Binomial regression model showing the functional relationship between the presence of corpora (purple polygon) in female harbour porpoises from the German North Sea and Baltic Sea in relation to their age as determined by GLG.

The filled area indicates the 95% confidence interval of predicted values. The red line within that area indicates the predicted average probability of finding corpora within specimens at the given age; the blue dashed line marks a probability of 50%, with the red solid line indicating the corresponding age based on the intersection of the blue dashed line with the x-axis; samples are indicated as dark grey dots; a purple circle around data points indicates animals below the age threshold showing at least one corpus, an orange circle indicates animals above the threshold showing no corpora; background histogram (orange) shows number of animals (secondary y-axis) across tooth age classes (at 1-year intervals).