When owls find a mouse, they swallow it whole, and then cough up the bones in a brown walnut-sized pellet called a bolus. While animal puke wouldn’t generally be the type of thing parents would want to hunt for, dissecting a bolus is a fascinating activity. With steady hands, a bit of anatomical knowledge, and a lot of patience, one can often prise an entire mouse skeleton from the bolus, and stretch it out to take a look at it. Besides being creepily fascinating, this is a great science activity with illustrative lessons about predators, prey, and the digestive process.
You can order boluses (boli?) on the Internet, but they’re also out there in the woods just waiting to be picked up, anywhere where owls roost at night. One particularly lucky San Francisco spot is just inside the Presidio, at the Presidio Gate at Presidio Boulevard and Pacific Street. Owls like to hang out in the nearby pine trees at night, gulping down mice (and the occasional gopher) and spitting them out like so many sunflower seed shells. A nature walk in the early morning can yield spit-up fruit. Look for dark brown balls on the ground underneath the trees. Happy dissecting!


