Climate impacts on distribution of Great Bustards and White-naped Cranes

Scientists at Dauria International Protected Area (DIPA) studied birds in the area from the Kherlen River in the south to the Ingoda and Shilka Rivers in the north, and from the sources of the Onon River in the west to the low reaches of the Argun River in the east. This research has produced extensive data on changes in abundance, distribution, and propagation success of many species of birds in Dauria in relation to climate changes. The most interesting results were obtained for Great Bustard (Otis tarda dybowski) and White-naped Crane (Grus vipio).

Multiple census studies, verbal reports from hundreds of herders and hunters, interviews of villagers, and analysis of literature sources made it possible to describe the dynamics of Great Bustard abundance from the 1960s to the present and White-naped Crane for a slightly shorter period. Researchers also analyzed weather data in Transbaikalia over the same time periods, leading to important conclusions about the relationships between bird numbers and climate.

Changes were seen in bird habitats when wet and dry periods alternated. Lakes and floodplains alternately ran dry in droughts and were filled in wet periods. Vegetation changed in response to availability of moisture. Abundance and distribution of birds changed as well. The overall dynamics of bustard and crane populations were similar. During wet periods birds were more abundant in the steppe zone but declined in forest-steppe. In contrast, dry periods showed the opposite trends. The summer population density of birds may change quickly (by factors up to four and more times within two years). The highest changes in abundance were seen in the steppe where, unlike in forests, habitat conditions can change from favorable (in wet years) to unsuitable (in dry years).

Numbers of nesting birds are much more stable and change slowly compared to numbers of non-nesting species. Immature birds are the most mobile part of the population as they are not bound to a breeding territory. This is why they are the first to leave unsuitable sites and occupy other parts of the region. This was especially characteristic of Swan Goose, Anser cygnoides.

The research showed the existence of small-scale (within the region) and large-scale (in the vast area in Dauria and Eastern Asia) circulation of bird populations. This was attributed to adaptation of the species to the natural processes of almost constant change in habitat conditions in Dauria and the Amur-Heilong River basin. During dry years the most favorable conditions were in the relatively wet zone of steppe-forests and during wet years the best habitats were on the dry steppes.

Knowledge of the relationship between bird numbers and climate conditions enabled predictions of the most significant risks for cranes and bustards during unfavorable periods. The movement of bustards from Mongolian steppes to Russian forest-steppes during dry periods is accompanied by an increase in poaching. For white-naped cranes and many other species of waterfowl during dry years a big problem is disturbance by people and domestic cattle. In Dauria, cattle farming is very developed and grazing sites and human settlements are tied to sources of fresh water. In dry years people and their cattle concentrate near the remaining water bodies (which are crane habitats) and this increases the frequency of disturbance to birds. Also in dry years the number of spring steppe fires increases, causing losses in bird populations. Because of these factors, bustards, cranes, and other rare birds of Dauria require special protection measures in years of unfavorable habitat conditions.

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