The Non-Song Vocal Repertoire of the White-Crowned Sparrow

Abstract

We investigated the non-song vocal repertoire of the White-crowned Sparrow (Zonotrichia leucophrys) during the breeding season of 1981. Nine distinct vocalizations were recorded from males. Females used five of these; no calls were recorded exclusively from females. This limited sexual dimorphism in repertoire suggests that both vocal and non-vocal cues may be used in sex recognition. Most calls occurred in a variety of situations and appeared to convey only generalized behavioral messages. The structure of those calls whose information content seemed clear conformed to the predictions of models of selection pressures determining the physical forms of both longand short-distance animal vocalizations. Several authors have proposed explanations for the size, information content, and structure of display repertoires of social vertebrates. Smith (1969a) and Moynihan (1970) independently concluded that most species possess relatively small repertoires, usually around 4045 displays. Smith argued that this limit imposes generality on the information carried by displays, with the result that most are used in a variety of behavioral situations. Vocalizations comprise a major portion of avian display repertoires (Wilson 1975). According to Smith's (1969a) prediction, most of these calls should be used in a variety of situations. A number of studies support this prediction. The Eastern Phoebe (Sayornis phoebe) uses eight calls, three of which are common and used in many contexts (Smith 1969b). Ficken et al. (1978) found that many of the 13 vocalizations of the Black-capped Chickadee (Parus atricapillus) are used in a variety of contexts. Most of the 13 non-song vocalizations of the Ovenbird (Seiurus aurocapillus) are used in a variety of situations (Lein 1980). Both Ficken et al. (1978) and Lein (1980) found considerable sexual dimorphism in vocal repertoires of the monomorphic passerines they studied. Lein hypothesized that sexually-dimorphic vocalizations may assist in sex recognition in species which are monomorphic in appearance. Several workers have proposed that the physical structure of vocalizations is not arbitrary. Calls that carry messages to be conveyed long distances are thought to be subject to selection pressures imposed by physical laws of sound transmission (Marler 1959). The information content of some long-distance calls is most efficiently used if the call is localizable. Such calls should have a wide frequency range with many changes in frequency or repeated interruptions of the sound. Other long-distance calls carry information which is best used if the call is not localizable (e.g., alarm calls). These calls should have a narrow and intermediate frequency and should lack sudden changes in frequency (Marler 1959). In contrast, calls that convey information which is valuable only over short distances should be influenced by a relationship between motivation of the sender and structure of the call (Morton 1977). These motivation-structural rules (M.-S. rules) state that aggressive calls should be harsh, abrupt, and of low frequency. Calls least indicative of hostility should be pure tone-like, and of higher frequency (Morton 1977). To test the generality of these ideas, we conducted a message-meaning analysis of the vocal repertoire of a monomorphic emberizine, the White-crowned Sparrow (Zonotrichia leucophrys). These birds were chosen for the study because a color-banded population was locally available. The specific questions asked were: (1) How large is the vocal repertoire? (2) Are most calls used in a variety of behavioral contexts? (3) Does the repertoire show sexual dimorphism? (4) Are the structures of longand short-distance vocalizations consistent with those predicted? This lexicon of non-song vocalizations also complements the extensive literature on singing behavior in Whitecrowned Sparrows (reviews in Baptista 1977, Baptista and King 1980).