Pocket Mice Powerhouses

Pocket mice may look small and delicate, but they are little powerhouses when it comes to digging burrows!

Pocket mice may look small and delicate, but they are little powerhouses when it comes to digging burrows!

Pacific pocket mice, like many small rodents, build burrows as their homes. Instead of living above ground, they dig out tunnels and chambers where they are safe from most predators, can store surplus food, keep cool during hot, summer days—and warm during the winter!

Just by looking at a pocket mouse, you wouldn’t necessarily guess they are great diggers. They have tiny paws to go with their tiny bodies and don’t seem like they could move that much dirt, especially when it is dry and hard packed.

A burrow add-on in a trap! There is a tiny opening a few inches to the left of the trap. There is a slightly larger burrow entrance, probably to the same burrow system, another 18 inches or so to the left of the trap.

A burrow add-on in a trap! There is a tiny opening a few inches to the left of the trap. There is a slightly larger burrow entrance, probably to the same burrow system, another 18 inches or so to the left of the trap.

This summer in the field, I got a first-hand look at just how well suited these guys really are to their subterranean lifestyle. We set out a trap next to what looked like a good pocket mouse burrow (these are Los Angeles pocket mice, closely related to the Pacific pocket mice we are breeding at the San Diego Zoo Safari Park). Their burrow entrance is roughly the size of a penny, so you have to be looking closely to find them! When we came back a few hours after dark (which is prime activity time for pocket mice), we found out we were correct: there was indeed a pocket mouse living there.

Field assistant Aliya McCarthy holds the super trap. It was full of dirt!

Field assistant Aliya McCarthy holds the super trap. It was full of dirt!

But instead of just walking into the trap to get the food in the back, it had started filling it with dirt like it was an addition to its burrow system! Even more surprising, as we approached and were marveling at it, the pocket mouse ran from its burrow and into its newly modified trap-burrow! Obviously it already felt right at home. Like a “real” burrow, this one had a narrow entry space and an open chamber in the back.

I videotaped another Los Angeles pocket mouse that was busy tidying up her tunnel and pushing the extra dirt out of the opening:

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It’s fascinating studying these little guys in the wild, and seeing how they are also displaying their natural behaviors in our managed-care facility! (see The Art of Burrow Making)

Rachel Chock is a graduate student and volunteer with San Diego Zoo Institute for Conservation Research’s Pacific pocket mouse project. Read her previous post, Badger and Coyote Caught on Camera.

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