Results

Potential summering range of the East Asian sub-population of A. erythropus

The mean training AUC of the 100 models was 0.9510 suggested these models are very useful (Swets 1988) for predicting the summering range of A. erythropus . The standard deviation of AUC was very small (0.0007) indicating the models were stable. Moreover, the mean testing AUC was 0.9356 (SD = 0.0739), which was comparable to the training AUC, suggesting excellent predictive power of the fitted model (Lobo et al., 2008).
The average of summering distribution prediction of the 100 models was presented in Figure 3. The most suitable habitats are located along the coasts of the Laptev Sea, primarily the Lena-Delta, in the Yana-Kolyma Lowland, and smaller lowlands of Chukotka with narrow strips extended upstream to catchments of major rivers such as the Lena, Indigirka, and Kolyma (Fig. 3). The binary map (Fig. 4) produced using the criteria of minimum training presence threshold indicated that 36.44% of the study area was suitable summering habitats.
Lowland wetlands including large deltas, estuaries, tundra, and swampy floodplains (i.e. floodplain contains numerous ponds and shallow lakes), which extend from the Lena Delta at the west to the Kolyma River at the east, provide the most extensive and continuous breeding ground forA. erythropus in our study area (Figs. 3 and 4). This is particularly the case for the very large Lena Delta (~29,000 km2, Schneider et al . 2009), where the predicted summering habitats include tundra together with numerous interlaced channels and lakes (Dutta et al . 2006).
Most of predicted breeding habitats are covered by a range of plant types including grasses, sedges, herbs, as well as abundant mosses and lichens. This tundra vegetation is also characterized by widely spaced shrubs (e.g. Betula nana (s.l.), Dushecia fruticosa and several species of Salix ) (Yurkovskaya 2011). Such tundra vegetation along major rivers within the taiga biome also have potential to be suitable habitat (Fig. 3).