Do river polynyas serve as temperature oases for the Brown dipper and the Solitary snipe in northeastern Asia?

The present study examines the temperature conditions experienced by the Brown dipper (Cinclus pallasii Temminck, 1820) and the Solitary snipe (Gallinago solitaria Hodgson, 1831) during their wintering on river polynyas in an extremely cold region of Asia, the mean January temperatures in coastal areas being −25… −20°C, in continental areas, −45… −40°C. In the air layer adjacent to the water, the mean daylight hours’ temperature gradients are substantial. At 1 cm above the water, the temperatures are observed to be 13–15°C higher than background temperatures, while at an elevation of 10 cm, this increase is only 2–2.5°C. At an elevation of 100 cm, the warming effect is not observable. The observed increase in temperature during daylight hours appears to render a negligible impact on both species, as evidenced by the consistency of their behaviour under different weather conditions. It seems reasonable to surmise that the overnighting of both snipe and dipper in snow and ice niches plays significant roles in determining the feasibility of their habitation in the extreme conditions. The temperature in these niches is approximately 1.5–1.8 times higher than the background temperature in both regions. The northern boundary of sightings of the wintering birds studied is situated at a considerable distance south of the northern limit of the mass development of polynyas. The length of daylight hours, the magnitude and period of low air temperatures (the more northerly the colder and shorter the day) restrict the wintering range of the snipe to the rivers of the Pacific basin. The dipper is known to venture further into the continent than the snipe, and it would appear that its range extends beyond the currently documented limits, due to the paucity of research conducted in the region.