GENERATIONS: Evan Hazard: “Golden” gophers this time
Time to get back to my promised column on Thirteen-Lined Ground Squirrels (“tridecs”). You may remember that last November I wrote that pocket gophers belong to a strictly New World family, the Geomyidae. Tridecs belong to the Sciuridae (squirrel family), inhabiting all the continents except Australia and Antarctica.
This large family comprises five subfamilies, one of which, the Xerinae, includes the tribe Marmotini: some 67 species of chipmunks, prairie dogs, ground squirrels, and the marmots themselves (woodchucks and various New and Old world mountain-dwelling marmots).
Until recently, most ground squirrels were lumped in the genus Spermophilus, but that genus is now restricted to the Old World susliks, some 16 species.
The greatest diversity of ground squirrels occurs in North and middle America. We have three in Minnesota: Franklin's Ground Squirrel (Poliocitellus franklinii), Richardson's Ground Squirrel (Urocitellus richardsonii) and Thirteen-Lined Ground Squirrel (Ictidomys tridecemlineatus). Tridecs are the most widespread of three species of Ictidomys. The other two species inhabit the American Southwest and northern Mexico.
Digression: The small antelope ground squirrels, Ammospermophilus, were split off from Spermophilus decades ago. Other subgenera now considered genera in their own right include Poliocitellus, Urocitellus, Ictidomys, Notocitellus and Otospermophilus.
That last one, same genus as the common Beechey Ground Squirrel of the Pacific states, rang a bell, so I searched for “evan hazard citellus rexroadensis.” That went to the free abstract of a short 1961 article, “The Subgeneric Status and Distribution in Time of Citellus rexroadensis.” And yes, the Pliocene fossil teeth and jaws I was studying are now Otospermophilus rexroadensis. My article had pointed out that, based on dental characters, C. rexroadensis had been classified by others in the subgenus Otospermophilus. It resided in mid-continent North America for perhaps 2-3 million years in the Pliocene Epoch, 5.3-2.6 million years ago.
Back to tridecs: Some members of the Marmotini, including both New and Old World mountain-dwelling marmots, are colonial, but tridecs are not. On the E.S. George Reserve in southeastern Michigan, where I studied behavioral interactions among sciuridae in the '50s, their burrows were concentrated in some open areas more than others, but that apparently reflected a preference for low, moist swales rather than chumminess.
Incidentally, nobody called me on what looked like poor usage in my November column. I had written, “Eastern Gray Squirrels (Sciurus carolinensis) and Eastern Chipmunks (Tamias striatus) are common on the berm and in adjacent woodlands, and the Eastern Cottontails (Sylvilagus floridanus) in my backyard probably also inhabit Salisbury Plain. Also, two mammals common on Salisbury Plain were Plains Pocket Gophers (Geomys bursarius) and Thirteen-Lined Ground Squirrels (Ictidomys tridecemlineatus).”
Well, why might that be poor usage? In The Elements of Style, my favorite writing manual, Strunk and White suggest that, in an account, writers should choose a tense and stick to it. I changed tenses: some critters “are common” and “also inhabit” but “two mammals common on Salisbury Plain were” gophers and tridecs.
Was I asleep at the switch? No, that was deliberate, for two reasons. First, I wondered if anyone would question my usage. None did, but then, most of my readers are Minnesotans. Two, it reflected the actual situation on Salisbury Plain in 2018. I don't claim to have examined every square meter from the berm north to 34th Street. But I walked across that field dozens of times, using different routes, and never found a gopher mound all summer. Sanford Health hayed Salisbury Plain last summer, leaving long rows of cut hay before baling. Looked up and down the cut swaths between the rows: no gopher sign.
Tridecs don't make mounds, just simple holes in the ground, so their work is harder to spot. But most summers I see occasional tridecs on the lawns. None at all in 2018. Also, no sign of badgers digging out gophers or tridecs. No obvious differences in food or water availability, or increases in sightings of potential predators. So what happened to my gophers and “gophers”? Beats me. Hope they show up in summer 2019.
Evan Hazard is a retired BSU biology professor.