- McGill University
Summary
The present paper examines how singing is used in territorial communication between neighboring male song sparrows, Melospiza melodia. We concentrate upon the "dynamics" of song behavior, in which shortterm variations in patterns of singing are analyzed from two perspectives. First, evidence is sought that neighbors interact with song, as opposed to their song patterning fluctuating randomly with respect to one another. Second, we investigate the behavioral correlates of song patterning; in particular, temporal changes in patterning are related to the probability that the singer will behave agonistically toward a neighbor. Song patterning consists of a complex of features which may vary as songs are produced over time. One temporal feature that is common to all song birds is the rate at which they sing. We will investigate whether neighboring song sparrows coordinate variations in song rate, and whether song rate tends to increase or decrease with the probability of aggressive conflict. Among species in which individuals sing repertoires of discrete song types, additional features are available for agonistic communication. Song sparrows, for example, have repertoires of five or more song types, but the sequence in which these songs are produced is not constant (MULLIGAN, 1966). Therefore neighbors can potentially interact by temporally associating (or possibly matching) particular song types, and different song types might be delivered with varying levels of aggression. Futhermore, song sparrows sing with "eventual versatility" (sensu HARTSHORNE, 1956), meaning that each song type is repeated a variable number of times before the singer switches to a new type of song. As with song rate, variations in the rate of switching song types may be coordinated between interacting singers, and may also represent different levels of agonistic stimulation. While all of these features can be described, this study will compare the relative degrees to which song sparrows utilize song rates and repertoire-dependent features in territorial communication.
Methodology
Six male song sparrows on contiguous territories were observed intensively from May to August, 1978, in an old field near the Queen's University Biological Station, Chaffey's Locks, Ontario. Subjects were captured in mist nets, marked on the tail with different colors of acrylic paint, and released. All subjects were mated, but only some nests were located throughout the two to three full breeding cycles which comprised the observation period (NICE, 1937), so data on reproductive status were not considered in the analyses. Observations were made at all times of day from sunrise to sunset. Territories were divided into quadrats with an area of 12 meters squared marked by numbered stakes. Stereophonic recordings were made of one or two birds at a time with a Uher 4200 tape recorder with two Uher microphones mounted on 75 cm parabolic reflectors. Along with recorded songs, the date, time of day, identity of singer(s), quadrats from which they sang and concurrent behaviors were noted. Information contained in tape recordings was transcribed onto paper in the laboratory. The intervals between the beginnings of successive songs of individual and counter singing g subjects were measured with a stop watch. Songs were identified by comparing field tapes played at 1/4 speed with a catalog tape that contained all the song types of each subject. Confidence in the supposition that complete repertoires were cataloged stems from the fact that only six subjects were recorded over three months. A Kay Electric Sonagraph at wide-band settings was used to verify identifications made by ear.