Рисовые поля юга России: феномен зимовки больших подорликов

Abstract

Prior to our research, only single cases of wintering of the Greater Spotted Eagle (Aquila [Clanga] changa, GSE) in the south of Russia were proved. Wintering of the GSE on the Prikubanskaya plain was first proved for an adult female from the Estonian breeding population, who spent three winters (2018/19, 2019/20, and partially 2020/21) in the same area of the Krasnodar Territory, near the city of Abinsk (Väli et al., 2021; Mischenko et al., 2022). The second case of wintering on the Prikubanskaya plain of a GSE tagged by a transmitter in the north of the Moscow region (the young bird named Oduvanchik) was noted in 2020/2021, also thanks to GPS/GSM telemetry (Mischenko et al., 2021). In 2020 Oduvanchik, after pronounced migration in the south direction, from 21/09 to 23/11 stayed in the area of the city Slavyansk-on-Kuban (Krasnodar Territory). Then he migrated to the western part of the Republic of Adygea, where he stayed for the winter. He spent the winters of 2021/22 and 2022/23 in the same area. On 17–22/11/2021 and 22–25/02/2022, in order to visually detect other GSEs not tagged with transmitters, we conducted a survey of the area of the Prikubanskaya Plain located between the Varnavinsky water reservoir in the west, Krasnodar water reservoir in the east, the city of Slavyansk-on-Kuban in the north, and the city of Abinsk in the south. During the November survey, three birds were visually recorded. During the February survey of this area, in addition to the bird, which, judging by the comparison of the coordinates reported by the transmitter and the observation spot, was most likely Oduvanchik, we visually registered 10 GSEs, 5 of them were recorded simultaneously (Mischenko et al., 2022). Thus, it can be argued that a previously unknown area of stable wintering of GSEs was formed on the territory of the Prikubanskaya plain, which was localized with the help of GSM/GPS telemetry and subsequent targeted field studies. Habitats which were constantly visited by Oduvanchik and Estonian eagle and where all the other birds were visually marked are mainly represented by systems of rice fields with a network of channels. The development of the Kuban floodplain (which began in the mid-1970s) and the creation of a rice-planting system led to a radical change in the entire landscape of the Kuban and, as a consequence, to a change in the conditions of existence of Brown Rat (Rattus norvegicus). A uniform alternation of earthen ramparts, convenient for burrowing and movement of brown rats, rice fields, as well as channels on which even in winter these rodents find food – all this contributes to the year-round habitation of the brown rat outside human buildings and the high density of its settlements in rice fields (Rylnikov, Karaseva, 1985). The number of rats in rice fields is many times higher than in natural habitats. Thus, on the banks of the Kuban limans, the number of rats per 100 linear meters was only 0.1–0.2 individuals, whereas on the shafts of rice fields it was 50–100 times higher: up to 10 or more individuals (Karaseva et al., 1986). At the beginning of September, a full preharvest discharge of water is carried out from rice fields. In November – April, the spatial distribution of Brown Rat populations in rice fields acquires a pronounced mosaic character, showing a tendency to crowding, in accordance with the distribution of places convenient for overwintering. During this period, these rodents are concentrated on certain areas of rice fields (with an area 200–300 hectares), where the feeding conditions are most favorable – usually these are places where there is a lot of under-threshed straw left in the fields (Rylnikov, Karaseva, 1985). Rats feel good on rice paddies even in relatively harsh winters, with a decrease in temperature to –5° and the formation of a stable snow cover up to 10 cm. Usually at this time rats openly move on the surface of snow (Karaseva et al., 1986). In winter, Mallard (Anas platyrhynchos), Rook (Corvus frugilegus), and Wood Pigeon (Columba palumbus) feed on rice fields (Mischenko et al., 2021; Lokhman, unpublished). However, flocks of these birds are present here irregularly. We assume that the high number, concentration, and constant availability of brown rats throughout the autumn-winter period are one of the main reasons for the formation of a stable wintering area of GSEs in the rice systems of the Prikubanskaya plain. One of the main tasks of further research is to identify limiting factors and potential threats to eagles wintering in this territory.