Sex determination of adult Humboldt Penguins using morphometric characters

The Humboldt Penguin (Spheniscus humboldti) is one of the most endangered and least-studied species of penguins. Studies of its breeding ecology are needed to develop management plans for its conservation, and sex determination is essential to measure certain reproductive parameters. Humboldt Penguins, like other species of penguins, showed sexual size dimorphism, with males being heavier and larger than females. One discriminant function was derived from external measurements of 297 wild adult Humboldt Penguins of known sex (146 females and 151 males) at Punta San Juan, Peru. The sex of 95% of these birds could be correctly determined using the discriminant function D₁ = -38.98 + 3.16(WH) + 3.69(BL) where WH is width of the head and BL is bill length. In addition, the sex of 91% of the birds were correctly classified by means of the bill length using the univariate function D₂ = -6.31 + BL. In both equations, if D > 0 the bird was classified as male, if D < 0 it was a female, and if D = 0, the sex could not be identified. The discriminant function D₁ was not accurate to sex a group of captive Humboldt Penguins (71% successfully classified) because there were differences in size of the head between wild and captive birds. However, we obtained 83% of cases successfully classified using the function D₂ as bill length was similar between wild and captive birds. The discriminant function may not be applicable to other wild and captive populations of Humboldt Penguins.