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.