Bird song in temperate zone passerines is a trait under sexual selection in males. Female song is still thought to be rare in this group. Here we show that female song is common in a temperate zone population of house wrens (Troglodytes aedon), and we provide evidence for its functional role in defending against male and female conspecifics. We observed that females sang most frequently at the onset of egg laying with song becoming less common as incubation approached. Thus, females sang most during the time when eggs were left unguarded and susceptible to conspecific attack. We also conducted playback experiments to test whether

No abstract

The majority of work on aggressive signaling has focused on male–male contests. Although females in many species compete over important resources, female signals are understudied. In house wrens (Troglodytes aedon), females compete with other females to protect nesting cavities and eggs. We suggest that a high‐pitched, low‐amplitude call, hereafter abbreviated as ‘HI’, may be an aggressive signal used by female house wrens. Using playback of simulated female intruders, we found that females used HI calls significantly more often during playback of female house wrens compared to playback of heterospecifics. Additionally, HI calls were given significantly more often in the minute preceding physical attack. In comparison, song rates did not predict future attacks. Finally, we present pilot data that suggest listening females may respond more aggressively to female playback containing HI calls compared to playback containing only songs. This suggests the reliability of HI calls could be maintained by a receiver retaliation rule. HI calls bear a striking resemblance to the low‐amplitude songs of many male songbirds, in terms of both acoustic structure and social context. This is one of the few reports of a putative low‐amplitude aggressive signal in a female songbird. However, the nature of female competition may make low‐amplitude signaling an underappreciated signaling form in female animals.