Figure 1.

Seasonal variation in the proportion of oystercatchers which specialized on feeding on Manila clams (open circles) and of those which ever included Manila clams in their diet (filled squares). The total numbers of birds observed in consecutive months are 7, 12, 19, 23, 21, 23, 24 and 29 (Σ=158). The lines depict the binary logistic regression equations between date and the proportions (p) of birds, specializing on Manila clams (dashed line; log(p/(1−p))=−3.339+0.373^* months after August, G=10.92, n=158, d.f.=1, p=0.001), and those including Manila clams in their diet (solid line; log(p/(1−p))=−2.882+0.419^* months after August, G=19.41, n=158, d.f.=1, p<0.001).