Redpoll Revelation: Uniting Two Birds into One Species

Assistant Professor Nicholas Mason and his collaborators published a groundbreaking paper in 2021 that will soon introduce significant changes to the classification of bird species. Their research, spanning a decade, focuses on the Redpoll, a bird that Mason has studied throughout his career. During his graduate studies, Mason, along with a team of researchers from CU Boulder, Iceland, and the Czech Republic, made a pivotal discovery about the Redpolls of North America: what were previously believed to be two distinct species of Redpolls are now understood to be a single species.

"By sequencing the genomes of these birds, we can identify connections between specific genomic regions and their physical traits," explained Mason. "There's this one really big chromosomal inversion on one of the larger chromosomes, and if you have one genotype where if it's flipped one way you tend to like a certain type of bird. When you have the other form of the inversion, it looks like the other type. Those types can interbreed."

Redpolls, which inhabit Canada, Europe, Russia, and the northern United States, exhibit varied appearances and migratory behaviors. Their diet primarily consists of seeds, which can vary widely in their availability from year to year. Mason noted that northern Redpoll populations—formerly known as the Hoary Redpoll—generally have a lighter coloration and shorter bills, while those in the south—formerly known as the Common Redpoll—tend to be darker with longer bills. This diversity in appearance is largely attributed to the chromosomal inversion in their genomes.

"What it seems like is that there is this phenotypic continuum in variation among populations that we used to think were different species, but is really just attributable to a big part of this chromosomal inversion in their genomes," Mason said. "It's been a long winding path for ornithologists to conclude that these are better treated as a single species."

In the field of ornithology, changes to bird species classifications are subject to approval by a panel experts, and a revised classification is published each year. Mason, a member of the American Ornithological Society's North American Classification Committee (NACC), shared that after a decade of rigorous discussion, the committee has agreed with the latest findings and will be reclassifying the Redpoll as a single species. In addition to Mason, the NACC includes many graduates of the ornithology program at the LSU Museum of Natural Sciences (LSUMNS), which has had an outsized role in revising and improving taxonomic classification of birds over many decades. This taxonomic ‘lumping’ of multiple species into a single species of redpoll is the latest example to how LSU ornithologists are applying new technologies to better understand the evolutionary history and taxonomy of birds.