What do ground squirrels have in common with ancient sailors, bees, birds, and sea turtles? According to a new study, they have just been added to the list of creatures known to navigate by the Sun.
Like all squirrels, Cape ground squirrels (Xerus inauris) temporarily store their food stash in several hiding places at once to guarantee a snack at a later date. At the Kalahari Research Centre in South Africa, where these squirrels were studied in the wild, there aren’t many obvious landmarks such as trees and bushes in the arid landscape to use as reference points, though. The researchers, from the University of Zurich (UZH), found instead that the squirrels orient themselves using the Sun – which is almost always visible over the Kalahari – to hide and then return to their cache.
"The squirrels probably use the position of the Sun as the most important cue to roughly adjust their direction of movement," explained co-author Jamie Samson, from the Department of Evolutionary Biology and Environmental Studies at UZH, in a statement.
To test this, Samson and co-author Marta Manser left out food for the squirrels to take. When they grabbed the food and ran, they tracked them with a GPS and discovered that the squirrels all moved in an almost straight line directly towards or away from the Sun at consistent azimuth angles, which the authors describe in their paper published in Scientific Reports as “the angle of the Sun in relation to a fixed reference, such as true north.”
Cape ground squirrels are sociable little creatures. Brittany Sumner/Kalahari Research Centre
"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," Samson said in the statement.
The researchers then set up cameras near their hidden stores and waited to see if the squirrels also used the Sun as a navigation tool to reclaim their cache; they tested this by recording the time of day they originally hid their food and then when exactly they returned to get it. It turns out the ground squirrels returned to their hoards almost exactly 24 hours later – when the Sun was in the same position in the sky as it had been when they first buried them.
However, what makes this study really interesting is that the squirrels were flexible with their schedule, sometimes collecting before the 24 hours were up if they thought their stash was under threat from thieves – though always when the Sun mirrored the 24-hour azimuth angle.
Although the authors claim that “to our knowledge this is the first study on wild mammals to describe such strategic use of the sun in this way,“ they do note that “a number of studies have suggested this cue has to be used in combination with other information, such as landmarks.”
As the squirrels appeared able to recover food when the Sun was in a different position to when they buried it, meaning they could be using other cues in conjunction, the authors conclude: “We suggest that this flexibility may have evolved due to the high risk of caches being stolen, and animals have developed a problem specific strategy.”
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