page_title: Glossary of bird terms
section_title: R
hierarchical_section_title: Glossary of bird terms / R
caption_attribution_description: English: Range map of Sylvia atricapilla, based on Baker, Kevin (1997) Warblers of Europe, Asia and North Africa (Helm Identification Guides), London: Helm, p.&#160;102 ISBN: 0-7136-3971-7. Mason, C F (1995) The Blackcap (Hamlyn Species Guides), London: Hamlyn, p.&#160;16 ISBN: 0600580067. Simms, Eric (1985) British Warblers (New Naturalist Series), London: Collins, p.&#160;68 ISBN: 0-00-219810-X. Base map is File:BlankMap-World-large.png
context_page_description: The following is a glossary of common English language terms used in the description of birds—warm-blooded vertebrates of the class Aves, characterized by feathers, the ability to fly in all but the approximately 60 extant species of flightless birds, toothless, beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart and a strong yet lightweight skeleton.
  Among other details such as size, proportions and shape, terms defining bird features developed and are used to describe features unique to the class—especially evolutionary adaptations that developed to aid flight. There are, for example, numerous terms describing the complex structural makeup of feathers; types of feathers; and their growth and loss.
  There are thousands of terms that are unique to the study of birds. This glossary makes no attempt to cover them all, concentrating on terms that might be found across descriptions of multiple bird species by bird enthusiasts and ornithologists. Though words that are not unique to birds are also covered, such as "back" or "belly", they are defined in relation to other unique features of external bird anatomy, sometimes called "topography".
context_section_description: rachis 
  Plural: rachises; rachides.  Also, shaft. Variable sp.: rhachis. Also defined: medulla. The distal or upper section of the quill, above the calamus, stretching from the superior umbilicus to the tip of the feather, upon which the vanes and other structures are anchored. The rachis is flexible from side to side toward the blade projections, but far stiffer inward and outward from the bird's body. This arrangement aids in allowing the flight feather to act as a "resilient airfoil". The rachis is composed of two layers: a pithy, opaque material makes up the core layer called the medulla, which is covered by a thin and translucent outer layer or cortex that features longitudinal internal ridges on the dorsal side and external ridges on the ventral side.
  rectrices 
  Singular: rectrix. From the Latin for 'helmsman', they are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the tail of a bird, which help it to brake and steer in flight. They lie in a single horizontal row on the rear margin of the anatomic tail. The vast majority of species having six pairs. They are absent in grebes and some ratites, and greatly reduced in size in penguins. Many grouse species have more than 12 rectrices. Some species (including ruffed grouse, hazel grouse and common snipe) have a number that varies among individuals. Domestic pigeons have a highly variable number, due to centuries of selective breeding.
  remiges 
  Singular: remex. Also defined: postpatagium. From the Latin for 'oarsman', they are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feathers on the wings of a bird. They are located on the posterior side of the wing. Ligaments attach the long calami firmly to the wing bones, and a thick, strong band of tendinous tissue known as the postpatagium helps to hold and support the remiges in place. Corresponding remiges on individual birds are symmetrical between the two wings, matching to a large extent in size and shape (except in the case of mutation or damage), though not necessarily in pattern. They are given different names depending on their position along the wing.
  remicle 
  Also, little remex. The most distal primary feather. The remicle is very small and usually non-functional—interpreted by Christian Ludwig Nitzsch as "an aborted first primary". It was named by Richard S. Wray in 1887, who similarly thought of it as "representing an originally functional primary".
  resident 
  Also, permanent resident; sedentary. Non-migratory; a bird that stays year-round and breeds in one geographic area or habitat. Both permanent resident and sedentary are common with the defined usage. Although resident is used in this sense, it is often used as well for birds that are "migratory in part of their breeding range and resident elsewhere", e.g., "Eurasian blackcaps (Sylvia atricapilla) are summer visitors to Eastern and Northern Europe, resident in Western Europe and winter visitors to Africa."
  rictal bristles 
  Also, bristles; bristle feathers; eyelashes. Stiff, hair-like, tapering feathers with a large rachis but few barbs found around the eyes and the base of the beak of some bird species. They are common among insectivorous birds, but are also found in some non-insectivorous species. They may serve a similar purpose to eyelashes and vibrissae in mammals. Although there is as yet no clear evidence, it has been suggested that rictal bristles have sensory functions and may help insectivorous birds to capture prey. There is some experimental evidence to suggest that bristles may prevent particles from striking the eyes if, for example, a prey item is missed or breaks apart upon contact.
  rosette 
  Also, gape rosette. A fleshy rosette found at the corners of the beaks of some birds, such as the puffin. In the puffin, this is grown as part of its display plumage.
  rhamphotheca
  The outer surface of the beak consisting of a thin horny sheath of keratin, which can be subdivided into the rhinotheca of the upper mandible and the gnathotheca of the lower mandible. This covering arises from 
caption:    Breeding summer visitor
      Resident year-round
     Winter visitor
  Range map for Eurasian blackcaps—corresponding to the example use of "resident" in its definition at the left
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