Description and Identification


The bird bearing the name Great Bustard (Otis tarda Linnaeus, 1758) belongs to the Family Otitidae, Order Gruiformes. It is a steppe-inhabiting bird which has adapted its biotope demands to agricultural lands and pastures in Europe. The Great Bustard is globally endangered, classified as vulnerable by Collar et al. 1994, and is listed in the Annex I of the EC Birds Directive, Annex II of the Bern Convention, Appendix I of the Bonn Convention and Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).



 

Biology of the species

 

BIOTOPES


The original steppe-like biotopes have been, to a great extent, transformed into intensively used agricultural lands. Since the second half of the 20th century, due to biotope changes and intensive agricultural production, the Great Bustard has inhabited substitute habitats. It prefers open landscapes with steppe-like biotopes largely made of pastures mixed with low crops (wheat, barley or alfalfa). In winter, the populations usually stay on agricultural lands with lucerne or colza, occasionally on set-aside lands or grasslands.


NESTING


The Great Bustard nests on the ground in spots with a favourable plant coverage. In cultivated landscapes, the nest are located most often in crop, lucerne or pea monocultures. The nesting spots, chosen by the females, are usually close to display sites – open fields with a lower vegetation in agricultural areas (often winter crops). In original steppe conditions (i.e. in Hungary), the Great Bustard nests in permanent grasslands with a height guaranteeing enough shelter for the sitting (nesting) female. For successful breeding, the species requires a minimum disturbance.
The nest is only a shallow pit on bare ground. From late April till August, the female lays usually 2 eggs (rarely one or even three, more eggs are exceptional). The eggs hatch in 25-27 days. The Great Bustard female is very sensitive to any disturbance, especially in the early incubation period. If disturbed, it is very likely to abandon the eggs.
The chicks are taken care of exclusively by the female, which leads them for about 6-7 weeks, till they start to fly. Many females with juveniles gather for winter to larger flocks.


FOOD


The Great Bustard is rather demanding when it comes to food – it requires a variety of food sources. It mostly feeds on plants, occasionally even small animals, depending on the availability of food during the year. If having a choice, it prefers animals (mostly large insects or small vertebrates). For the Great Bustard, the insects are the main source of proteins and other nutrients necessary for reproduction and for the growth of the chicks in the first months.
The chemical treatment of crops often results in a dramatic decrease of large insect species, while small vertebrates serve only as supplements to diet.
In spring and summer, the plant-based diet includes fresh buds, leaves, flower buds, fleshy fruits and seeds of field crops and weeds.
In the past 4-5 decades, along with the overall transformation of the landscape, the solitary trees and stands of trees have been removed (especially the maybushes, wild pears and cherries, oaks, mulberries and sweetbriers). This led to a significant decrease in the availability of vitamin or nutrient sources for the Great Bustard in the autumn time. In autumn and winter, the Great Bustard feeds on winter crops and cabbage-like plants, especially on their seeds scattered after harvest on non-ploughed stubbles. In wintertime, the animal-based diet is usually made up of small terrestrial mammals (voles).

 

Distribution in Europe



GLOBAL DISTRIBUTION


The Great Bustard is distributed in Europe and Asia between the 35 a 55° of northern latitude. The European subspecies Otis tarda tarda lives in areas ranging from the Pyrenees to southwest Morocco all the way to Siberia. The Asian subspecies Otis tarda dybowskii occupies the range from the Eastern Altay Mountains to Mongolia. Although having a significant global distribution as a species, the nesting sites of the Great Bustard are very unevenly distributed.


DISTRIBUTION IN EUROPE


In numbers, the European population of the Great Bustard includes about 50% of the global population. Almost half of the European population, estimated to have about 31.000 – 36.000 birds, is concentrated in the Iberian Peninsula. Large flocks live in Spain, Russia and Turkey. According to estimates, the Hungarian population counts about 1100 – 1200 birds, while the Austrian totals at 74 – 140 birds.
From the mid seventies, a dramatic decrease in abundance is being observed in most Central European populations.
In Western and Central Europe, the populations of the Great Bustard are non-migrating.

 


 

 

Distribution in Slovakia

 

 

Published data on the Great Bustard show the rapid decrease in its abundance in Slovakia. In the years 1890-1900, the abundance was estimated to be 2400 birds, while data from 1956 counted 1165. Later, in 1973, the estimates varied between only 410-693 birds. After 1975, the population was fragmented into very small flocks and the Great Bustard was observed only on the Danubian Plain (Podunajská nížina). The only exceptions included the year-round presence of 1-3 birds in Nitrianska pahorkatina, an illegal shot of 1 bird near Svätoplukov village and occasional Great Bustard observations near Mojmírovce village. The presence of the Great Bustard near Kvetoslavov and Lehnice villages was proven till the mid-eighties. However, in the nineties, the data showed a critical decline in population numbers in Slovakia, the only observations made in Trnavská pahorkatina and Podunajská rovina.
In Slovakia, the last nesting was observed in 1994, in the border area southwest of Bratislava.  At the end of the nineties, the nesting population was estimated to be only 5-10 females. There were Great Bustard observations reported from Borská nížina, Podunajská rovina, Trnavská pahorkatina and Hronská pahorkatina in the migration period.

 

Threats and Reasons for Decline


LOSS OF FAVOURABLE BIOTOPES

The rapid decline in Great Bustard populations is directly linked to substantial changes of the habitat structure. The native steppe biotopes have been transformed, to a great extent, to large-scale agricultural lands of intensive use.


HIGH MORTALITY

The high mortality of the Great Bustard is caused mostly by its predators (especially juvenile mortality), collisions with overhead power lines (adult mortality) and by long-lasting winters with a massive snow coverage. Due to long-lasting food unavailability in winter, otherwise stable Great Bustard populations can be forced to migrate. The migration has its risks: the populations might end up in areas with unfavourable conditions, or even a few birds can get lost or die, which leads to further losses.

DISTURBANCE
The Great Bustard is sensitive to any disturbance, especially during display, mating, nesting and in wintertime, when food is sparse. The main sources of disturbance are connected to human activities like game hunting, agriculture and recreation.




Conservation Status

 

The Great Bustard is a legally protected species according to both Slovak and international legislation. It is listed on various protection lists: in the Annex I of the EC Birds Directive, Annex II of the Bern Convention, Appendix I of the Bonn Convention and Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). The current conditions for the protection of this bird in Slovakia are not favourable. 



 

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