Fig. 7From: Origin and cross-century dynamics of an avian hybrid zoneProbability density distibutions of cline center and cline width parameters estimated across 1000 bootstrap samples of specimens for the 1911 (red), 1956 (blue), and 2010 (green) time periods. Both morphological PC1 and chroma show a shift in cline center and a reduction of cline width over timeBack to article page