Glossary of Terms

  •     Abdomen: The flattish posterior region on the underside of the trunk, approximately from the posterior end of the sternum to the vent.
  •     Adult: A bird whose feathering does not change in aspect in subsequent plumage cycles (i.e., Definitive). Such an individual is normally capable of breeding, but the converse often does not hold true; birds of many species breed, some even more than once, before attaining Definitive feathering. In other cases, birds may not breed in the first year of acquiring Definitive plumage. Hence, breeding status itself is not a practicable criterion for adulthood. In case of possible ambiguity, define what you mean.
  •     Alar tract: All the feathering on the wing, including the remiges and their coverts on the upper and under sides but not the scapulohumeral tract, from which it is separated by the humeral apterium.
  •     Alternate plumage: The name of the second plumage when there are two plumages per plumage cycle. The first plumage (i.e., the Basic plumage) usually is a more complete molt, and usually results in a plumage that is less brightly/conspicuously colored than Alternate plumage. May be numbered first, second, etc. to designate changes in color and molt pattern until the Definitive stage is reached. Acquired by a Prealternate molt that usually replaces only body feathers, not remiges and rectrices.
  •     Altricial: The character of a young bird that is helpless when hatched and requires considerable rearing before it can leave the nest. Upon hatching, such a nestling is either naked or sparsely downy and its eyes are closed.
  •     Alular digit: The anterior digit of the wing, represented by a single short bone on the leading edge of the carpometacarpus. Formerly called pollex.
  •     Alular quills: Small, narrow, stiff contour feathers attached to the alular digit on the upper side of the Wrist. Collectively known as the alula or bastard wing.
  •     Amplitude: The maximum excursion of air pressure from ambient pressure in a cycle of a sound wave. An objective measurement of sound, it is not an equivalent for loudness (q.v.).
  •     Anisodactyl: The arrangement of the toes in which the hallux is behind, and the other three toes are in front, as in passerines.
  •     Annual reproductive success: A measure of the breeding output of a population sample in one season, calculated as either the number of broods reared divided by the number of breeding females in the population, or the number of young reared to nest-leaving divided by the number of females in the sample (specify). This should be clearly distinguished from lifetime reproductive success, the number of offspring of an individual surviving at a given time.
  •     Apterium (plural apteria): An area of the body without contour feathers, either bare or sparsely furnished with down feathers or semiplumes.
  •     Attenuation: The decrease in amplitude of a signal during its transmission from one place to another.
  •     Auriculars: A patch of feathers around the ear opening and often screening it. They may be of coarser texture than the adjacent contour feathers. Synonym—ear coverts.
  •     Back: The anterior two-thirds of the region on the upper side of the trunk between the base of the neck and the base of the tail.
  •     Basic plumage: The name of the plumage generally acquired by a complete molt in adults (usually near or after breeding), and by an incomplete molt in juveniles, into a “nonbreeding” plumage, but ~ exceptions. May be numbered first, second, etc., to designate changes in color and pattern until the Definitive state is reached. Acquired by a Prebasic molt. If the plumage cycle consists of a single generation, it is always Basic.
  •     Booted: The character of the horny covering of the tarsus in which it is smooth, without scales or plates.
  •     Boreal: Pertaining to cool or cold temperate regions of the northern hemisphere, the northern coniferous zone and taiga.
  •     Breast: The rounded, anterior region on the underside of the trunk, between the lower border of the jugulum and the approximate posterior end of the sternum.
  •     Breeding site fidelity: The tendency for a bird to breed at the same site consecutively.
  •     Bristle: A feather with a stiff, tapered rachis and barbs only along the proximal portion. “Semibristles” are intermediate between bristles and contour feathers, having a conspicuous rachis, barbs along the entire rachis but widely spaced near the tip. and barbules very small or absent on most of the barbs.
  •     Calls: Vocal displays; stereotyped sounds used in commun­ication. Generally, calls are short and simple whereas songs are long and complex, but the distinction is not exact. Also, calls may be produced by both sexes at any time while songs tend to be given only by males in the breeding season. A species typically has 5—20 calls.
