Fig. 6From: Origin and cross-century dynamics of an avian hybrid zoneVariation in morphology and coloration of males over c. 130Â km across the Ramphocelus hybrid zone in historical and recent specimens. a-f Circles are values for individual specimens; dark lines are clines for traits and periods in which parameters were estimated using Hill functions, with shading indicating 95% confidence intervals around cline estimates. g, h Estimates of cline centers at each time period and their confidence limits estimated using bootstrap samples, revealing coincident eastward movement of the hybrid zone over time as indicated by both traits (colors as in a-f)Back to article page