The Form and Function of Song in Female Song Sparrows

Abstract

We report on the occurrence and context of female song in the color-marked Song Sparrow (Melospiza melodia) population resident on Mandarte Island, British Columbia. Sonograms of three females showed that the structure of female song varied, but was usually less complex than that of males. At least one female's song was within the male range of complexity and could have been mistaken for a male song had the sex of the bird been unknown. Another female sang at least two distinct song types. Further, the songs of females recorded on Mandarte were similar to those recorded elsewhere from wild females and from captive females implanted with testosterone. Overall, singing by females on Mandarte was rare; only 12 of approximately 140 females were heard singing during 267 female-years of intensive observation. With one exception, female song was heard only from late February to mid-April, the period just prior to nest building when territory turnover and settlement by yearlings is most common. Most females (83%) sang during territorial conflicts between female intruders and female territory owners. Female song was more common when population density was high, average breeding success was depressed, and variation in breeding success was increased. We suggest that song results from elevated levels of testosterone in females that are engaged in intrasexual aggression, and we discuss some implications of female song for hypotheses of song learning.