More about Marmots

Two weeks ago today, I saw the first Yellow-bellied Marmot of the year, which I shared in a blog post a few days later. I mentioned their habit of estivating (going undergrown and entering torpor during the heat of summer) and then continuing straight into hibernation for the winter.

Anyone near agricultural areas will realize, however, that not all marmots estivate, that some remain active into the Fall and don't go underground to stay until it's time to hibernate. This difference in behavior is a response to irrigation. It's not so much the heat that causes normal populations to estivate--it's the lack of moisture. And so where farmers have the ability to keep the water flowing throughout the summer months, their crops will be an attraction to "rockchucks," especially younger ones (which typically stay out longer than adults anyway). In Central Oregon, these opportunists can be especially hard on alfalfa, as are the colonies of smaller rodents, Merriam's Ground Squirrels (Spermophilus canus) and Belding's Ground Squirrels (S. beldingi).

But whereas these large rodents can be a significant nuisance to farmers, they likewise play a significant role in the ecology of the region. I have firsthand knowledge of this from years spent climbing into the cliff nests of local Golden Eagles (Aquila chrysaetos).

Throughout much of the intermountain West, Golden Eagles are first and foremost predators of jackrabbits. But here in Central Oregon, we don't have the healthy populations of Black-tailed Jackrabbits (Lepus californicus) that used to be here. As a result, biologists from the Oregon Department of Fish and Wildlife wanted to know just what our Golden Eagles were eating. I was hired by them a few years back to climb or rappel into the nests of eagles to collect prey remains and regurgitated indigestibles to ascertain just that.

The result of those nest searches was a long list of species of mammals, birds, reptiles, and fish eaten by nestling Golden Eagles. The eagles in this area bring a wide variety of prey to feed their young, including most any animal large enough to be captured. (The size of an eagle's foot and talons precludes their capturing small perching birds and smaller mammals like chipmunks and mice.) But though the diversity of prey taken was the most important finding of that research, a secondary conclusion is pertinent to our present blog topic. In lieu of jackrabbits, Yellow-bellied Marmots appear to be the single most important prey--in terms of biomass--of Golden Eagles in our area during the breeding season.