The skin of birds' feet: Morphological adaptations of the plantar surface

International audience; The skin of the foot provides the interface between the bird and the substrate. Thefoot morphology involves the bone shape and the integument that is in contact withthe substrate. The podotheca is a layer of keratinized epidermis forming scales thatextends from the tarsometatarsus to the toe extremities. It varies in size, shape,amount of overlap and interacts with the degree of fusion of the toes (syndactyly). Astudy of toe shape and the podotheca provides insights on the adaptations ofperching birds. Our analysis is based on micro-CT scans and scanning electronmicroscopy images of 21 species from 17 families, and includes examples with differentorientations of the toes: zygodactyl (toes II and III forward), anisodactyl (toes II,III, and IV forward), and heterodactyl (toes III and IV forward). We show that in thesethree groups, the skin forms part of a perching adaptation that involves syndactyly todifferent degrees. However, syndactyly does not occur in Psittacidae that use theirtoes also for food manipulation. The syndactyly increases the sole surface and mayreinforce adherence with the substrate. Scale shape and toe orientation are involvedin functional adaptations to perch. Thus, both bone and skin features combine toform a pincer-like foot.