26 June 2025

This morning when I opened Cornell Lab’s Birds of the World website, the featured photo was a lesser horned owl (click the link to see it). I’d never heard of a “lesser” for two reasons. (1) It’s a relatively news species split from the great horned owl about a decade ago and (2) it lives in part South America where I’ve never been — Peru to Tierra del Fuego.

Great horned owls range from the Arctic into South America with so much regional variation that today, even after the split, there are 14 subspecies. The nominate subspecies, Bubo virginianus virginianus is the owl we’re familiar with in Pittsburgh. The lesser horned owl used to be a subspecies Bubo virginianus magellanicus of the great horned owl so he’s sometimes called the Magellanic owl.

What’s the difference between the two? Weight! The heaviest lesser horned owls (1,335g) weigh about half that of the heaviest great horned owls (2,500g).

Bolstering the evidence that they deserve to be split, a team of scientists led by Emily N. Ostrow conducted a DNA study of great horned owl subspecies including magellanicus and found that the subspecies’ DNA diverge in Peru.

Range-wide phylogenomics of the Great Horned Owl (Bubo virginianus) reveals deep north-south divergence in northern Peru
— by Emily N. Ostrow?, Lucas H. DeCicco, Robert G. Moyle published in PeerJ

And that’s where the lesser horned owl’s range begins — in purple below.

Fortunately the two owls’ ranges do not overlap so you won’t need to do a DNA study to know you’re looking at a “lesser” in southern South America.