A complex call of the black-capped chickadee (Parus atricapillus). I. Microgeographic variation

-We studied the syllabic structure of the Gargle, a complex vocalization of the Black-capped Chickadee that is often associated with agression, at three main sites in southeastern Wisconsin, at one site over an 11-yr period. Sites as close as 5.7 km showed major differences in syllables, and birds at some sites differed somewhat in the number of syllables per call. Each individual probably uses all the syllables (16-23 different ones) occurring at a particular site. The syllables occurring at the end of the vocalization were shared among different demes, while the introductory syllables were usually different. Syllables showed relatively little change with time. Dialects apparently correspond to demes in this species. The syllables are arranged in many combinations and permutations to generate a large variety of Gargle types, most of which are very rare. A few Gargle types are more common ("universals") and are usually confined to a particular site. Such a complex dialect pattern is unusual in a call. Received 27 April 1983, accepted 5 December 1983. SONG dialects have been much studied, and the picture that emerges is one of considerable variability among species (for review, see Mundinger 1982). No general rules apply to all species about the nature of the dialect variation, size of dialect groups, stability of dialects with time, or the correspondence of dialect groups to demes. Certainly, detailed studies are needed of a variety of avian species. Although song dialects occur and have been studied in many species, few researchers have dealt with nonsong vocalizations, i.e. those not involved with the dual role of territorial advertisement and pair formation. The exceptions are Thielke's study of Chaffinch vocalizations (Fringilla coelebs), Bertram's (1970) work with mynahs (Gracula religiosa), and Adkisson's (1981) work with Pine Grosbeaks (Pinicola enucleator). We investigated the microgeographic distribution of the Gargle, a vocalization of the Blackcapped Chickadee (Parus atricapillus), at five sites in southeastern Wisconsin, at one site for an 11-yr period. We were concerned with the following questions. (1) What is the syllabic composition of this call in different areas? (2) Does this pattern correspond to dialects? (3) Is there any evidence that dialects correspond to demes? (4) How is information about the identity of the individual, population, and species coded? (5) What is the pattern of transmission from generation to generation? Elsewhere, we examine individual repertoires, the functional significance of Gargles, and the possible selection pressures affecting Gargle dialects (Ficken et al. in prep.). Black-capped Chickadees are highly social, relying strongly on vocal signals (Ficken et al. 1978). Two vocalizations are especially complex: the commonly uttered Chick-a-dee, which has flock-specific characteristics (Mammen and Nowicki 1981), and the Gargle, a sputtery, explosive-sounding vocalization, which occurs year round, primarily in agonistic situations (Ficken et al. 1978). Gargles have several songlike properties: they have much greater syllabic complexity than the whistled "Fee Bee" (usually considered the "song" in this species) and are given primarily by males (Ficken 1981). Gargles often occur when males from adjacent territories engage in boundary conflicts, but they are not used in territorial advertisement. These calls also often precede copulation (Ficken et al. 1978). In the nonbreeding season, Gargles are usually associated with agonistic encounters, often when one bird directly faces or supplants another. In these contexts Gargles are a potent threat display, affecting access to food at feeders (Wipf 1981). Gargles are most often given singly, but, if the opponent does not leave immediately, a few additional ones may be given. An understanding of the social behavior and population ecology of the chickadee is necessary for an interpretation of their vocalizations. 349 The Auk 101: 349-360. April 1984 This content downloaded from 207.46.13.64 on Sat, 03 Sep 2016 04:23:18 UTC All use subject to http://about.jstor.org/terms 350 FICKEN AND WEISE [Auk, Vol. 101 The following is a brief summary of certain relevant aspects of the life history of the nonmigratory populations we studied in southern Wisconsin. Chickadees live in small flocks comprised of 4-8 individuals, including adults and juveniles of both sexes, for most of the year (late July to April). A flock is not necessarily permanent in composition, as some birds may leave or join. Certain individuals, however, tend to remain in association (Odum 1942). Pair formation occurs within the winter flock (Ficken et al. 1981). In spring (March-April), the flock gradually disrupts, pairs spending more and more time each day on their territories near or on the winter flock range (Odum 1942; pers. obs.). The young fledge in mid-June, stay with their parents for several weeks after fledging, and then disperse, mainly in early July, moving 0.24-11 km (median 1.1 km) from their birth places in our study area in Wisconsin (Weise and Meyer 1979). Following dispersal, young chickadees join flocks in their new area and are very likely to remain there permanently (Weise and Meyer 1979). Thus, the flocks formed in late summer consist of the resident adults of the area and juveniles that have dispersed to that area. Many chickadees live to be 2-5 yr old, and some very few survive 7-10 yr. MATERIALS AND METHODS We recorded vocalizations at five feeders in Ozaukee County, Wisconsin. Three are at the University of Wisconsin-Milwaukee Field Station, a site described by Weise and Meyer (1979). Two of these feeders (F9 and A8) are at the edge of Cedarburg Bog, where the predominant vegetation is white cedar (Thuja occidentalis) and tamarack (Larix laricina). The third (D7) is in a small swamp-hardwood forest at the edge of a large beech (Fagus grandifolia) and sugar maple (Acer saccharum) forest. The Field Station and adjacent areas of Cedarburg Bog that we studied comprise 440 ha, which support 250-325 chickadees. Each year about 200 chickadees frequent the six feeders in the area, which are stocked with sunflower seeds and suet from mid-November through April. We selected three feeders that were among those most distant from one another and supported a moderate number of birds. The birds using each feeder came daily from distances of up to 1 km or more. Each feeder had two perches 15 cm apart at the entrance. Although two chickadees frequently perched on the feeder at once, only one at a time would enter to feed. Agonistic interactions were frequent. Recordings were made from November to April each year. TABLE 1. Number of recordings of Gargles by year and site. Field Station RiverGrafYear D7 F9 A8 edge ton 197-0-1974 251 0 0 0