Figure 1.

Sexual size allometry in New World blackbirds (Icterinae). (a) Standardized size dimorphism (log male wing length−log female wing length) versus male size among 103 out of 105 species in the subfamily. Larger species tend to be proportionally more size dimorphic. (b) Log male wing length versus log female wing length plotted from the same sample of species, with the reduced major axis (regression type II) slope calculated. An allometric slope of 1.22 indicates strong positive allometry, i.e. Rensch's rule.