Figure 3
From: Closely related gull species show contrasting foraging strategies in an urban environment
(a) Biplot of whole blood δ15N and δ13C for great black-backed gulls (black squares) and herring gulls (black triangles) and potential food sources (grey circles). Differences in δ13C and δ15N between great back-backed and herring gulls were tested for significance using a Wilcoxon-rank sum test (α = 0.05). (b) Simulated mixing region from potential food sources and probability contours. Isotopic positions of gulls with corresponding GPS tracks are shown as filled symbols (squares for great black-backed and triangles for herring gulls), and those without GPS tracks as open symbols. Contour lines are placed at 10% intervals except for the outermost contour, which is at the 5% level.
