The presence and microstructure of down compartments of feathers in representatives of nineteen orders of birds (Aves)

An inventory and description of the occurrence of the first studied down structures of feathers: combined barbs with typical down barbules and combined barbs with modified down barbules are carried out. The occurrence and distribution of these structures, as well as additional feather and umbilical barbs in different plumage pterylia of 441 birds of 129 species belonging to 19 orders were noted; 3330 feathers have been studied. Downy structures in the orders Charadriiformes and Passeriformes have been studied in most details. In the order Charadriiformes the families and their constituent species differ in the presence or absence of modified barbules. In the feathers of representatives of the order Passeriformes an additional feather/umbilical barbs and modified barbules do not occur in one of the same feathers. In the plumage of representatives of all studied taxa combined barbs with typical down barbules were found, which are present to a greater extent in the cover feathers, and to a lesser extent, on the flight and tail feathers. Combined barbs with modified down barbules are not so widespread in the plumage of the studied taxa and they are present only on the cover feathers. Among the studied orders the additional feather and umbilical barbs are absent in the plumage of Coraciiformes and Upupiformes. The adaptive and diagnostic significance of the studied downy structures is noted. The main function of all downy structures is thermal insulation, while maintaining the rigidity of plumage, preventing its sticking and sealing can be called secondary. The presence in some groups of birds on one and the same feather of an additional feather/umbilical barbs and modified barbules, as well as their various combinations, can be used as a taxonomic sign in combination with other ptylological characters. The presence of downy formations, their shape, structure, size and other features may indicate pterylia within some taxonomic groups of feathers. Along with visual inspection of feathers, light and electron microscopy was also used.