As we got closer to the spot where we thought the mammal had been, we started watching more carefully among the shrubs and flowers. It took a few minutes, but then we got lucky and spotted it. It's in the picture below. Can you see it?
Here's a closer view as the animal rose up (like a periscope) and looked to the side:
And another showing a head-on view, the short front legs, and the long tail with the black tip (held out to the right).
This is a Long-tailed Weasel (Mustela frenata). I must admit, although I'm not prone to naming "favorites," I love every opportunity to observe this species. And this individual was actively hunting right in front of us.
It kept diving into the shrubs and then popping up somewhere new. And finally it emerged with prey!
Long-tailed Weasels are carnivores, primarily pursuing small- and medium-sized mammals such as voles, mice, and pocket gophers. But they're known to be generalists and may switch to alternative prey when it's available. Although Long-tailed Weasels are relatively small (~11-20 inches long, including the tail), they can subdue sizable prey.
I'm actually not 100% certain what this weasel caught. In the field, we wondered if it was a young pocket gopher, but after reviewing the pictures I'm not sure. I need some help from folks who have more experience with West Coast mammals! Here are several views of the prey (below). If you have thoughts about its identity, it'd be great to hear them.
May and June seem to be the best months to see Long-tailed Weasels on Bodega Head. Adults are probably feeding young at this time of year, so they are out during the daytime a bit more than usual.
Long-tailed Weasels aren't common, so it's a lucky day when you see one. But keep an eye out for a narrow brown back bounding among the grasses, or a black-tipped tail disappearing between the shrubs.
ADDENDUM (13 May 2013): Okay, I've heard back from a few people, and the verdict is that the prey item is a vole. Although it looked big in the field, the legs are narrow, the feet are small, and the ears are large — all characteristics pointing to vole rather than gopher. Thanks to everyone who provided feedback and assistance!