A somewhat late report on the “newest” species of North American bird, the Cassia Crossbill. As occurs annually, the taxonomy of birds in the U.S. and Canada is reassessed by the American Ornithological Society. In 2017 this group was split off into its own species for the first time. This bird has been studied in SE Idaho for years. According to Audubon.org,
“While most crossbills wander widely, this type is very sedentary, staying in the South Hills and Albion Mountains of southern Idaho. The cones of lodgepole pines in those ranges offer a steady supply of seeds for the crossbills to eat, apparently because there are no squirrels there to compete for them—and so the new species name sinesciurus means “without squirrels.” The new crossbill’s English name honors Cassia County, Idaho, which includes the complete known range of the species. North America already has birds named for cities (like Philadelphia Vireo), states (Kentucky Warbler), and countries (Canada Goose), but this may be the first one named for a county.”
Bird taxonomy, like that of many other taxa (category levels), is fluid. Many factors are considered when reclassifying or changing the names of individual species to reflect its relationship to other like species. DNA markers and purported evolutionary relationships feature prominently in this effort today. This is a Catch 22 as the relationships used to classify a creature are continually in flux and relative to one another.
It is encouraging that extent of interbreeding with other red crossbills, vocalizations, and depth of beak among other characteristics were primary in classifying the Cassia crossbill as distinct. The type of work done by Dr. Benkham prioritizes natural history and morphological differences which provide empirical evidence for splitting off this group. Though Benkahm attributes this distinction to co-evolution between crossbills and lodgepole pines, the empirical evidence points to natural selection working at the species level catalyzed by an herbivore-producer relationship. Yet another example of connecting a specific instance of observable natural selection at work to the grand evolutionary narrative.
Photo by Craig Benkman, the primary researcher on this project, from the University of Wyoming.