Fig. 2From: The bare head of the Northern bald ibis (Geronticus eremita) fulfills a thermoregulatory functionRelationship between the perceived red colour intensity of the bare head skin of Northern bald ibises and Tsurf of the head. Red colour intensity is quantified in a scale from 1 to 3. Each symbol colour corresponds to one of the 11 birds that were included in the study. The line is the regression lineBack to article page