Meaning of Birdsong

The Meaning of Birdsong

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Ornithologists divide bird vocalizations into songs and calls. (Krebs and Kroodsma, 1980) A song has been defined as "loud and sustained vocalizations delivered seasonally by males in possession of a breeding or courting territory." (Nottebohm 1972). However, songs and calls are not so easily characterized. The functional roles of song may be played by calls in some species, sometimes females as well as males sing (European Robin), and song is not always restricted to the breeding season. (Red-winged blackbird) (White-throated Sparrow, personal observation)(Song Sparrow, personal observation). Although the vocalizations referred to as song tend to be structurally more complex than calls, there are many exceptions, for example, the song of Henslow's Sparrow consists of no more than a "hiccup" lasting less than one second. (Krebs and Kroodsma 1980).

Bird song, like music and speech, is structured in the sense that notes are acoustically distinct and tend to occur in a characteristic sequence (Lemon 1977; Marler & Peters, 1981). Birds may use the serial structure of conspecific song in the recognition process. (Ratcliffe & Weisman, 1986). Songs lacking introductory portions are rarely as stimulating as entire songs. (Ratcliffe & Weisman, 1986) and songs with inappropriate endings also reduce response levels. (Baker, 1983; Ficken & Ficken 1973). Sometimes the syntax of indivdiual ntoes or note elements is important for song recognition (Shiovitz & Lemon, 1980). Also, territorial neighbors often "match" each other's songs with the most similar sequences from their own repertoires (Falls, Krebs, & McGregor, 1982; Todt, 1975)

Most songs of passerine birds (songbirds) consist of a limited variety of arrangements of a fairly small number of sound types. These types include pure tones, frequency sweeps, trills and buzzes. (Richards, 1981) Songs can also be differentiated by the spacing between notes. (Richards, 1981) Grassland birds tend to have more rapid trills than the forest birds. This is attributed to the absence of the constraint of reverberation in grassland habitats. (Richards, 1981)

Similar species of birds often sing with similar song structure patterns. A very common structure is a pattern of one or a few clear and simple introductory notes followed by more rapid and complex notes or a trill. This pattern has been referred to as the "sign-on" phenomenon. Richards (1981), Shiovitz (1975) Richards found that a great many birds have narrow frequency, widely spaced introductory notes which are essentially pure tones without pronounced species-specific characteristics (though the notes are often of a fairly constant structure within a given species).

Song sparrow songs typically are composed of two to seven phrases of either identical trilled syllables or of note complexes, which are sequences of unrepeated notes (Kroodsma, 1977; Marler & Seaman, 1986; Mulligan, 1966). A note is defined as a continuous tracing on an audiospectrogram, and a syllable is a repeated (trilled) sequence of notes. Trills and note complexes usally alternate within a song. Sucn a comlex accoustic signal has the potential to convey diverse information pertaining to the vocalizer's species, dailectal and individual identities, and motivational state. Individuals have repertoires of two ormore more song types. (Krebs & Kroodsma, 1980; Nelson, 1987)

On Long Island, most song sparrow songs consist of a note-complex phrase of one to five (usually two) syllables followed by a trill consisting of 3 or more identical syllables uttered in rapid succession. A few songs lack either a note-complex or a trill phrase or have the note-complex phrase following the trill phrase. Most syllables are composed of several notes; and many syllables have a wide frequency range, particularly those in the trill phrase. Most males on Long Island have 2 to 6 song types, most of which are unique to that male. Approximately 27% (n= 166) of the individuals recorded shared one or more song types with other males (Ewert 1978). From Ewert, 1980 at 380.

The song of the eastern towhee typically consists of an introduction of 1 to 4 simple syllables followed by a trill. the introductory syllables are relatively tonal. the syllables ofthe triall ore usually broad frequency sweeps, repated at rates of between 4 and 40 syllables/sec, with a mean of about 11 syllables/sec. (Richards, 1980) The trill in the song ofthe towhee is clearly susceptible to degradation of long distances of 100 meters or more. The introductory syllables, on the other hand, aremuchless susceptib le to degradation.