  •     Canopy: The uppermost stratum of foliage in forest vegetation; formed by the crowns of the trees; subdivided into two or three levels in rain forests.
  •     Capital tract: The pteryla that extends over the top of the head from the base of the upper mandible posteriorly to the point where the head and neck join. It is bounded on each side by an imaginary line passing from the mandibular ramus to the angle of the jaw. May be subdivided into subordinate tracts.
  •     Caudal tract: All the feathers of the tail, including rectrices, the upper and under tail coverts, and any feathering on the uropygial gland.
  •     Chick: The life stage of a precocial young bird. i.e., well-covered with down, leaving the nest and able to feed itself.
  •     Chin: The area, usually feathered, in the fork on the underside of the bill. Synonym—interramal region.
  •     Commissure: The line along which the mandibles come together. The place on each side of the mouth where the mandibles come together is the “commissural point” (synonym—angle of the mouth).
  •     Communal singing: Interactive singing by members of a social group.
  •     Complete body molt: Replacement of all contour (body) feathers, but no flight feathers (remiges or rectrices).
  •     Complete molt: Replacement of all body and flight feathers.
  •     Continental shelf: The shallow, gradually sloping seabed around a continental margin, not usually deeper than 200 m and formed by submergence of part of the continent. Beyond it, the continental slope falls steeply toward the ocean bottom.
  •     Contour feather: A feather with closely-knit, flat vanes, forming the outer covering of the body; does not include the flight feathers (remiges and rectrices).
  •     Cooperative polyandry: A mating system in which a single female and group of males form a communal breeding unit in which all males have an opportunity for mating.
  •     Countersinging: “Counter-replies,” sometimes alternating and sometimes overlapping, of song by two or more individuals who are responding to each other.
  •     Coverts: Contour feathers that overlie or underlie the bases of the remiges and rectrices and cover the rest of the wing or tail: usually smaller than the flight feathers.
  •     Crown: The posterior, upper region of the head, behind an imaginary line joining the anterior corners of the eyes. Adjective = coronal.
  •     Crural tract: The feathering on the leg below the knee, separated from the femoral tract by a narrow apterium.
  •     Culmen: The ridge-line of the upper mandible, from the forehead to the tip of the bill.
  •     Cycle (Sound): A complete repetition of a waveform. (Reproduction) The period from courtship until the rearing of independent young (or reproductive failure).
  •     Decibel (dB): A unit used to compare the intensity of two sounds. The decibel scale is logarithmic. One decibel corresponds to an intensity ratio of approximately 1.26, three decibels to a ratio of approximately two, and ten decibels to a ratio of exactly ten. Measurements in dB should refer to the base against which they are calculated. In most cases, the reference unit is 20 micropascals (or equivalents), but it can be calculated differently.
  •     Definitive: Typically, “adult” plumage. The condition of a plumage such that it does not change further with age, i.e., plumages in the same stage of subsequent plumage cycles are identical. May be applied to Basic, Alternate, or Supplemental plumages.
  •     Degradation: The change in form of a sound as it travels from its source. It is caused by differential attenuation of sound of different frequencies, refraction of sound passing through volumes of air of different densities, reflection of sound off surfaces, and diffraction of sound passing through gaps and around barriers.
  •     Dialect: Microgeographic variation in a sound signal, resulting from imitation by members of a local population. Sharp boundaries between local dialects can often be identified, though boundaries may differ depending on the features considered in drawing those boundaries.
  •     Dispersal: The act or process by which individuals move from their place of birth to a place of (potential) breeding.
  •     Dispersion: The pattern of distribution of individuals within a population, as clumped or aggregated, uniform, or random. In statistics, the distribution or scatter of observation about the mean or central value.
  •     Dorsal tract: The pteryla that extends posteriorly from the capital tract to the upper tail coverts. Along the neck it is bordered on each side by a cervical apterium; along the trunk it is bordered on each side by a large lateral apterium. The dorsal tract is divisible into four regions: the “cervical region” from the head to the trunk; the narrow “interscapular region” extends posteriorly between the shoulder blades; the saddle-shaped dorsal region from the shoulder blades to a point approx­imately halfway to the tail; the broad “pelvic region,” between the hips, from the dorsal region to tail coverts.
