Black-capped and mountain chickadee hybridization and breeding ecology in Boulder County, CO

Here, we combine three years of population monitoring with 569 whole
genomes to characterize the reproductive ecology of, and hybridization
between, two common songbirds, black-capped (Poecile atricapillus) and
mountain (P. gambeli) chickadees, for which hybridization is correlated
with human habitat disturbance across North America. Working within a
geographic region that we previously identified as a hotspot of
contemporary chickadee hybridization, we find that, despite geographic and
temporal breeding overlap, few early generation hybrids are produced,
indicating that reproductive barriers typically prevent contemporary
hybridization. Yet, every chickadee we sampled in sympatry possessed
heterospecific ancestry, indicating that both contemporary and historical
hybridization have occurred during the evolutionary history of chickadees
in Colorado. Why contemporary hybridization continues to occur despite
evidence for character displacement of chickadee song remains less clear,
but urban forests may play a role. This dataset includes: reproductive
information and genomic information for Colorado chickadees, as well as
simulation data for assigning wild birds to genomic classes (i.e.,
characterizing hybridization).