Materials and methods

Study Area

The study area was in northeast Siberia, extending eastwards from Olenyok R (119.2 E) to the watershed between the Pacific and Arctic drainage basins, including Republic of Sakha, Magadanskaya Oblast and Chukotskiy Autonomous Okrug. A. erythropus was never reported in in the Arctic Archipelagos, these island areas are excluded in our study.

Surveys in West Chukotka, Russia

During July-August 2002-2019 surveys were undertaken along rivers and lake habitats in the area of 19,260 km2 of assumedA. erythropus range in Chukotka (Figure 2). Brood-rearing adultA. erythropus with their brood or flocks of molting adultA. erythropus were counted during downstream travel in a motorboat from the upper reaches of rivers, which were reached by helicopter. A description of the study area and survey results of 2002-2010 have been previously published (Solovieva and Vartanyan 2011). No A. erythropus were found on lakes and only surveys along rivers have been used in this study (Figure 2). Positions and numbers ofA. erythropus were given as (1) middle point and peak number for each river from surveys in multiply years; (2) middle point and number per river from single survey for the rivers surveyed once. As rivers of the study area are relatively small (up to 320 km) and uniform by habitat type, we considered each river as one data point for the niche modelling. These surveys provided 11 records for the model comprising eight breeding records and three molting records.