Statistical analysis
The random sampling procedure in the null model was repeated 1000 times,
thus generating 1000 simulated wintering distributions for each
population. Each time, climate was extracted and seasonal niche overlap
was calculated in the same way as for the observed wintering
distributions. We then calculated the rank of the observed seasonal
niche overlap among the 1000 simulated ones. Ranks were rescaled between
0–1 and their distribution was tested for skewness towards low values
(indicating seasonal niche tracking) by one-sample Kolmogorov-Smirnov
tests against a uniform distribution.