DOES POPULATION DENSITY AFFECT THE SINGING BEHAVIOR OF FEMALE CANYON WRENS (CATHERPES MEXICANUS)?

Bird song has historically been considered from the perspective of temperate males despite females in many bird species being prolific singers. In this study, I investigated one species with female song, the canyon wren (Catherpes mexicanus). Canyon wrens do not duet like many other species with female song or other wrens. Instead, males and females sing sex-specific songs. The resource defense function of male canyon wren song is well-described, and males sing often during the breeding season. Females have only been observed to sing sporadically during the breeding season but sing reliably and often when exposed to playback of other females. Therefore, I hypothesized that females in higher breeding density areas would sing more and be more aggressive than those in lower breeding density areas, and females with closer distances between neighbors would sing more and be more aggressive than those with farther neighbors. I conducted this study over the course of two field seasons in two regions: southeastern Arizona (high density) and northcentral Colorado (low density). I spot-mapped breeding pairs in both areas, observed unprompted levels of song from females, and conducted playback experiments on females. I measured several behavioral parameters and song spectral parameters. I found that individuals in Arizona had significantly lower 95% frequencies in their songs, but did not find any other significant relationships between behavioral or spectral parameters and nearest neighbor distance, suggesting that other variables such as age, body size, breeding status, time of year, or genetic drift may better explain the variation in female songs between populations in Arizona vs. Colorado