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  • Language: Русская версия
Section: Biology
One Flew East, One Flew West...

One Flew East, One Flew West...

Birds and viruses have always coexisted. The problem of “avian influenza,” recently exhibited before the public in a rather terrifying form, with a certain assistance of mass media, has been known to the experts for a long time. As early as in the 1970s–1980s, the examination of migratory birds with respect to their infection was part of a large-scale research into their migratory behavior and migratory flyways

Mass spring and autumn bird migrations have always attracted the attention of naturalists. However, for a long time there have been few attempts to study them seriously.

The new era in the study of bird migrations commenced in 1899, when the Danish teacher C. Mortensen began to label birds by attaching numbered metal rings with indication of the country to their legs. Although a more modern labeling technique—satellite transmitters—appeared, the banding of birds is still one of the main methods used in studying bird migrations as it is economical, easy to use, and bird-friendly (the rings don’t weigh much).

As early as in the 1950s, it was found that birds and their exoparasites may play an important role in maintaining and spreading a number of pathogens. Some years later, civil and military aviation began sustaining losses from the collisions of jetliners with migratory birds. The study of regular seasonal bird migrations became a topical problem for many countries, and in 1963 the World Health Organization addressed research institutions of many countries with the request to promote the studies of migratory birds.

A Migratory Klondike

About 450 bird species inhabit the south of West Siberia, and over 90 percent of them move on a regular pattern twice a year — from the sites of nesting to winter sites in fall and in the opposite direction in spring. Migratory flyways of some species are short enough amounting to hundreds of kilometers; however, the majority of species fly over several thousand kilometers.

The banding of birds in our region was commenced in 1949–1951 by researchers of the Institute of Animal Systematics and Ecology, Siberian Branch of the Russian Academy of Sciences (called “Biological Institute” at that time). In the early 1970s, the Institute proceeded to a systematic study of the West Siberian migratory birds, mainly on the site of Baraba forest–steppe adjacent to Lake Chany. This site was selected because the forest–steppe of West Siberia is concurrently a tremendous “incubator” where hundreds of thousand baby birds hatch during the nesting period and a vast “railway station” where an even larger number of the birds nesting in taiga and forest–tundra stop during their flyover.

A special importance of the West Siberian forest–steppe and steppe for aquatic birds is determined by the richness of its water basins and moors. The biological capacity of these mainly shallow basins is severalfold higher than the capacity of the lakes located to the north in taiga. That is why many migratory birds in spring and fall stop in the forest–steppe for 10 to 20 days to replenish their depot fat before the further rush.

Birds need grounds rich in protein feed and shelters for another important “deed”, for molting. The majority of birds change their feathers annually. The results of banding demonstrated that the ducks that nest at a distance from two to three thousand kilometers molt at the basins of Baraba!

Despite the common opinion that birds migrate from the south to the north in spring and back in fall, some birds migrate in a longitudinal direction. For example, the lapwing, a mass sandpiper species nesting in the south of Siberia, spends winter in Western Europe: France, Belgium, the Netherlands, and Italy. Some species of our ducks—northern shoveler, pochard, and others (by the way, they are among the most probable vectors of avian influenza) also winter in Europe.

Migration is an intricate thing

The results of bird banding have shown that the summer–fall migrations of certain species in the south of West Siberia start as early as 20–30 days after the spring migrations. What are the reasons for such a long, actually permanent migration? A detailed study of the sandpiper’s flight in the West Siberian forest–steppe demonstrated that the sex–age differences play the key role in migratory behavior.

In all the sandpiper species, the summer–fall migration starts with the adult individuals and ends with the young birds. Also, the sandpipers of different sex migrate at distinct times. For example, the male species are the first to fly in certain groups of sandpipers, and the females in the others. The order of the migration of adult birds is determined by the degree of their participation in hatching and brood rearing. For instance, the male ruffs are not involved in breeding their offspring, and they form about 90 percent of the migrants before mid-July, whereas the females mainly fly in August.

Siberian ornithologists have banded overall about 150,000 birds and received about 1,500 messages about the whereabouts of “their” labeled birds and about 2,500 messages about the birds banded in other sites.

Such time and spatial separation of various sex–age groups, leading to their relative isolation during the migration period, is aimed at a decrease in the intra- and interspecies competition for feed resources in the post-nesting period, which is important for keeping the birds fit.

On the light wings

During the last decades, ornithologists, parasitologists, and virologists have conducted an integrated examination of birds at many key sites of their flyways and nesting places. This has expanded our knowledge about the involvement of birds in the circulation and dissemination of various infectious agents.

It was found that birds are the main carriers of various pathogens of viral, bacterial, fungal, and protozoal natures, as they are involved in the spreading of “avian” diseases, such as ornithosis and avian influenza, as well as in maintaining the foci of tularemia, plague, and other diseases dangerous for humans. By the beginning of the 1980s, scientists isolated from migratory birds over 60 species of the arboviruses alone, transmitted to vertebrates by bloodsucking arthropods! Out of the 60, 15 species are capable of causing human diseases, including life-threatening ones. Among these diseases are the widely known in Russia tick-born and Japanese encephalitides, Omsk and Crimean hemorrhagic fevers, as well as exotic diseases such as Q, Sindbis, Tyaginya, and West Nile fevers.

Migratory birds form massive gatherings at most favorable wintering regions and stopover sites, thereby increasing the probability of exchanging viruses and other pathogens and the chance of their subsequent spread over large distances. Consequently, the foci of viral diseases can be formed on these territories involving the natural strains carried from afar by migratory birds. In this particular way, West Nile fever was brought in 1999 to the USA, which in the following years caused several dozens of human deaths.

In this country, integrated studies of migratory birds were essentially reduced since the beginning of the 1980s due to economical reasons. Evidently, the present situation requires the resumption of bird migration monitoring with participation of ornithologists, virologists, epidemiologists, and other experts. This will allow us to understand the patterns of formation of the natural foci of infections transmitted by birds, and will provide scientific grounds for reliable disease prevention at minimal spending and, last but not least, will not damage natural populations. Our planet should not be deprived of its “light wings”…

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