  •     Down feather: A general term for a fluffy or lax feather in which the rachis is usually short or absent, at least shorter than the longest barb. Two major categories: “natal downs.”— (synonym = nestling downs; neossoptiles [1st natal down], mesoptile [2nd natal down]) on newly hatched birds of many species, and “definitive downs” (synonym = adult downs)—on immature and adult birds, beneath the contour feathers. “Down” may be applied either to individual feathers or to the plumage composed of them.
  •     Duetting: Overlapping bouts of vocal or nonvocal sounds by members of a mated pair or extended family group. The degree of precision in the contributions of the participants varies.
  •     Egg dumping: The laying of eggs by more than one female of usually the same species in one nest. Synonym = dump nesting.
  •     Eye-ring: A ring of feathers around the eye, often distinctively colored. To be distinguished from “orbital ring” (q.v.).
  •     Feather coat: The total complement of feathers on a bird at any given time, regardless of how many generations of feathers (plumages) combine to produce that appear­ance. For example, the feathering of many birds during the breeding season comprises both Basic and Alternate plumages.
  •     Female access polyandry: A mating system in which females do not defend resources essential to males, but through interactions among themselves, may limit access to males. The system most closely resembles an explosive breeding assemblage (Emlen and Oring 1977) in which the operational sex ratio may become skewed with an excess of females.
  •     Female (or harem) defense polygyny: A mating system in which individual males control access to multiple females directly, usually by virtue of female gregar­iousness.
  •     Femoral tract: A tract on the Outer surface of each thigh, from the knee (and hip) nearly to the vent.
  •     Filoplume: A slender, hair-like feather with a small tuft of barbs or barbules at the tip.
  •     Flank: The region on either side of the trunk dorsolateral to the abdomen.
  •     Fledge: The process of acquiring the feathers necessary for flight and ability to fly. When complete, the bird is fledged. Not synonymous with nest departure. Do not apply the term to the parental process of rearing young until they can fly.
  •     Fledging success: A measure of breeding output in a population sample, calculated as the fraction or percent of total eggs laid that produced young which leave the nest, including additional broods, if any. Equals “hatching success” (q.v.) times “nestling success” (q.v.). Contrast with “nest success” (q.v.).
  •     Fledgling: The life stage of an altricial bird from the time it leaves the nest until it becomes independent of its parents. The term is restricted to species in which the young do not leave the nest until they are fully feathered and ready to fly.
  •     Forehead: The anterior, upper region of the head, above the lores, that extends up and back from the bill to an imaginary line joining the anterior corners of the eyes. Adjective = frontal.
  •     Forest: A relatively large area of closely canopied trees, mainly above 5 m and typically above 20 in. A small stand of trees may be termed a grove.
  •     Fourier analysis: A technique for analyzing sounds in which a wave is sampled at some relatively high rate (at least 2.5x the highest frequency to be resolved), and the value of the wave at each of these points is assigned a specific digital value. Digitized information is then subjected to a Fourier analysis that provides a sound spectrum appearing as frequency on the X-axis and amplitude on the r-axis. Hence each sound spectrogram represents a temporal slice through the sound that gives a reasonably precise portrayal of frequency and amplitude for a given instant. The duration of that instant varies with the range of frequencies to be sampled.
  •     Frequency: The number of complete cycles of a periodic process occurring per unit time. A parameter for a sound wave, it is an objective measurement and thus not equivalent to pitch. Usually measured as a number of cycles/second = hertz (Hz). The fundamental is the lowest frequency of a harmonic series.
  •     Gonys: The ridge formed by the junction of the two rami of the lower mandible near its tip.
  •     Grassland: A major biotic community in temperate regions consisting of flat to rolling, treeless, grass-covered terrain. The climate is subject to abrupt seasonal changes, winters being cold to very cold; rainfall moderate to low.
