Banding data show hummingbirds have high rates of hybridization

Abstract

Abstract We estimate hybridization rates among hummingbirds using nearly a million banding records from the United States and Canada. Annually from 2006 to 2019, an average of 44,600 individual hummingbirds and 14 hybrids were banded. Nearly all reports of hybrids come from localities west of the Mississippi, where multiple species breed in sympatry, whereas only Ruby-throated Hummingbird (Archilochus colubris) breeds east of the Mississippi. Adult male hybrids comprise 62% of all hybrids banded, a significantly greater fraction than “regular” adult males, which are 29% of all birds banded (excluding Ruby-throated Hummingbird). We infer that this excess of adult male hybrids is caused by ascertainment bias: banders more often misidentify female hybrids as parental species because females mostly lack species-specific showy sexual ornaments of male hummingbirds, making them harder to identify, rather than Haldane’s rule of reduced survivorship of the heterogametic sex. Also influencing the apparent hybridization rate are banders, a few of whom seek out or avoid hybrids. After considering these biases, the data suggest that, in areas of the United States and Canada with >1 species, approximately 1 hummingbird in a thousand (0.1%) is an F1 hybrid.