page_title: Glossary of bird terms
section_title: P
hierarchical_section_title: Glossary of bird terms / P
caption_attribution_description: Melopsittacus undulatus
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: passerine 
  Also, perching bird. Any bird of the order Passeriformes, which includes more than half of all bird species. A notable feature of passerines compared to other orders of Aves is the arrangement of their toes, three pointing forward and one back, which facilitates perching. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders, with over 5,000 identified species. The order has roughly twice as many species as Rodentia, the largest order of mammals. There are more than 110 families of passerine birds, the second-most of any tetrapods (after Squamata, the scaled reptiles).
  pectinate claw 
  A claw on the middle toe with a serrated edge. This edge may either be finely or coarsely serrated. It is used in preening, functioning similar to a comb. It may be used to straighten the rictal bristles of some birds or to remove parasites, although the latter, in a limited investigation, did not prove to be true.
  pennaceous feather 
  Also, contour feather. A type of feather present in most modern birds and in some other species of maniraptoriform dinosaurs. Pennaceous feathers have a stalk called a quill, with the basal part called a calamus, that is embedded in the skin exclusively at pterylae (feather tracts). The calamus is hollow and has pith formed from the dry remains of the feather pulp. The calamus stretches between two openings—at its base is the inferior umbilicus and at its distal end is the superior umbilicus; the rachis of the main stem, hosting the vanes, continues above it. The rachides of contour feathers have an umbilical groove on their underside, with the vanes or vexilli, spreading to either side. The vanes comprise many flattened barbs, that are connected to one another by hooklets that are anchored into flanges on proximal barbules on neighboring barbs. Some specialized feathers are considered "modified" contour feathers, such as ear coverts and bird eyelashes called rictal bristles. Contrast: plumulaceous (down) feathers and filoplumes.
  philopatry 
  The habit of a bird returning to the area it first bred.
  pigeon milk
  The term for crop milk when found among all pigeons and doves.
  pileum 
  As defined in the treatise Manual of Ornithology: Avian Structure and Function, the "entire top of the head, including the forehead, crown and occipital regions."
  pin feather 
  Also, blood feather. A developing feather encased in a feather sheath that, unlike a fully developed feather, has a blood supply flowing through it. As such, damage to pin feathers can cause significant bleeding. Pin feathers may be the first feather growth during a bird's infancy, or those growing during moulting at any stage of a bird's life. As pin feather growth progresses, the blood supply is concentrated only in the base of the calamus. Pin feathers begin to develop after the feather bud invaginates a cylinder of epidermal tissue around the base of the dermal papilla, forming the feather follicle. At the base of the feather follicle, epithelial cells proliferate to grow the epidermal collar or cylinder. As the epidermal cylinder extends through dermis, it differentiates into a protective peripheral sheath, longitudinal barb ridges and growth plates. Over time these barb ridges grow in a helical manner, branching to create barbs and barbules, and fusing to form the central feather shaft. Moreover, the barb plate further differentiates into hooklets and cilia, while the marginal and axial plate die to form the intervening space within the feather structure.
  pinioning 
  Also defined: pinion joint. The act of surgically removing one pinion joint—the joint of a bird's wing farthest from the body—thereby stopping the growth of the primary feathers, to prevent flight. The animal welfare impact of pinioning is subject to increasing debate. For example, it is known that the operation, which is often performed without pain relief, is just as painful in young birds as in mature birds, if not more so. Evidence also suggests that pinioning may cause a phantom limb syndrome
caption: A budgerigar with pin feathers showing.
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