  •     Gular region: A region on the underside of the head that continues from the chin to an imaginary line between the angles of the jaw.
  •     Habituation: Waning of response to a stimulus over time.
  •     Hallux: The first toe, usually directed backward and reduced, sometimes absent.
  •     Harmonics: Components of a periodic wave that are integral multiples of the lowest or fundamental, frequency, which is the first harmonic; the component whose frequency is twice that of the fundamental is the second harmonic and soon. Harmonics may be overtones, but overtones are not harmonics. The overtone frequency is derived from the fundamental but the mathematical relationship to the fundamental is not simple.
  •     Hatching success: A measure of breeding output in a population sample, calculated as the fraction or percent of the total number of eggs laid that hatched, including additional broods, if any. This should be distinguished from hatching rate, which is the fraction or percent of nests in an observed sample in which at least one egg hatched.
  •     Heterodactyl: The arrangement of the toes in which the third and fourth are in front, the first (hallux) and second behind, as in trogons.
  •     Home range: The total area that a bird occupies during the breeding season or during the non-breeding season, but excluding the area traversed on migration or dispersal. It may: (1) be the same as territory (q.v.), (2) be territory plus an outside area that the bird frequents for food or other needs, or (3) contain no territory.
  •     Immature: A general term for any young bird from the time it acquires Juvenile plumage until it acquires fully adult (i.e., Definitive) feathering. It does not connote sexual immaturity unless so specified because immatures of some species may be capable of breeding. Immature is synonymous with juvenile except that the latter connotes sexual immaturity.
  •     Inshore: A coastal zone arbitrarily defined as extending 5 kilometers out from the low water mark. Where there are islands or islets well in sight of the shore, all intervening water and the zone up to 5 km beyond them should be included as inshore, as should seas of depth less than 6 In.
  •     Intensity: The power delivered per unit area in a sound wave. Intensity is usually expressed in decibels (q.v.) relative to 1,012 watts per square meter, which is approximately the threshold of human hearing.
  •     Interspecific territoriality: The persistent aggressive behavior exhibited by a territory holder of one species, showing to it some, if not all of the reactions usually forthcoming in intraspecific encounters.
  •     Iris (plural irides): A thin membrane in the front of the eye which by its state of contraction determines the size of the aperture (pupil) in its center.
  •     Jugulum: The region on the underside of the neck from the posterior margin of the gular region to the trunk.
  •     Juvenile plumage: The first generation of true (pennaceous) contour feathers. The feathers are usually less closely-knit, and differently colored than those which will follow. Acquired by the Prejuvenile molt (i.e., replacement of natal down in species which have a downy plumage) and usually lost by the First Prebasic molt (but there are exceptions.
  •     Kilohertz (kHz): Unit of measurement for frequency of sound waves, 1,000 hertz, or 1,000 cycles per second.
  •     Lek: A communal display ground where males congregate for the sole purpose of attracting and courting females, and to which females come for mating. Synonym = arena. The term may also be applied to a communal prenuptial display on such an area, specifically one involving ritualized contests among competitors, often for the rise of symbolic sites.
  •     Littoral: (1) The shore of a lake to a depth of about 10 m, (2) The intertidal zones of the seashore, extended or alternatively employed for non-tidal waters, to include the underwater limit to which the more abundant attached plants can grow, sometimes to a depth of 3Gm or more, corresponding to light penetration. May thus overlap inshore zone at subsurface levels.
  •     Lobate: The character of a swimming foot with a series of lateral lobes on the toes, as in grebes. Sometimes the foot may be palmate, but the hallux may bear a lobe, as in diving ducks.
  •     Lore: The area between the eyelid and the eye-ring and the base of the upper part of the bill.
  •     Loudness: The perception of the strength of a sound. For sounds that differ only in amplitude, relative loudness is directly related to relative intensity, but for sounds that differ in frequency and temporal characters, loudness is complicated psychophysical phenomenon. It depends on characteristics not only of the stimulating wave form but also of the reaction properties of the mechanical receiving system (ear) and neurological analyses. The relative loudness of different sounds may be different for humans and various species of birds.
