Pattern of Pads and Folds in the Foot of European Oscines (Aves, Passeriformes)

Abstract

AbstractA comparative study of pads and folds in the foot is made on 56 passerine species, classified in 18 families or subfamilies of the suborder Oscines. A basic pattern of thirteen pads is recognized: twelve in the digits, each related to one phalanx; the thirteenth in the central part of the foot, ventral to the trochleas of tarsometatarsus. Certain pads in the anterior digits are divided in species with long and narrow pads. The number of folds varies, even in the same species, but a basic pattern is recognized. There is one fold at each joint. Except for the fold at the distal joint in the four digits, these folds are comparable with pads in certain non‐Passerifor‐mes. The folds at the proximal phalanx of the third and the fourth digit are interpreted as reduced pads. Some folds are separated parts of phalanx pads. – Most passerine birds have this basic pattern of pads and folds, clearly adapted to a life on branches or on twigs. Certain species, exemplified by Alauda arvensis, Plectrophenax nicalis, Certhia familiaris, and Regulus regulus, have different morphology of pads and folds, depending on a reduced number of papillae, and being adaptations to life on the ground, on tree trunks, or on very thin twigs. Relatively few papillae occur in certain species that winter in temperate or cold climates. This means a reduced area of contact with the substrate and is probably important in heat regulation by reducing the conductive heat flow through the papillae to the substrate.–The pads and folds have a restricted value for the classification on family or subfamily level.