Ground squirrels, belonging to a group of 62 species of terrestrial rodents, exhibit a remarkable adaptability in their dietary habits. These diurnal creatures, characterized by their burrowing lifestyle, short legs, strong claws, and small ears, occupy diverse habitats across North America, Eurasia, Africa, and even Southeast Asia. Their diet, largely omnivorous, reflects this adaptability, varying significantly based on species, habitat, and seasonal availability.
Dietary Diversity Among Ground Squirrels
Most nontropical ground squirrels are omnivorous. The thirteen-lined ground squirrels exemplify this dietary flexibility. At least 50% of their diet consists of animal matter, including grasshoppers, wireworms, caterpillars, beetles, cutworms, ants, insect eggs, mice, earthworms, small birds, and even other thirteen-lined ground squirrels. The vegetative portion of their diet is composed of seeds, green shoots, flower heads, roots, vegetables, fruits, and cereal grains.
Other ground squirrel species exhibit similar omnivorous tendencies. Franklin’s ground squirrel consumes a wide variety of green plant parts, fruit, insects (caterpillars, grasshoppers, crickets, beetles and their larvae, and ants), vertebrates (toads, frogs, the eggs and chicks of ducks and songbirds, mice, smaller ground squirrels, and small rabbits), and carrion.
Tropical ground squirrels, found in the forests of Southeast Asia, also demonstrate diverse diets, generally including a greater percentage of arthropods than that of nontropical ground squirrels. The shrew-faced ground squirrel is highly specialized to eat earthworms and insects with its greatly elongated snout, long tongue, and weak incisor teeth. The three-striped ground squirrel eats fruit, roots, and insects, while plain long-nosed ground squirrels consume fruit, insects, and earthworms.
Diet in Desert Environments
In arid environments like the Sonoran Desert, ground squirrels have adapted to utilize available resources. These ground dwellers, well-equipped for digging with their strong claws and low-set ears, spend their days foraging and sunning when temperatures are moderate.
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The Harris’ antelope squirrel, found in rocky desert habitats, consumes less green vegetation and relies more on the fruits of cholla, prickly pear, and barrel cacti, as well as seeds, mesquite beans, insects, and occasionally, mice. These squirrels actively seek out seeds by sniffing the ground and digging them up, often leaving shallow divots as evidence of their activity. They even climb barrel cacti to reach the fruit, despite the spines.
The round-tailed ground squirrel, typically found on lower alluvial fans or open, flat valley areas, depends on succulent green vegetation, such as new spring wildflowers, cactus flowers and fruit, mesquite leaves, grasses, and ocotillo flowers. They also consume seeds and will take advantage of carrion, including roadkill of their own species. They usually don’t have to venture far from their burrows, finding enough grass seed, cacti, and vegetation nearby to satisfy their needs.
Rock squirrels, adaptable to various habitats including rocky outcrops and suburban lots, forage on the ground but also climb trees. They often climb into mesquites, willows, and ocotillos to feed on tender new growth, and they also climb flower stalks of agaves to feed on the tender tips.
Water Acquisition and Food Storage
Ground squirrels, particularly those in arid environments, rarely drink water, instead relying on the water content of their food. Thirteen-lined ground squirrels cache large quantities of seeds and grass, which they may consume during periods of bad weather or when other food is scarce. However, they never cache meat.
Seasonal Variations and Feeding Preferences
Ground squirrel diets are influenced by seasonal availability and feeding preferences. In spring, ground squirrels often prefer fresh greens over seeds and nuts. However, as natural grasses dry and wither, they actively forage for seeds.
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The California ground squirrel prefers to forage for food in the early morning or late afternoon/early evening to avoid the day's heat. In some crop situations, especially nut crops, squirrels may prefer the crop to the point where they will not eat any bait. In irrigated crops or landscape areas, squirrel feeding preferences are influenced by what food is available.
Social Behavior and Foraging
Some ground squirrel species, like the round-tailed ground squirrel, are social animals, living in small colonies. Round-taileds often stand on their hind legs trying to get a better view as they watch for their many predators. Because they’re very dependent on succulent vegetation for moisture, these squirrels estivate for a few weeks during the summer drought, until the summer rainy season again brings new growth.
Dormancy and Activity Patterns
Ground squirrels exhibit various dormancy and activity patterns depending on their species and environment. The round-tailed ground squirrel hibernates in winter in most of its range and estivates during the summer drought. Rock squirrels retreat to their burrow during cold winter periods, though scientists doubt that it actually hibernates. The little Harris’ antelope squirrel is active all year. The Columbian ground squirrel hibernates seven or eight months out of the year. It may begin hibernating as early as July. It has a special hibernation chamber in its burrow that is sealed off from the rest of the burrow with a plug of dirt.
Tropical ground squirrels are active all year and do not store food.
Evolutionary Relationships and Dietary Adaptations
Ground squirrels belong to the subfamily Sciurinae, which includes tree squirrels and chipmunks. Atlantoxerus, Xerus, and Spermophilopsis are closely related within this subfamily, as are Ammospermophilus and Spermophilus, which are classified in a subgroup within Sciurinae that includes marmots and prairie dogs.
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As foragers, squirrels are well-adapted to find sparsely dispersed food, one seed at a time. Once squirrels have had their fill, they will collect food in their cheek pouches and take it back to the nest to form a cache for later use. Squirrels tend to forage close to their burrow, although they will travel for desirable foods.