predation

August 8, 2025: Learning to Hunt

Posted on by Tim

Early August can be a boring time of year for birders. Not only are birds keeping a low profile due to the heat and lack of need to defend a territory, many of them are in heavy molt and looking their scraggliest. Birders often choose to pursue other hobbies during this time of year, and dream of fall migration, which begins in earnest next month. However, if rather than looking for lots of species, you instead focus on watching bird behavior, August can actually be quite fun. It’s the time of year when fledgling birds are at their goofiest!

This week, we’ve returned to Blue Oak Ranch Reserve, and while holding office hours on the back porch of the barn, I’ve had plenty of time to watch some youngsters. While watching California Thrashers learn to flip leaves over and observing Western Bluebirds trying to fly catch has been fun, I’ve particularly enjoyed the antics of the young birds of prey. For some reason, this was an exceptional year for rodent abundance. Particularly voles and deer mice have been just everywhere. The bad news—that seems to have meant an abundance of ticks. The good news—there was plenty of food for baby hawks and owls.

Many birds of prey lay extra eggs beyond what the parents could feed in a normal year. In most years, the last one or two birds to hatch end up getting bullied by their siblings and tend not to make it out of the nest. This year however, the abundance of food led to a higher than average fledge rate. Now, many of the youngsters, still recognizable by their unique plumages, are trying to hunt on their own. And I hate to say, but it does not seem to be going well.

While there are juvenile Red-Tailed Hawks everywhere, one bird in particular has taken up residence in the big valley oak tree by the back of the barn. Every twenty minutes or so for large parts of the day, the youngster swoops down over the large ground squirrel colony, eliciting a chorus of chirps. I don’t know if it’s the approach, the angle, or the speed, but I’ve watched maybe twenty failed attempts. The poor juvenile ends up standing sullenly on the ground before retreating back to the oak tree to sulk before trying again.

We also have a resident juvenile Cooper’s Hawk that’s not faring any better. Cooper’s Hawks specialize on hunting medium sized birds in forested areas. However, this individual doesn’t seem to have gotten the memo. I’ve watched them dive for a ground foraging finches a couple of times, and even make an attempt at a vole without any success. Maybe an apprenticeship program would help them learn some better techniques.

The night shift at BORR is currently being dominated by American Barn Owls in numbers like I’ve never seen. I haven’t seen any hunting occurring—it’s a little harder to watch in the dark. But based on the number of frustrated shrieks and hisses I’ve been hearing, I don’t think it’s going any better.

The coolest failed predation attempt I watched, was from a young Golden Eagle. This largest of raptors dove after a ground squirrel thirty feet away from, missing pretty badly. Unfortunately, junior was subsequently driven away from the area by a team of Common Ravens and Red-Tailed Hawks.

Luckily with the ongoing rodent boom, everyone will have essentially unlimited attempts to perfect the craft of hunting. I hope the practice goes well, and I’ll actually see some successes by the time I return next month.

May 18, 2025: Gordon and Blondie

Posted on by Tim

I’m wrapping up the spring run of the California Ecology and Conservation class this week. That means a lot of sitting on the back deck of Blue Oak Ranch Reserve (BORR) barn while I answer questions from students and complete administrative tasks. My ever-present companions are the dozens of California ground squirrels (Otospermophilus beecheyi) that live in an enormous colony next to the barn. By now, I have accidentally accrued hundreds of hours of behavioral observations of these prairie-dog-like mammals. They are endlessly entertaining to watch as they scurry about the important business of eating seeds and chasing neighbors.

              Despite, or maybe because of their abundance, squirrels are under constant threat of being eaten by many species of birds, mammals, and snakes. Several times a day, a squirrel in the colony sounds an alarm. Ground squirrels actually have two types of alarms. The first is a single loud whistle, often given in response to an aerial predator like a hawk, which means “duck and cover”. At the call, squirrels will drop what they’re doing and run into the closest hole. The second type of alarm call is a descending chattering that often morphs into a high, regularly spaced beep. That one must mean “look around”, because when it’s sounded, everyone stands up on their back legs as surveils the field for a bobcat or fox. This time of year, you can only see their little heads poking up above the tall grass. Humans can cause the squirrels to make either type of alarm, especially in colonies far from the barn. When I hike up to the distant areas of the reserve that experience far fewer human intrusions, my presence is heralded with chatters and beeps from a half mile away. On the other hand, strolling directly through the colony by the barn will barely illicit a chirp from the jaded resident squirrels.

Amazingly rattlesnakes generate a different, third predator response in ground squirrels—the tail flag. I’ve watched a squirrel alert to a rattlesnake and then approach it quite aggressively, wagging its tail rapidly back and forth. The snake, apparently relying on a stealthy approach, gave up the hunt and retreated down a hole, despite the squirrel clearly being within striking range. I don’t fully understand why the tail flag works, but it’s a scientifically supported method. Researchers have simulated rattlesnake strikes and found tail-flagging squirrels are better able to leap away. They’ve also found that snakes are more likely to leave the area in response to an approaching flagging squirrel than a non-flagging one.

Despite all the alarming, squirrels get got. A lot. On the reserve. I’ve seen predation by bobcats, coyotes, Red-Tailed Hawks and a Golden Eagle. With all the predators around taking their toll, there’s lots of turnover in the individuals in the squirrel colony. Two notable squirrels that didn’t seem to make it through this past winter were Gordon and Blondie. Gordon was a squirrel particularly acclimated to humans. He developed a preference for dining on the food waste bucket, even scampering into the kitchen to steal treats. His healthy appetite had some serious health consequences—he was the fattest ground squirrel I’ve ever seen. When I showed back up this spring, all the squirrels were slim, trim, and relatively meek. Based on past behavior, by the end of fall, this year’s generation will learn the art of stealing human food and splooting their chonky bodies on the back deck before too long.

Blondie was another squirrel that lived next to the barn who had exceptionally light fur. Ever since I’ve been visiting BORR, a small number of squirrels in the barn colony have been blonde. Their color does blend in quite well once the grass dries out, but they stick out like sore thumbs in the spring when the grass is green and the pups are young and vulnerable. Presumably the genetic mutation in fur color was able to persist in the barn colony because all the human activity results in fewer predators locally. At least until this year. Despite searching for them this spring, I couldn’t find blondie or any other lighter-furred squirrels this spring. This year’s generation of pups are just emerging from their dens now. It will be interesting to see this summer if any of them are Blondie Juniors. I’ll definitely be looking out for them as I resume my squirrel watch five weeks from now.