MODERN RENDS IN THE POPULATIONS OF THE SIBERIAN CRANE (<i>GRUS LEUCOGERANUS</i>) AND THE SANDHILL CRANE (<i>GRUS CANADENSIS</i>) (GRUIDAE, GRUIFORMES) IN THE TUNDRA OF YAKUTIA AND CHUKOTKA, BASED ON AERIAL SURVEYS

Abstract

The Sandhill crane has become a common to abundant breeding species in the tundra of northeastern Yakutia, with the ranges of both Sandhill and Siberian cranes presently overlapping widely. Further range expansion of the Sandhill crane to the west and a population increase can assist competition to the stenotopic Siberian crane which is classified as a Critically Endangered species by the IUCN. To assess the dynamics of the Siberian and Sandhill crane populations, we repeated the historical aerial surveys of 1993–1995 along the Arctic coast of Yakutia and Chukotka in 2020 to 2021. Novel methods of our survey included the use of a photo-camera in addition to a voice recorder and a GPS navigator. The survey data were processed using QantumGIS 3.16.5 software. The overlapping area of both crane species expanded significantly in 2020 to 2021 as compared to 1993–1995. The local densities correlate negatively: in those areas where the density of the Sandhill crane increased, the density of the Siberian crane decreased or the latter one disappeared. The Siberian crane disappeared from the western part of the Kolyma Lowland and the Kolyma Delta, where a peak population density of the Sandhill crane has recently been reported. Our data show some concentration of the Siberian crane range in the Yana-Indigirka Lowland. Areas of the maximum density of the two species do not coincide, the distance between their centers amounting to 400 km. The center of the maximum density of the Sandhill crane has shifted to the west by 400 km from the Chaun Lowland to the Kolyma Delta over 28 years, while the numbers remain almost stable. They increased 1.22 times between the aerial surveys and can be estimated at 41,930 individuals in the areas under survey. The density of the Siberian crane increased 5.3 times over the same years, the population numbering 2.086 individuals in the surveyed areas.