  •     Macrogeographic variation: Overrating over geographic distances sufficiently large that birds from those locations have minimal contact with each other; generally, on the order of hundreds or thousands of kilometers. May refer to features of the body, eggs, habits, or sounds.
  •     Major digit: The main digit of the wing, represented by the two phalanges in line with the carpometacarpus.
  •     Malar region: The region on the side of the head from the base of the lower part of the bill to the angle of the jaw; it is bounded above by the lore, orbital region, and the auricular region, and below by the edge of the lower jaw.
  •     Male dominance polygyny: A mating system in which mates or critical resources are not able to be economically mono­polized. Males compete for females by sorting Out positions of dominance and/or directly demonstrating quality through display.
  •     Mantle: When the back, scapulars and wing coverts together present an area of distinctive color.
  •     Mate: An individual with which another individual shares gametes. (A mate can be pair-bonded or not.)
  •     Mean: Average- equal to the sum of the observations divided by the number of observations (denoted as a statistic of a sample by x, and as a population parameter by µ; arithmetic mean).
  •     Mesoptile: Down feathers of the second down plumage in species that have one.
  •     Microgeographic variation: Variation on a small enough geographic scale that young birds may be expected to disperse from one place to another; generally, on the order of a few kilometers. Usually used in reference to vocalizations.
  •     Migration: The regular movement of an individual or group between geographically separate, seasonal ranges. Within a species, populations may vary in the extent of their migration, and within a population, individuals may vary likewise.
  •     Migratory restlessness: The unsettled behavior of birds immediately before they are due to depart on migration, also called premigratory restlessness or the original German term, “Zugunruhe.”
  •     Mimicry: The close resemblance of one organism (the mimic) to another (or to a natural object: the model) to deceive a third (the operator). May be applied to interspecific appearance or sound learning (q.v.).
  •     Minor digit: The posterior digit of the wing, represented by a single, small phalanx behind the proximal end of the basal phalanx of the main digit.
  •     Modulation: Any periodic change of frequency, amplitude, or phase of a sound wave.
  •     Molt: The regular loss of part or all of the feather coat and replacement of it by a generation of feathers or other integumentary derivatives, whether this includes all or only a portion of the bird. Molts are named in relation to the incoming plumage, i.e., Prebasic, Prealternate, etc. A molt may be limited in time, protracted, or even interrupted. It may also be either complete (i.e., renewing all tracts) or partial (i.e., renewing only some tracts).
  •     Molt-migration: A regular movement in certain species from the breeding ground to sheltered areas where the birds molt.
  •     Monogamy: A mating relationship in which a male or a female is mated to a single individual during the period of one reproductive cycle.
  •     Nape: The region on the upper part of the neck, from the posterior margin of the crown to the trunk.
  •     Natal down: The plumage of down feathers, sparse or abundant, that first clothes a nestling, either present at hatching or appearing within a few days. Birds of a few orders have two successive generations of natal downs. Lost by the Prejuvenile molt.
  •     Natal philopatry: The tendency of a mature bird to return to its site of hatching for its first breeding effort.
  •     Neossoptile (neoptile): Feathers of the first (usually only) downy plumage.
  •     Nest success: A measure of breeding output in a population sample, calculated as the fraction or percent of total nests that produced young to leave the nest, including additional broods, if any. Contrast with “fledging success” (q.v.).
  •     Nestling: The life stage of a young bird while it remains in the nest.
  •     Nomadic: The characteristic of a species whose individuals move irregularly from place to place in response to rainfall, drought, or the emergence of food.
  •     Non-native species: a species living outside its native distributional range, which has arrived there by human activity, either deliberate or accidental.
  •     Nonvocal sounds: Sounds produced by the bill, feet, or feathers, perhaps used for communication. Synonym = mechanical sounds.
  •     Notched: A character of a primary remex in which one or both vanes are incised toward the tip. Synonym = emarginate.
  •     Note: A single tone of definite pitch. The term is often used more broadly in reference to a single continuous trace on a sound spectrogram. Synonym = phone, figure. and element. If you use these terms, define them unambiguously.
