Deciphering the Function of Low-amplitude Songs: Courtship, Aggression, and Hormones

date January 17, 2014
comments no comments.

Friday, January 17, 2014 4:00 p.m. ETC 4.150

Dr. Dustin G. Reichard
Department of Evolution and Ecology
University of California, Davis

Across the animal kingdom, acoustic signals serve a variety of important functions in aggression, mate attraction, courtship, and alarm-related signaling. Previous research on the function of acoustic signals has focused predominantly on high-amplitude (loud), long-range songs (LRS), while largely ignoring the low-amplitude (quiet) songs produced during close-proximity, conspecific interactions. Low-amplitude songs can be divided into two classes: (1) soft, long-range songs (soft LRS), which do not differ structurally from a species’ LRS, and (2) short-range songs (SRS), which can be widely divergent from a species’ LRS in both spectral and temporal characteristics. During my dissertation, I focused on determining the function of low-amplitude songs in a North American songbird, the dark-eyed junco (Junco hyemalis). Male juncos produce a distinct soft LRS and SRS during the breeding season, and SRS is produced at two distinct tempos, slow and fast. I performed a series of experiments involving song playbacks and presentations of live, male and female conspecifics to free-living male juncos to determine the social contexts in which males produce low-amplitude songs and the behavioral and hormonal responses that different songs elicit. The results of these studies provide multiple lines of evidence suggesting that soft LRS may function in both male-male and male-female interactions, while slow SRS functions predominantly in male-female interactions associated with courtship. During simulated courtship interactions in the field, paired and unpaired males appeared to use distinct courtship strategies by differing substantially in LRS production, proximity to the female, and activity, but producing similar amounts of SRS and visual displays. Finally, a meta-analysis of North American breeding birds found that low-amplitude vocalizations are relatively common. Collectively, these results emphasize that future studies of acoustic signaling in any taxon should focus on all components of the acoustic repertoire including both high- and low-amplitude signals.