Structure of the feather
The habitat of the feather mites, as the name clearly indicates, is the plumage, mainly the large flight feathers (remiges and retrices) and with heavy infestation also the larger coverts and other plumage areas.
In order to clearly comprehend the pattern of living of the feather mites in the plumage it is necessary to briefly describe the feather structure as well as classifications of the respective plumage areas. We adhere closely to the work of Helmut Sick (1937) titled “Morphologisch-funktionelle Untersuchungen über die Feinstruktur der Vogelfeder” (“Morphologic-functional examinations of the fine structure of the bird feather”; J. für Ornithologie 85, H.2) as well as relevant orthological standard literature. Sick added the standard latin word, the most important German synonyms as well as the English names to the main classification.
The well developed contour feather consists of a shaft, the quill (=Scapus, Hauptkiel, quill, Fig. K) and the bilaterally attached feather vanes (Vexillum, vane, Fig. FF).
Fig. Draft of a contour feather (after Sick)
The quill consists of a short, proximal, unfeathered section, the calamus (fig. FR) and a long distal main end piece, the rachis (=Hauptschaft, shaft, fig. S). The two feather vanes consists of an inner and an outer vane. The feather vanes have a common periphery (=feather periphery), which is the outline of the entire feather or the edge of the feather (=edge of the feather vane, fig. Fr.), enclosing the entire feather surface. Everything that is located on the edge of the feather surface is outside and everything that is located against the quill is inside. The feather vanes are formed by the feather barbs (Rami, secondary quills, barbs, fig. Rm) with their radii (Radii, Fasern, Fiedern, barbules, fig. Pr. Dr), which are bilaterally attached to the ramus.
The fine structure of the radii is of no great importance for classifying the settlement areas of the feather mites and therefore we shall not go into detail here.
On the other hand the insertion of the rami on the shaft is very important for the feather mites as this area represents the main habitat. Quill mites are found mainly here and in the quill.
The rachis consists of a dorsal and a ventral ridge. The dorsal ridge points away from the bird (upper site) and the ventral ridge towards it (undersite). The rami insert bilaterally in a line, which is close to the dorsal ridge. The ventral ridge has a centrally located groove along the entire rachis. The groove ends in a little dimple (Umbilicus superior) at the end of the vane origin and the beginning of the quill. In this area a minor feather is located depending on the type of feather. This minor feather is usually not present in large plumage, which is of greater importance for observing feather mites.
Proximally the calamus ends with a round hole, the navel (Umbilicus inferior), which is connected with the papilla, the growth zone containing the pulpa (nutrition of the feather during the growth phase). With completion of the growth phase the pulpa is replaced by a fine membrane, the so-called “feather-soul”. In the region of the calamus the feather is surrounded by skin and is thereby embedded in the wing. The calamus is translucent and almost hollow. Membranous rests from the growth phase are still present. The rachis contains “little pulp caverns”, these are the so-called pulp cells- horn substances.
Arrangement and classification of the feathers
The remiges (flight feathers) are divided into secondaries (remiges secondariae) and primaries (remiges primariae) depending on the point of origin on the skeleton and are then numbered starting from the bend of the wing (wrist).
Fig. Insertion of the remiges. According to Van Tyne and Berger (1959) from Schildmacher: Introduction to Ornithology. Fischer, Jena, (1982).
The number of the primaries is relatively constant with 10, whereby individual bird species can also have 8, 11 or 12. The secondaries vary between 6 (humming bird) and 37 (albatros). Usually there are 17-18.