  •     Occiput: The posterior portion of the crown (q.v.), usually not distinguished unless the feathering differs from that of adjacent regions. Adjective = occipital.
  •     Offshore: The coastal zone that extends from the limits of inshore waters to the edge of the continental shelf or continental slope.
  •     Operculum: A horny flap covering the nostril.
  •     Orbital ring: A ring of bare skin around the eye. To be distinguished from “eye-ring” (q.v.).
  •     Palmate: The character of the toes in which the anterior three are united by extensive webs, as in ducks and gulls. Synonym = webbed.
  •     Pamprodactyl: The arrangement of the toes in which all four are in front, the hallux being turned forward, as in swifts.
  •     Pelagic: The zone of the deep ocean, beyond the continental slope.
  •     Pennaceous: Feathers in which the barbs of each vane are parallel and interlocked to one another via interlocking barbules on adjacent barbs, i.e., typical body feathers.
  •     Phrase: A seemingly natural segment of a song, such as a sequence of similar syllables or a group of dissimilar notes bounded by either repeated syllables or by the beginning or ending of a song. Alternatively, the term may refer to the repeated unit (“syllable”) in a song. Define your usage of this term unambiguously.
  •     Pitch: The perception of the relative frequency of a sound, dependent on frequency, loudness, and intensity. For sounds with a fundamental frequency and harmonic series, pitch corresponds to a frequency (at least in humans), but for other sounds the perception of pitch is a complicated psychophysical process. Unlike frequency (q.v.). pitch can be modified by characteristics of the receiving system. The pitch of sounds may be perceived differently by humans and various species of birds, and even by different individuals within a species.
  •     Plumage: A single generation of feathers, resulting from a single molt. Plumages are named Natal, Juvenile, Basic, Alternate, and Supplemental. The total feathering worn by a bird (which one typically thinks of as its “plumage” is usually composed of multiple plumages and is referred to as the feather coat).
  •     Plumage cycle: The period in an “adult” bird that extends from a given plumage or molt to the next occurrence of the same plumage or molt. Lasts one year in most temperate-zone species but is shorter in some tropical and oceanic species, or longer than a year in a few species at various latitudes.
  •     Polyandry: A mating relationship in which one female is mated to two or more monogamous males during one reproductive cycle.
  •     Polygyny: A mating relationship in which one male is mated to two or more monogamous females whose repro­ductive cycles overlap.
  •     Polygyny-polyandry: A mating relationship in which both males and females are mated to two or more members of the opposite sex during a single reproductive cycle.
  •     Powder-down feather: A modified feather, usually with the structure of a down, that produces a fine, talc-like powder by the proliferation and keratinization of cells that surround the barbs in the feather germ. Such feathers in different species are either dispersed among ordinary downs and contour feathers or clustered in specific areas, “powder down patches.”
  •     Precocial: The opposite of altricial. Born with a heavy coat of down; mobile soon after hatching, requires little direct parental care.
  •     Prealternate molt: The molt that brings in the Alternate plumage, if any.
  •     Prebasic molt: The molt that brings in the Basic plumage, commonly taken as the starting point of a plumage cycle.
  •     Presupplemental molt: The molt that brings in the Supplemental plumage, if any; it may follow either a Basic or an Alternate plumage.
  •     Psilopaedic: Born naked (little or no down) (and the rest is drag).
  •     Pteryla (p1. pterylae): An area of the body bearing rows of contour feathers. Synonym = tract.
  •     Ptilopaedic: Born with a dense coat of down.
  •     Rapid double-clutch monogamy: A mating relationship in which a female lays two clutches in succession, one incubated by her mate and the other by herself.
  •     Rapid multiple-clutch: Polygamy. A mating relationship in which a female lays at least two clutches with different mates and the male fertilizes at least two clutches for different mates in rapid succession. Males and females incubate separate clutches.
  •     Raptorial: The character of the toes in which they are deeply cleft, with large, strong, sharply curved nails, as in hawks.
