Song measure averages of allopatric and sympatric Black-capped and Mountain Chickadee individuals

Character displacement theory predicts that closely related co-occurring species should diverge in relevant traits to reduce costly interspecific interactions such as competition or hybridization. While many studies document character shifts in sympatry, few provide corresponding evidence that these shifts are driven by the costs of co-occurrence. Black-capped (Poecile atricapillus) and Mountain Chickadees (P. gambeli) are closely related, ecologically similar, and broadly distributed songbirds with both allopatric and sympatric populations. In sympatry, both species appear to suffer the costs of their co-occurrence: 1) both species are in worse body condition compared to allopatry and 2) hybridization sometimes yields sterile offspring. Here, we explored character displacement in the songs of Black-capped and Mountain Chickadees by characterizing variation in male songs from sympatric and allopatric populations. We found that Mountain Chickadees sing differently in sympatry versus allo..., Field sampling
During April and May of 2020, we recorded breeding Black-capped and Mountain Chickadees in both sympatry and allopatry. We recorded sympatric populations in Boulder County, Colorado, an area where hybridization is known to occur and we sampled along both species’ elevational distributions (Black-capped Chickadee n = 21; Mountain Chickadee n = 11). We recorded allopatric Black-capped Chickadees in Ithaca, New York (n = 21), and allopatric Mountain Chickadees near Truckee, California (n = 20). In both allopatric populations, neither species overlaps with any other Chickadee species. To avoid repeat sampling, we walked at least 500 meters between recordings and never sampled in the same location twice. We collected a total of 2,080 songs and an average of 29 songs per individual. All individuals produced a minimum of six songs. We recorded songs with a PMD660 or PMD661 Marantz digital recorder and a Sennheiser ME-66 unidirectional microphone with a sampling rate of 44,100 Hz..., , # **Song measure averages of allopatric and sympatric Black-capped and Mountain Chickadee individuals**

[https://doi.org/10.5061/dryad.3bk3j9kts](https://doi.org/10.5061/dryad.3bk3j9kts)

This data contains the averages of 14 song measures per 72 Mountain and Black-capped Chickadee individuals, in addition to the number of songs each individual sang and whether they came from a sympatric or allopatric population. We ran a principal component analysis (PCA) to assess if songs cluster by population using individual averages for all song measures. To assess which song measures explained the most variation between and within populations, we ran linear models for each PC axis with a loading stronger than 0.3, with the population as the dependent variable. Then, to assess variation between populations, we ran analyses of variance (ANOVAs) on each linear model followed by a Tukey HSD test to quantify differences between populations. We found that sympatric Mountain Chickadees sing a higher no...