a) Assignment of individual feather SI value to five isotopic clusters based on δ13C and δ15N (according to [21]) and percentage of raster cells assigned to four isotopic clusters within individual 50% and 75% KDE.

Grey shading indicates corresponding assignment of individual feather stable isotopes and KDE.灰色阴影代表单个羽毛稳定同位素与核密度估计（Kernel Density Estimation，KDE）的对应赋值。