Data from: Extreme elevational migration spurred cryptic speciation in giant hummingbirds

The eco-evolutionary drivers of species niche expansion or contraction are
critical for biodiversity but challenging to infer. Niche expansion may be
promoted by local adaptation or constrained by physiological performance
trade-offs. For birds, evolutionary shifts in migratory behavior permit
broadening of the climatic niche by expansion into varied, seasonal
environments. Broader niches can be short-lived if diversifying selection
and geography promote speciation and niche subdivision across climatic
gradients. To illuminate niche breadth dynamics, we can ask how ‘outlier’
species defy constraints. Of the 363 hummingbird species, the giant
hummingbird (Patagona gigas) has the broadest climatic niche by a large
margin. To test the roles of migratory behavior, performance trade-offs,
and genetic structure in maintaining its exceptional niche breadth, we
studied its movements, respiratory traits, and population genomics.
Satellite and light-level geolocator tracks revealed an >8,300-km
loop migration over the Central Andean Plateau. This migration included a
three-week, ~4,100 m ascent punctuated by upward bursts and pauses,
resembling the acclimatization routines of human mountain climbers, and
accompanied by surging blood-hemoglobin concentrations. Extreme migration
was accompanied by deep genomic divergence from high-elevation resident
populations, with decisive postzygotic barriers to gene flow. The two
forms occur side-by-side but differ almost imperceptibly in size, plumage,
and respiratory traits. The high-elevation resident taxon is the world’s
largest hummingbird, a new species that we describe and name here. The
giant hummingbirds demonstrate evolutionary limits on niche breadth: When
the ancestral niche expanded due to evolution (or loss) of an extreme
migratory behavior, speciation followed.