The marginal effects of the predictors on habitat suitability ofA. erythropus (i.e. occurrence probability responds to changes in
a specific explanatory variable while other covariates are assumed to be
held constant as mean) were presented in Figure 5. The response curves
showed that the effects of environmental factors on the occurrence ofA. erythropus were strongly nonlinear.
For topographic variables, the probability of A. erythropuspresence declines with increasing elevation up to 500 m, with locations
higher than 500 m elevation were virtually devoid of A.
erythropus (Fig 5A). Also, the response curve of LDFG indicated that
the geese prefer relatively flat sites (Fig 5I). In terms of bioclimatic
variables, the probability of A. erythropus presence increases
with precipitation of the warmest quarter to around 55 mm and mean
temperature of the warmest quarter to around 14oC,
after which there is a sharp decrease (Fig. 5B, Fig. 5D). Human
disturbance also influences summering habitat, with suitability
increasing the further the site is from human settlement (Fig. 5F). The
response curve of habitat occurrence probability to distance from rivers
(Fig. 5C) suggests that the geese were highly dependent on wetlands and
riparian areas (Fig. 5C). Within the riparian zone, the summering
habitat suitability decreases sharply with increasing distance from
water courses, and after about 4.5 km virtually no birds are found.A. erythropus generally prefers land cover types waters (code
210) and shrubland (120; Fig. 5G). The modeling results suggest that the
probability of occurrence increases with land productivity range (Fig.
5E) and homogeneity (Fig. 5H).