Variability in Body Pterylosis, with Special Reference to the Genus Passer

Abstract

PTERYLOGRAPHY, the study of avian feather tracts, is an old field of ornithology, rich in history but comparatively neglected in recent years. The first recorded observation that feathers are distributed over a bird's body in specific patterns predates Linnaeus (Scherren, 1903), but not until the early 19th century studies by C. L. Nitzsch was pterylography established as a branch of avian anatomy. Nitzsch made the fundamental descriptive studies in the field and gave it much of the terminology still used today. He described the pterylosis of many hundreds of species, and built a system of classification upon those studies. His System der Pterylographie, compiled and published posthumously in 1840, has never been surpassed in scope and remains the basic reference in the field. In the decades following 1840, and especially after 1867 when Nitzsch's monograph was translated into English, other anatomists contributed pterylosis descriptions to the literature, most of them isolated studies of the general anatomy, including pterylosis, of new or difficult genera. Pterylosis was then considered of basic importance as a taxonomic character, and was used to help define orders and particularly to place passerine families in many of the classifications proposed in the latter half of the 19th century (e.g. Sharpe, 1891). At about the beginning of the 20th century pterylosis began to be neglected; it was used less often as a taxonomic character, and was gradually omitted from most general anatomical studies. This rejection was probably due to several factors. The entire field of anatomy declined as other aspects of ornithology became more popular. When the few remaining anatomists had occasion to reexamine some of the species studied by Nitzsch, they occasionally found errors in his descriptions. These inaccuracies were attributed to Nitzsch's use of dried study skins when fresh or alcoholic specimens were not available. Unfortunately the Pterylographie does not indicate which type of material was used for any given species description, leaving open the question of relative degree of accuracy. It also became apparent that although a large number of species had been described by Nitzsch and others, no study of the variability of pterylosis, vital to its evaluation as a taxonomic character, had yet been made. Several authors, from Lucas (1895) to Berger (1957), have called for a thorough study of the variation in some group of birds, particularly of a passerine family, in order to be better able to evaluate the accuracy