The Sun Leads Ground Squirrels Back to their Buried Nuts

September 12, 2016 | Erica Tennenhouse

Photo credit: Brittany Sumner, Kalahari Research Centre

In the Kalahari Desert, where physical landmarks are scarce, ground squirrels have come to rely on the sun’s azimuth angles to locate cached food.

When a ground squirrel in South Africa’s Kalahari Desert comes into possession of a prized nut, it quickly gets buried underground for safekeeping. But with few obvious features like bushes or trees adorning the barren desert floor, the ground squirrels must find other means of keeping track of where their many caches of food are located.

According to new research published in Scientific Reports, the sun, which is almost always visible in the daytime over the Kalahari, serves as an important reference point for the recovery of cached food by ground squirrels.

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Researchers gave several ground squirrels peanuts, and watched to see which direction they scurried to hide their spoils. Remarkably, the squirrels tended to move in nearly linear lines at consistent azimuth angles, which the authors describe as “the angle of the sun in relation to a fixed reference, such as true north.”

"Based on this movement pattern, we presume that Cape ground squirrels use the position of the sun at a particular time of day as a rule of thumb to find their bearings when searching for a place to hide their food,” study lead author Jamie Samson of the University of Zurich said in a press release.

It’s probably no coincidence that the ground squirrels tended to retrieve their hidden food almost exactly 24 hours after burying it, when the sun was in the identical position of the sky. The schedule was variable though — if there were many other group members around, the ground squirrels would recover their food earlier to ensure thieves didn’t get to it first. But in these cases, they would, nonetheless, pick a time of day when the sun mirrored the 24-hour azimuth angle.

The authors conclude that theirs is the “first study on wild mammals to describe such strategic use of the sun in this way,” and they propose that the ground squirrels have evolved this flexible food retrieval strategy in response to the high risk of their reserves being stolen.

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