts barred black and gold, with broad white patch on closed wing, tail as back with broad black subterminal bar and white tips; head and foreneck pale blue-grey shading into white and then vinous russet on lower hindneck, sides of lower neck and breast; long whitish barbs point back from chin; undersides white; bill dull grey, legs olive brown to dull grey. Non-breeding male lacks chin-barbs, and has entire neck and breast pale grey. Female similar to, but considerably smaller than, non-breeding male. Juvenile similar to adult female, but has more buff on head and neck, and upperparts less distinctly barred. Race dybowskii has head and neck slightly paler grey and upperparts more distinctly barred, but barely distinct from nominate and geographical limits unclear.

    Voice

    Rather silent. Both sexes produce a short, nasal bark as an alarm call or when excited. Downy chicks and fledglings have a range of whistling and trilling vocalisations#R. In addition, the gular pouches of displaying males resonate to produce a hollow, muffled 'umb umb' sound#R.

    Habitat

    Associated with flat or rolling open short-grass plains, usually clear of trees, and agricultural land. In  SW Iberia males especially make seasonal use of very open 'savanna'  Cork Oak Quercus suber and Holm Oak Q. ilex dehesas and olive groves . Insect- and flower-rich grassland and pasture provide important habitat in spring and summer, fields of stubble are favoured in late summer and autumn, lucerne in winter, but a high diversity of low-intensity land use and lack of disturbance are generally important for year-round needs.

    Closer examination reveals sexual as well as seasonal changes in habitat use. In  southern Portugal (and more widely in Iberia) seasonal differences in selection patterns generally parallel changes in estimated food availability. Stubbles and stream margins are selected by all bustards during the post-breeding period, whereas cereal and fallow fields are selected in winter. During the breeding season, males select fallow fields more than other habitat types, whereas females select cereal fields. Habitat selection seemed to be influenced by habitat availability, with birds showing stronger selection for preferred habitats in the areas where they are less available. Since Great bustards use different habitat types throughout the agricultural year it is advisable that habitat management promotes a rotational crop system that includes cereal and fallow fields#R.

    Food and feeding

    Mainly plant material and invertebrates, although small mammals, amphibians and nestling birds sometimes taken. Key plant families consumed include composites, legumes, crucifers and grasses, while the chief animal food is insects of the orders Orthoptera and Coleoptera. A high proportion of cultivated plants is utilized from late summer through to winter, with green matter increasingly important from midwinter into spring, and insects from spring into late summer. Winter oilseed rape is an important resource for birds wintering in eastern Europe, in Austria and Hungary#R. There are differences between males and females: in C Spain, although both sexes are mostly herbivorous, consuming legumes when available, males consume fewer arthropods but of significantly larger size than females; males show higher dietary diversity than females, except during the post-mating season; the mean dietary overlap between sexes is 0·7, one of the smallest known values among birds#R. Increased planting of unirrigated legumes has been linked to population increases in Spain#R.

    Consumption of blister beetles (Meloidae), which produce cantharidin,  a highly toxic compound distasteful to most birds, has been reported in Spain. Consumption of these beetles is especially high among males during the mating period. It has been suggested that the anti-microbial and anti-helminthic properties of cantharidin give males cleaner cloacas to display to inspecting females at leks. Male bustards ritually show their cloacas to females during displays and a clean cloaca may act as a reliable indicator of male quality#R

    Breeding

    Laying in April–May, also June in colder NE parts of range. Nest on ground with or without scrape, occasionally with fragments of grass stems and crop stems as lining. Nearly always 2–3 eggs (1–4); incubation c. 25 days; chicks cinnamon-pink to pale buff, with sepia streaks and other markings; fledging period 30–35 days, although full size reached at 80–120 days, which is also probably the minimum period of dependency. First breeding at 5–6 years in male, 2–3 years in female.