Birds discriminate entire songs that typify different individuals or different geographic locales. (Nelson, 1987,

A single individual of a particular species of song bird probably sings more than one song. "In at least three-quarters of all the songbird species, each male sings in more than one variant of the species characteristic song." (Krebs and Kroodsma 1980). This collection of song variants, which may range in number from two to several thousands according to species, is referred to as the song repertoire of a male. (Krebs and Kroodsma 1980). Reportoire size is known to increase with age in some birds, including the mockingbird. (J. Baylis), canary (Nottebohn & Nottebohm, 1978) and red-winged blackbird. (Yasukawa, et al. 1980). Some birds use a different song in their repertoire in the center of the territory where the resident is very likely to attack an invader, and others at the edge of the territory. (Krebs & Kroodsma 1980).

Repertoires may be related to pressure in mate selection with females preferring males with larger repertoires. Repertoires play an important role as a territorial signal. Territorial songbirds of some species recognize the song of their neighbors and can discriminate between familiar and unfamiliar songs. (Krebs and Kroodsma, 1980) Individual recognition of voiceis also well established in the use of simple calls, for example, between parents and offspring. (Krebs and Kroodsma 1980) (Beer, 1970) Repertoires may play a role as "family badges allowing the recognition of classes of individuals of different degrees of relatedness. (Treisman, 1978).

A surprising number of birds incorporate elements mimicked from other species or from inanimate sounds in their song repertoires. Mimicry, meanign the copying of sounds other than species-specific vocalizations, is probably very widespread. there is a contuum from species which occasionally mimic the sounds of other birds to those with a repertoire constructed largely or entirely of mimicked sounds. [e.g. marsh warbler (Lemaire, 1975) (Krebs and Kroodsma 1980)]

Many species of birds have different local dialects. That is, bird vocalizations vary from one population to another. (Thielcke 1969, Lemon 1975, Baptista & King 1980, Krebs and Kroodsma, 1980). The song of a particular species of bird may sound different in different geographical regions. The variation may occur over a broad geographic area, in various regions of one continent, or between bird populations on islands and those on the nearby mainland. "Variation is most conspicuous when birds in one locality share a repertoire distinct from other localities." In other words, there can be local dialects. (Lemon 1966)

Birds use vocalizations to communicate a wide-variety of information. Vocalizations are used to hold a family flock together in the winter, to recognize members of the same species ...... the increasing tempo of the song seems to be critical for species recognition in the field sparrow. (Goldman 1973). The repetition of similar or identical syllables facilitates species recognition in the brown thrasher. The tempo of song may be one important cue in species recognition of the Rufous-sided Towhee. (Ewert 1980). Changing the time interval between syllables of normal song by as little as 0.05 s resulted in statistically significantly reduced responses to song by indigo buntings. (Emlen 1972) and common yellowthroats. (Wunderle 1978).

Song-matching occurs when a bird responds to playback or a rival with a song out of its repertoire that closely resembles the stimulus song. (Krebs & Kroodsma 1980).

Frequency shifting: Researches have used playback experiments to study the response of wild and captive birds to controlled recordings. One such study involved the patterns of response of captive black-capped chickadees to normal and altered versions of their species specific "fee bee" song. ((Ratcliffe & Weisman, 1986) The normal fee bee song of chickadees has a simple structure, consisting of two clearly whistled ntoes, the second slightly lower in freqency (by 0.4-0.5 kHz) than the first. ONly males sing ould fee bees, usually in the context of long-distance territorial advertisement (Ficken, Ficken & Witkin 1978) Males occasionally shift frequency of the fee note or omit the bee or add a second bee, but on the whole, songs of individuals are highly stereotpyed (Ficken, 1981; Ratcliffe & Weisman, 1985).

Previous researchers have used the level of aggressive response by the bird to playbacks as a measure of song recognition. Different species vary in their behavior to playbacks, and the systems of measurement used in various studies vary correspondingly. For birds that increase their rate of singing, the easiest measure is a count of the number of songs during the playback. this has been used, for example, in ovenbirds, in white-throated sparrows and in stripe backed wrens. For birds with a number of responses to playback (for instance flying, approaching, attacking, visually displaying), either the responses can be evaluated separately, or they can be combined into an overall score of intensity of behavior. (Richards, 1981)