  •     Ransi (mandibular) (sing. ramus): The two halves of the lower mandible, separated by soft tissue near the base (commissure) but uniting anteriorly in the gonys.
  •     Rectrices (sing. rectrix): Flight feathers of the tail.
  •     Remiges (sing. remex): The long, stiff feathers that project posteriorly from the wings, anchored to the bones of the forelimb. Two main series: primary remiges (“primaries”) attach to the hand bones, secondary remiges (“secondaries”) attach to the ulna. True tertials (not inner secondaries), if any, attach to the humerus.
  •     Repertoire: The variety of sounds that an individual uses in communication. Often refers in a more restricted sense to the diversity of songs that an individual bird uses.
  •     Resident: The characteristic of a species or population that is basically non-migratory.
  •     Resource defense polyandry: A mating system in which individual females control access to males indirectly, by monopolizing critical resources.
  •     Resource defense polygyny: A mating system in which individual males control access to multiple females indirectly, by monopolizing critical resources.
  •     Reticulate: A character of the horny covering of the tarsus in which it is formed into small irregular plates.
  •     Rictus: The soft, fleshy, posterior portion of the tomium near the commissural point.
  •     Riparian woodland: A biotic community, mostly of deciduous trees, near streams or bottomlands where there is an adequate supply of subsurface water; especially prominent in the more arid sections of the southwestern United States.
  •     Rump: The posterior one-third of the region on the upper side of the trunk between the base of the neck and the base of the tail. Synonym = pelvic region.
  •     Savanna: The tropical and subtropical grassland biotic community, transitional between grassland or desert and rain forest, typically with drought-resistant vegetation dominated by grasses with scattered tall trees; tends to be semiarid with few or no wetlands and should be at least semi-natural and in sizeable tracts.
  •     Scapulohumeral tract: A narrow pteryla on the upper side of each shoulder, across the joint or Just distal to it.
  •     Scutellate: The character of the horny covering of the tarsus in which it is formed into more or less overlapping scales.
  •     Scutellate-booted: The character of the horny covering of the tarsus in which it has overlapping scales in front but is smooth behind.
  •     Scutellate-reticulate: The character of the horny covering of the tarsus in which it has overlapping scales in front and small irregular plates behind.
  •     Semi-altricial: The character of a young bird that is down-covered when hatched, unable to leave the nest for a few weeks, and is fed by its parents.
  •     Semipalmate: The character of the toes in which the anterior three are joined part way by a small webbing.
  •     Semiplume: A downy feather with a large rachis, i.e., longer than the longest barb. Structurally intermediate between contour feather and down feather.
  •     Semi-precocial: The character of a young bird that is down-covered when hatched, leaves the nest soon afterward and moves a short distance away, while still fed by its parents.
  •     Serrate: The property of having a saw-like edge, either on the tomia of the bill or the horny covering of the tarsus.
  •     Song: A vocalization in which one or more sounds are consistently repeated in a specific and often complex pattern. It is usually uttered from conspicuous perches, most frequently by males (at least in temperate regions) during the breeding season. The foregoing definition is subject to exceptions. Song is believed to serve in attracting/stimulating a mate and in defending territory, but those functions should not be assumed without solid evidence.
  •     Sonogram: The general term for a graph of sound frequency against time, with intensity indicated by the darkness of the graph. Do not confuse with “Sonagram,” a graph of this type produced specifically on the Sona-graph Instrument (Kay Elemetrics Co.). Also, avoid applying this term to sound spectrograms of other variables, such as those made by fast Fourier analysis.
  •     Sound learning (sound imitation): An adaptive change in sound-making behavior that results from experience. It is often a two-stage process in which an animal first memorizes a sound and later produces good copies of that original. A bird may learn to recognize a neighbor’s vocalizations and yet not vocalize those sounds; this is not “sound learning.” Be sure to use “sound learning” or “vocal learning” in an unambiguous way.
  •     Sound spectrograms: A graph produced by any process that resolves sound in such a way as to show at what frequencies energy is distributed. With frequency on the X-axis, the Y-axis may be either time, as in a sonogram, or amplitude, as in a Fourier transformation. Synonym audio spectrogram.