    Annual productivity in a large (700 females) and well-studied population at Villafáfila, NW Spain, has been found to be low, averaging 0.14 chicks reared per adult female, with high interannual variability (0.04–0.29). There population productivity is positively correlated with winter (October– March) precipitation prior to each breeding season, and negatively correlated with the number of days of rain during the hatching period. Reproductive success is higher in females older than six years than in younger birds. Females with a higher than average breeding success tend to breed successfully in years of both low and high population productivity, whereas those with lower than average breeding success do so only in years of high productivity#R. An additional study in NW Spain, covering a more extensive area (over 7000km²) inhabited by nearly 10,000 birds – some 20% of the global population –, found a pre-breeding density of 1.39 birds/ km². Mean productivity was 0.24 chicks per female but was highly variable, being significantly lower in the most densely populated plots. The overall sex ratio was 1.35 females per male during the pre-breeding period. Productivity related positively to areas holding small fields and a high interspersion of land uses. Density and productivity were negatively affected by river density and altitude, and seasonal density variation was positively correlated with human population density#R.

    Movements

    The Iberian birds are largely sedentary or dispersive. Studies of the dense population at Villafáfila, Zamora, NE Spain have shown that juvenile males typically travel further than females, dispersing on attaining independence and eventually establishing territories at leks 5–65 km from their natal areas; females from this population typically settle 0.5–5 km from their natal sites#R. Nevertheless, studies of wing-tagged and radio-marked adult females from this population have found four different movement patterns: females that migrated between breeding and wintering areas (20%) females that only left their year-round home range area to mate (32%), females that migrated from a wintering-mating area to a nesting-summering area (16%), and females that stayed all year round within a relatively small home range area (32%). All females displayed fidelity to their nesting and wintering areas, and most also showed fidelity to their leks#R

     

    Long-term tracking studies have found that the migratory behaviour of Iberian birds is both flexible and culturally transmitted. Female migratory behaviour is not fixed individually. For every age class 15–30% of females changetheir migratory pattern between consecutive years. Migrant females tend to remain sedentary in years when they have dependent young to attend. Immature females usually acquire their migratory behavior by learning from the mother in their first winter or by social transmission from other migratory females in their second winter. The summer migratory behaviour of immature males is learned from adult males; their age-related increase in migratory tendency is associated with greater integration in flocks of migrant adult males. These results show that within the partial migration system, cultural transmission mechanisms, either mediated by kin or not, and individual condition, may contribute to shape the migratory tendency#R.

     

    Adult males in Iberia may be sedentary or may travel to summering areas after nesting. A sample of 22 radio-tagged male Great Bustards from the Madrid region all travelled to postbreeding areas up to 167 km away from their leks. Departures from leks occurred between May and July, with most birds moving northeast to summering areas. Approximately 47% of the males spent only the summer away from their leks, returning to leks between September and December. Other males overwintered in areas located to the southeast, returning to lek sites between January and March#R. In general, males from more southern sites travel further, up to 250km, and to higher elevations. Summering sites are often in taller vegetation than used for nesting and include sunflower fields and areas with scattered small trees, such as holm oak dehesas and olive groves; these are thought to offer some respite from the summer heat, that may affect the heavy males more than the females#R. Although summering areas are generally within the breeding range some birds may travel further occasionally, appearing in northern Spain or even in SW France#R#R

     

    Movements elsewhere are less well known. The small and endangered populations of Germany and Hungary move west or southwest in hard winters in response to snow cover especially, but then unfortunately suffer high mortality#R. Further east, populations on the lower Volga basin, Russia, are mostly migratory, wintering in eastern Ukraine; the males appearing to move over shorter distances, probably related to degree of maturity; females travel up to 1100 km#R. The wintering population in southern Ukraine was estimated at 8000 birds during 1998–2000, most of them in southeast Kherson and eastern Crimea#RMigratory in Asia, where southward shifts occur, generally over limited distances, from August to early winter, with birds returning March–April. However, some clearly travel much further; three females were tracked through satellite telemetry from their breeding grounds in N Mongolia to wintering grounds in Shaanxi province, China, some 2000 km distant#R.

