Резкое падение численности кудрявого пеликана Pelecanus crispus (Aves: Pelecaniformes) на Урале и в Западной Сибири в 2021 г.

Abstract

The Dalmatian pelican Pelecanus crispus (Bruch, 1832) is a globally rare species. Its extremely local ("point") placement during the nesting period on a few hard-to-reach water bodies distanced far from one another makes it a highly vulnerable species. In the end of the 20th century, the number of the species in Chelyabinsk, Kurgan and Tyumen oblasts steadily grew. This was largely due to the redistribution of individuals from drying reservoirs of the more southern parts of the breeding range to the northern ones against the background of global climate warming. Thus, pelicans stopped nesting in the Svetlinsky Reserve (Orenburg oblast) due to the drought. In the spring and summer of 2021, the first mass deaths of these birds occurred in the history of study in the Urals and Western Siberia. During the observations of seven colonies in Chelyabinsk, Kurgan and Tyumen oblasts using the DJI Mavic-2 Zoom drone, we found that many individuals did not return to the breeding grounds in the spring after wintering, and another part died at the height of the breeding season. As a result, the number of pelicans decreased by 70-80% in some colonies; in others, the proportion of dead birds was less, and some separate colonies were almost not affected at all. At the same time, in the western part of the study area (Chelyabinsk oblast), a significant part of the individuals died outside the breeding grounds, whereas in the eastern part, the birds died mainly in the breeding grounds and at a later time. In Kurgan oblast, the death of birds was noted in May, in Tyumen oblast it was in June. The total number of pelicans in the study area decreased from 1.2-1.4 thousand pairs to about 600 pairs (see the table). Six colonies were preserved; most of them now number 30-50 breeding pairs at best. However, in the study area, the largest colony (and the easternmost in the Okunevo Reserve (Tyumen oblast)) survived almost completely with about 400 pairs of pelicans continuing to breed. No more than 30 individuals died there, and this happened later than in other colonies, in July 2021. The main version of the cause of birds’ mass death is the epizootic of avian influenza which was tested in all samples (n = 5) taken from a colony in Tyumen oblast. Pelicans live in dense flocks all year round, and this could really contribute to the rapid spread of the infection. The facts of the birds’ death in various nesting sites located on a large territory, at a great distance from one another, make it seem that they contracted the virus in wintering areas. However, a number of questions remain unanswered. In particular, it is unclear how the infected birds were able to travel thousands of kilometers to their breeding grounds, why individuals of only one particular species died, why only adults died, and why they died at different times. Maybe, the avian influenza virus tested in the birds’ bodies was low-pathogenic and was not the cause of their death, but it was due to some other factor, such as food poisoning. It might be that the immunity of the birds was weakened by the abnormal heat that came to the study area since mid-May 2021. If the birds died from a highly pathogenic virus, it is unclear why this did not happen immediately after infection (in the wintering areas), but in a long time, at least from May to July. Moreover, the infection with the virus did not prevent the birds from arriving at breeding sites, building nests, laying eggs and starting to incubate. However, influenza viruses are very diverse and continue to evolve rapidly changing their properties and increasing resistance to the environment. Our understanding of the ecological factors favoring emergence and sustainability of these viruses is still limited. More efforts should certainly be made to save such a globally rare species as the Dalmatian pelican. At the moment, a large breeding colony on the territory of Western Siberia (on Tundrovo Lake in the Okunevo Reserve (Tyumen oblast)) remains the main breeding ground of the species in this area. Therefore, the importance of preserving this breeding colony comes to the fore. The article contains 1 Table, 42 References. The Author declares no conflict of interest.