Novel hybrid finds a peri-urban niche: Allen’s Hummingbirds in southern California

Species range expansions and contractions can have ecological and genetic
consequences, and thus are important areas of study for conservation.
Hybridization and introgression are not uncommon in closely related
populations that experience secondary contact during a range expansion.
Allen’s Hummingbird (Selasphorus sasin) in California comprises two
subspecies: the migratory S. s. sasin, which winters in central Mexico and
breeds in central and northern California, and the resident S. s.
sedentarius, which lives and breeds year-round on several of the Channel
Islands off the California coast. Within recent decades, Allen’s
Hummingbirds have been found living and breeding year-round in the
southern California peri-urban mainland near Los Angeles. Ornithologists
assumed that the L.A. birds were an expansion of the island subspecies, S.
s. sedentarius due to similar but very subtle morphological
characteristics. However, the genetic relationships among the three
putative populations of Allen's hummingbird—migratory, southern
California mainland, and island—are unknown. We investigated these
relationships by analyzing variation of single nucleotide polymorphisms
from the three geographic regions where S. sasin are present. Our
population genomic analyses indicate that S. sasin hummingbirds inhabiting
mainland southern California are a hybrid population resulting from
admixture between S. s. sasin and S. s. sedentarius. From one perspective,
these results may be interpreted as a positive development for S. s. sasin
as the growing population represent an overall increase in the S. sasin
population, and the expanding population contains a significant
representation of S. s. sasin alleles.