    Status and conservation

    VULNERABLE. CITES I and II. World population estimated in 2010 to be 44,100–57,000 individuals, with c. 57–70% in Spain, 15–25% in European Russia, 4–10% in China, Mongolia and SE Russia, 3–4% in Portugal, 3% in Hungary, 1–2% in Turkey and smaller numbers in ten other countries#R. Continued declines reported for some countries (e.g. Turkey, Iran, China) but total numbers have not significantly decreased worldwide post-2000, particularly because the very large Iberian population has recovered following a hunting ban, since 1980 in Spain. The core Spanish population of Castilla y León, Spain, increased by 34% during 1998–2008, to number 14,025 birds in 2008, nearly half the Spanish population; the increase has been attributed to the spread of unirrigated legumes, crops that are promoted by agri-environmental schemes#R. Only 6–10% of world total is apparently still decreasing, mostly due to agricultural intensification, other causes of habitat degradation and, locally, also illegal hunting and collision with powerlines. A small fraction of the world population (3–4%), is clearly (Germany, Austria) or apparently (Hungary) increasing, due to management and conservation measures. Finally, 19–22% of world total has an uncertain status, due to inaccurate current or past censuses which prevent establishing reliable population trends#R.

     

    Breeds in Morocco (c. 100 birds), Portugal (1900), Spain (29,400–34,300), Austria (c. 200), Czech Republic (0–2), Germany (c. 100), Slovakia (0–3), Hungary (c. 1400–1580), Serbia and Montenegro (35–36), Romania (0–8), Turkey (764–1250), Iran (89–161), Russia (8000–12,000), Ukraine (520–680), Kazakhstan (up to 300), Mongolia (c. 1000) and China (c. 500–3300)#R#R. Range is becoming increasingly disjunct following rapid declines and some extinctions throughout E & C Europe: in Czech Republic, Slovakia, Romania, Bulgaria, Poland and Moldova, as well as in Russia, Kazakhstan, Mongolia, Turkey, Iran and Morocco, and in most of eastern range.

     

    A survey in Morocco in spring 2015 found bustards at only two of seven leks occupied ten years before and only 40–44 birds were found, a 40% decline over same period#R; this population may be extinct within 20 years unless conservation measures are implemented urgently#R. The populations of the Iberian Peninsula and Morocco comprise three main genetic units corresponding to Morocco, the northeastern part of Spain, and the rest of the Iberian Peninsula, rendering the isolated Moroccan population a separate management unit of high conservation concern#R.

     

    Some range contraction, with local recent recovery in Spain, witnessed in Iberia#R and Hungary. Nevertheless, the species has increased in Hungary, Austria, Germany and Iberia#R. Recently extinct in Poland, Bulgaria and Yugoslavia; last bred in France 1863, and Sweden and Greece respectively middle and end of 19th century. Extinct in England in 1832 but a reintroduction project began on Salisbury Plain in 2003 initially using chicks imported from Russian Federation#R; breeding has occurred here annually since 2007 but the number of egg-laying females has never exceeded four and few have fledged young#R. Bred in Azerbaijan until 1940s or 1950s, and formerly wintered in considerable numbers with flocks of 150–200 birds recorded in 1930s; few sightings nowadays, and total wintering population may number only a few tens to a few 100s.

     

    Throughout range, irrigation and agricultural intensification (the first promoting the second, and the second leading to sterilized monoculture) are chief threats; also pesticide use, electric cables, illegal hunting, overgrazing and disturbance. Vehicular traffic has been found to be a principal source of disturbance locally, unlike farming and shepherding activities#R. Destruction of nests and chicks during crop treatment and harvesting is substantial. A European action plan was published in 1996 and updated in 2009#R and an action plan for E Asian populations in 1998#R. Agri-environmental and land management programmes have been successfully implemented in Spain, Portugal, Austria, Hungary, Germany and Serbia. Artificial incubation and chick-rearing projects  established in Germany and Hungary since the 1970s#R. A LIFE Nature project for the species was implemented in Hungary during 2004–2008 with aim of increasing in-situ protection of the species, and other LIFE projects have been implemented in Spain, Portugal, Germany, Austria and Slovakia#R.

    Recommended citation

    Collar, N. & Garcia, E.F.J. (2018). Great Bustard (Otis tarda). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/53712 on 21 July 2018).