  •     Sparse vegetation: Used of plants spaced more than twice as far apart as their diameter, distinguished from “open vegetation,” where the plants are on average separated by less than their diameter, and “closed vegetation,” where they are in contact or overlap. These terms relate to whichever layer of vegetation shows the most complete coverage.
  •     Subsong: Earliest “motor” stage of song development, during which a young bird is beginning to utter sounds that will eventually become adult songs.
  •     Supercillary: A horizontal stripe of distinctively colored plumage on the side of the head above the eye.
  •     Supplemental plumage: The name of any plumage that occurs in a plumage cycle in addition to the Basic and Alternate plumages (i.e., it is not homologous to either Basic or Alternate plumage). It may precede or follow the Alternate plumage. Acquired by a Presupplemental molt.
  •     Syndactyl: The arrangement of the toes in which the third (middle) and fourth (outer) are partly united with a single broad sole. as in kingfishers.
  •     Syllable: A repeated unit in a song. If using this term, define it unambiguously.
  •     Taiga: Northern, dense, predominantly coniferous forest, little disturbed or dissected and often containing swampy areas. Occupies the broad belt south of the tundra in upper mid-latitudes.
  •     Territory: A space within which an individual is aggressive toward, and usually dominant over, certain categories of intruders. May be roughly classified as either breeding or nonbreeding territory, with several types in each (Pettingill 1985: 259). Not to be confused with “home range” (q.v.).
  •     Tibiotarsal joint: The backward-pointing joint in the leg between the tibiotarsus (tibia) and the tarsometatarsus (tarsus). It is not the knee, the joint between the femur and the tibiotarsus, which is usually concealed by the feathering and musculature of the thigh. Synonym = intertarsal joint, ankle.
  •     Tomium: The cutting edge of the upper or lower mandible.
  •     Tonal quality: What distinguishes one sound from another of the same frequency. Physically, tonal quality is determined by the presence or absence of harmonics and their relative intensity and distribution, by transients, and by the rate and range of frequency and/ or amplitude modulation. Synonym = timbre.
  •     Totipalmate: The character of the toes in which all four are united by large webs, as in cormorants.
  •     Tundra: A major biotic community characterized by lack of trees: short, cool summers; permafrost below a surface layer subject to summer melt. Dominant plants: lichens, mosses, sedges, grasses, and low shrubs. “Arctic tundra” occupies the arctic region. i.e., north of the 100 C isotherm, where the mean temperature of the warmest month falls below that value and tree growth is not possible. “Alpine tundra” is above the tree line of high mountains (approx. 3050 m. in Rocky Mts. and Sierra Nevada-Cascade system).
  •     Variety: The sequential presentation of song types in a repertoire. If successive songs in a performance are of different types, a bird is said to sing with “immediate variety;” if a bird repeats one song type many times before switching to another song type, the bird is said to sing with “eventual variety.”
  •     Ventral tract: The pteryla on the underside of the body, from the junction of the mandibular rami to the circlet of feathers around the vent. In different species it may enclose a midventral apterium or be more or less divisible into such tracts as the cervical, pectoral, sternal, and abdominal.
  •     Vertical displacement: The characteristic of a species or population whose individuals regularly shift their altitudinal range in mountains. Synonym = altitudinal migration.
  •     Vocal convergence: The tendency for two or more birds to converge on similar vocal signals, usually as a result of vocal learning.
  •     Vocalization: Inclusive term for all avian sounds produced by the syrinx, in contrast to “non-vocal sounds” (q.v.).
  •     Whistle: A sound that most nearly approaches a pure tone, i.e., with a fundamental and no overtones.
  •     Woodland: An open stand of trees, usually below 15 m tall, too widely spaced to form a continuous canopy, and with an intervening growth of grasses or shrubs.
  •     Zygodactyl: The arrangement of the toes in which the second and third are in front, the first (hallux) and fourth are behind, as in woodpeckers.

Guidelines