Digging into Burrowing Owl Recovery
I’m in south San Diego County, walking down memory lane, visiting our burrowing owl project site. I take in the view: gentle hills covered with golden grasses and dotted with the occasional sumac, scrub oak, or clump of buckwheat. It’s not pristine, it’s not even all native species, but this is big-sky country and I like it.
Maybe it’s because I imprinted on scenes like this when I was studying California ground squirrels for my Ph.D. dissertation, more than a few years ago. The scene is not atypical—little of our native grasslands in California remain intact. Long ago cattlemen brought in Mediterranean grasses, and the land has never been the same since. Along with the change in plant communities, many of our native animal populations have also failed to adapt to the thick thatch typical of these annual grasses: kangaroo rats, pocket mice, and burrowing owls, to name a few of the now conservation-dependent species we work with here at the San Diego Zoo Institute for Conservation Research.
Turning back the clock to pristine native grass and forb lands will not be possible. But we can do something.
I look with satisfaction at the healthy number of burrows in the ground. A year ago there were none here; our hard work is paying off. In an effort to restore these protected lands, we’ve been bringing in California ground squirrels, a “keystone” species that helps engineer the grassland ecosystem. The idea is that squirrels will dig burrows and help open up the vegetation, a state burrowing owls prefer.
It won’t be native plant habitat, but its structure will be more like what once was here. Squirrels’ voracious appetite and digging will reduce some of the excess plant matter that is keeping other animals away. And, keeping the nonnative grasses down may give some of the native plants and animals a chance to make a small comeback.
It hasn’t been an easy path, and we’ve learned some lessons along the way. Translocating squirrels isn’t easy. This may come as a surprise because you wouldn’t think a “pest” species would be that sensitive. But we’re finding it more difficult to relocate ground squirrels than the endangered Stephens’ kangaroo rat! Many don’t like to stay put where we release them and move long distances from the release site, spreading out across the landscape. Squirrels are also the “popcorn” of the grassland community: everybody likes to eat them, and it’s hard to eat just one! Sadly, we find their remains under hawk nests and in coyote scat all too frequently.
We go to great lengths to get our squirrels established. First, we capture them at sites where landowners don’t want them around. We catch and release groups that are familiar with each other. We move them to above ground-below ground acclimation chambers, where they spend a week at the site before we let them out.
Working with San Diego State University, we weed-whack back all the thick non-native grass. We bring in cover—logs and branches—that squirrels can use to hide under, burrow under, or stand atop to look for predators. We provide sweet, juicy slices of apples and yams for a few months after release. And, we monitor them closely after release, using camera traps, live traps, radiotelemetry (for some) and direct observations. We’re getting squirrels established and burrows dug, so it is a success, but we would like to increase our success.
Looking forward, we hope to get better at selecting sites and translocating squirrels. We’ve been working on a “habitat model” to determine the precise habitat characteristics where squirrels will thrive. So far, it looks like the best predictors of ground squirrel presence are soil type (not too soft, not too hard!) and cover to hide from predators.
And, of course, we have plans to work more directly with the burrowing owls themselves. We’ve been monitoring a few burrowing owl nests (in squirrel burrows!) and are beginning to learn more about what they need for nesting and foraging habitat.
Next year, we’ll do more of this, and we may also work with some of our local partners to build some artificial burrows for the owls. This strategy is a good short-term fix, but we will also work hard on the long-term solution: habitat restoration and bringing back California ground squirrels.
Ron Swaisgood, Ph.D.
Director, Applied Animal Ecology, San Diego Zoo Institute for Conservation Research