Appreciating Ecosystem-enhancing Engineers: Ground Squirrels

Darting and dodging, they swiftly avoid hazards, like cars and predators, with surefire grace and boundless courage. With its roster of alarm calls and defensive moves, the nose twitching, tail flicking, bright-eyed California ground squirrel is a surprisingly important species—and more than worthy of a place at the table for Squirrel Appreciation Day on January 21!

“Ground squirrels are ecosystem engineers,” said J.P. Montagne, research coordinator at the San Diego Zoo Institute for Conservation Research. This keystone species also plays a key role in our burrowing owl restoration project. “Burrows dug by the squirrels are a necessary resource for burrowing owl populations, so we have translocated groups of around 50 squirrels to protected areas suitable for the owls.”

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Camera traps capture “wild” moments in the field, like this burrowing owl eyeing up a ground squirrel.

Ground squirrels are important to species like the burrowing owl that depend on a particular grassland ecosystem. The pint-sized rodents actually help to restore degraded grasslands that have been invaded by thick, nonnative, thatch grasses, which native species cannot survive in. The digging habits and voracious appetite of the ground squirrel do much to open up the landscape to many native species, including the burrowing owl. “This project is unique because we are using one species, the ground squirrel, to help save another, the burrowing owl,” said J.P.

However, it is no easy task to relocate these nimble rodents to “new digs.” One drawback was that the squirrels don’t like much clay in their soil. The biggest challenge to the translocation process is that many predators like red-tailed hawks and rattlesnakes keep squirrel at the top of their menu. “It can be heartbreaking to work with a prey species,” said J.P. He insists that squirrels are fascinating behaviorally. “They have different alarm calls for different predators and can recognize various aerial predators from their silhouettes in the sky.”

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Coyotes are one of the many predators of ground squirrels.

Researchers keep tabs on the translocated squirrels by marking each with a letter and number code—using temporary dye that lasts one to five months—so individual animals can be identified. They also use camera traps and live traps. Each animal was ear-tagged as well as PIT-tagged, which can be read with a scanner (like a chip in a pet). “Through trapping and observation, we can follow individual animals and monitor the success of the project and modify accordingly.” J. P. was pleased that one adult male squirrel in particular, that was moved into a control area, proceeded to create a huge underground burrow system. Later, “he would perch on a stump to survey the area and watch out for predators.” He also sired a litter (or “scurry”) of squirrels. Success!

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Ground squirrel juveniles soon to be released.

One unforeseen advantage of the drought in our region meant that fewer raptor chicks survived, which gave the ground squirrel population a boost. “In 2015, about 52 squirrel babies survived, and we would have been happy with 20,” said J.P. excitedly. That means the industrious little rodents can keep digging burrows, something the owls are sure to appreciate every day!

Karyl Carmignani is a staff writer at San Diego Zoo Global. Read her previous story, Wonderful Wu.

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  1. Paul