Mass death of swans in the Răut river basin

The mute swan (Cygnus olor) and the whooper swan (Cygnus cygnus) are vulnerable species, included in the Red Book of the Republic of Moldova (2015). They are large, robust and heavy birds with long and thin necks. Body weight is 9 kg in females and 12 kg in males, wingspan reaches 2-2.5 m. The swans are the largest water birds and are among the largest flying birds.

The mute swan is widespread in Europe and Asia. In the Republic of Moldova, it can be found practically in all water bodies. In recent years, about 800 hatchling pairs have been evaluated at the nesting site.

The Black Sea basin is an important wintering area for swans from the northern regions of the European continent and the Russian Federation. Traditionally, the most important wintering places in the Republic of Moldova are on the Dniester river – between Naslavcea and Soroca, the Dubăsari reservoir and downstream of it; on the Prut river – the Costești-Stânca lake and the lower Prut sector. In the past 10 years, when mild winters with temperatures above freezing were recorded, the waters of many water bodies, such as small rivers, lakes and ponds, did not freeze or only partially froze. In these conditions, several thousand of swans can be observed during the winter, which find accessible food sources on the water bodies and adjacent sectors.

Migratory birds, especially ducks, geese and swans are the natural source of bird flu, but they are also the most resistant to infection. In recent years, cases of swan mortality have been reported in various regions of Europe, especially during the winter period, when temperatures do not drop below the freezing point.

In the last month of 2023, the death of over 300 swans was reported in the Răut river basin, and about 10 cases of bird flu were officially declared. Such high mortality in a short period of time cannot be the result of the avian influenza virus alone. Probably, the mass death of swans could be caused by pesticide poisoning, following the consumption of vegetal food from the surrounding agricultural lands. This fact is confirmed by the survival and satisfactory physiological condition of other species potentially carriers the avian influenza virus – species of ducks and geese. However, it is recommended to avoid contact of domestic birds with wild migratory species, as domestic birds are much more susceptible to infections carried by wild species, including avian influenza virus.
 

Dr. Assoc.Prof. Victoria Nistreanu