Creature Feature: Humboldt's flying squirrel

August, 2017

Humboldt Flying Squirrel - Glaucomys oregonensis



Humboldt flying squirrel on a tree trunk

It turned out that the squirrel was hiding in plain sight. Humboldt’s flying squirrel is a cryptic species, closely resembling in appearance another flying squirrel, the northern flying squirrel. There are slight differences—Humboldt’s flying squirrel is slightly darker and smaller—but because the two species had overlapping ranges, scientists had assumed that these differences were unimportant. 

Scientists recently announced a “new” mammal species that calls our redwood forests home: Humboldt’s flying squirrel (Glaucomys oregonensis). The squirrel, named after the famed naturalist Alexander von Humboldt, is now the third species of North American flying squirrel and the 45th in the world. 

But those small differences puzzled researchers. Curious to see if there was something more at play, biologists collected DNA samples from 185 squirrels—some from recently killed squirrels and others from old museum samples. The results surprised scientists. Looking at the nuclear genome, they saw a clear and distinct split—two branches on the family tree diverging.

It is thought that the species diverged as a result of the last ice age. A northern population of squirrels became cut off from a southern population by glaciation. Isolated from each other, the two different populations diverged on separate ecological paths. Eventually, they became so different from each other that when the glaciers melted and the two populations came in contact again, they didn’t interbreed. (The fact that they don’t interbreed or “hybridize” shocked researchers, as the other two species of North American flying squirrels hybridize). Scientists are puzzled as to what is keeping these two species from breeding. Is it behavioral or are they so physically different that they can’t interbreed?

Humboldt’s flying squirrel ranges the West Coast, from British Columbia in the north to the bottom of the Sierra Nevada forests. In its northern range, Humboldt’s flying squirrel shares its forests with its cousin, the northern flying squirrel. Although the two squirrels look alike and share the same forests, they do not interbreed.

Humboldt’s flying squirrel generally prefers older forest types, where it can launch itself from high branches to soar to another tree. Using a membrane that runs from its front legs to its back as a sail and its poofy tail as a rudder, the flying squirrel can glide up to 100 meters in the air. The squirrels forage at night, looking for berries, nuts, fungi, carrion, and bird eggs. They, in turn, are hunted by predators like the northern spotted owl, Pacific fisher, and the Humboldt marten. 

The flying squirrel’s “discovery” is a good example of the impact that cheap, high-resolution genetic studies have had on the field of taxonomy. In some cases, genetic research has determined that there are less differences than we had previously thought—such as recent research that shows that coastal martens in Oregon and California are actually one subspecies and not two. In other cases, like this one, scientists can discern separate species from physically similar individuals with overlapping ranges. Expect more discoveries like Humboldt’s flying squirrel in the future as genetic tests become cheaper, faster, and easier to perform.

New genetic studies also have regulatory implications. To the degree that a single species can be “split” into multiple species, the more likely it is that one of these new species is eligible for protection under the Endangered Species Act. Similarly, if two species can be “lumped” into one species, the protections afforded could diminish. 



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