Dawn Chorus Male Song Patterns in Relation to Ancestry in the Black-capped Chickadee × Carolina Chickadee Hybrid Zone

Signals used in mate choice and intermale competition can deliver important information about the genetic quality of the sender, often serving as prezygotic barriers to hybridization. Our research aims to assess the extent to which song, as an acoustic mating signal, can reliably indicate a male’s ancestry, as well as the ways in which signal learning can become muddled in hybrid zones. I analyzed data from 2016 – 2019 involving Poecile atricapillus (Black-capped Chickadee) and P. carolinensis (Carolina Chickadee) and their hybrids at Hawk Mountain, Pennsylvania. Species-diagnostic SNP genotypes provided information about ancestry for each male, while autonomous acoustic recording units yielded samples of dawn chorus male repertoires mostly prior to incubation. The sample of males (N = 20) comprised 10% Black-capped Chickadees, 50% Carolina Chickadees, and 40% hybrids. Repertoires ranged from only Black-capped Chickadee songs to a mixture of Black-capped and Carolina chickadee songs, sometimes including new, unique hybrid songs that did not fall under either category; no observed repertoires comprised solely Carolina Chickadee songs. Song patterns did not actively reflect genetic identity in the hybrid zone: dawn song repertoire characteristics, in both song participation and repertoire composition, did not correlate with the proportion of Carolina Chickadee alleles. This supports previous studies involving acoustic signaling in this chickadee hybrid zone, which have found that the genetic introgression of Carolina Chickadee alleles in the population does not coincide with a simultaneous cultural change in song repertoires towards Carolina Chickadee songs. Instead, Black-capped Chickadee songs can dominate the acoustic culture for years, even after Carolina Chickadee alleles become predominant as the hybrid zone moves northward. These findings support the hypothesis that learning environment and neural template, more so than ancestry alone, shapes song repertoires of individual chickadees, which could affect mating patterns and hybridization dynamics.