Song Frequency does not Reflect Difference in Body Size among Males in Two Oscine Species

Previous research has shown a negative relationship between body size and frequency among songbirds, but little research has been done within species. The purpose of this study was to evaluate whether body size had an effect on song frequency in the dark-eyed junco and the serin, two oscine species. The researchers also investigated the relationship between receivers’ sampling abilities and their accuracy in assessing body size of signalers. Researchers chose to study the dark-eyed junco and the serin in an attempt to establish this relationship because of their differences in song organization and repertoire size. To carry out this study, researchers recorded adult male calls 83 dark-eyed juncos and 41 serins in California and Portugal, respectively. After recording each call, the birds were caught, a variety of measurements were taken to determine body size and mass was also recorded. Songs were then analyzed using Avisoft SASLAB and frequency of each syllable of each song was recorded. This data could then be used to determine the peak, minimum, and maximum frequencies of each call. They also separated the juncos based on the number of syllable types that were expressed by the bird, ranging from one to five different syllables. The serins were analyzed as one group because they each expressed a variety of syllable types. Researchers then analyzed the relationship between frequency and body size or mass for each species as related to syllable type. In the case of both dark-eyed juncos and serins, researchers found that there was no relationship between frequency and body mass or size. Researchers also compared syllable types that were common in all male dark-eyed juncos and found that maximum frequency was positively correlated to body size. This result was unexpected based on previous research. Researchers hypothesized that there was no relationship because of the diversity of syllable types, the capability of oscines to produce a wide range of sounds, and the small differences in mass and body size between conspecifics.

In class we discussed the possible constraints on signal production, including body size as related to frequency. It was presented that as body size increased, frequency decreased in birds. However, in the case of the dark-eyed junco and the serine, there was no relationship between body size and frequency production, indicating that this general trend may not always be the case, especially in oscine species.