The American Red Squirrel Is Small, Territorial and Aggressive

By: Mark Mancini  | 

red squirrel
Despite their small size, red squirrels (Tamiasciurus hudsonicus) are known to be super aggressive if they feel threatened. Björn Lauer/Getty Images

The American red squirrel (Tamiasciurus hudsonicus) comes as advertised. Somewhat. Found in the Rocky Mountains, parts of Alaska, southern and central Canada, the Great Lakes region and the northeastern United States, this rodent is as American (and Canadian) as it gets.

True to its common name, the animal's got some rusty red fur. So far, so predictable.

Yet the American red squirrel does certain things that may surprise you. We're talking nest-raiding, bird-eating and premeditated infanticide. Yikes.

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Squirrel Power

Zoologists have tallied up more than 200 distinct squirrel species, from the African pygmy squirrel to the beautiful Indian giant squirrel. If you live in the eastern or Midwestern U.S., then you're probably most familiar with Sciurus carolinensis, the eastern gray squirrel.

While all-white and all-black individuals aren't unheard of, these squirrels tend to be gray-furred with light underbellies.

Contrast this with the American red squirrel. It's got a light underbelly as well, but we think you'll agree the backside is more vibrant. Red-brown to red-gray fur covers the head, tail and back — along with most of the available skin on all four legs.

You might notice black stripes running down each flank. When present, these lines form a boundary between some of the darker hairs on top and the lighter ones coating the belly. Like the eastern gray, the American red squirrel has a ring of white fur around both eyes.

Eastern gray squirrels grow about 15 to 20 inches (38 to 51 centimeters) long. American red squirrels are a little over half that size, measuring between 11 and 14 inches (28 and 36 centimeters) from twitching snout to bushy tail.

But don't mistake Tamiasciurus hudsonicus for some timid little pushover. On the contrary: This is one aggressive rodent.

red squirrel
Red squirrels are quite vocal and use barks and other sounds to raise alarm when they see danger.
Kim MacKay/Getty Images

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Seeing Red

Red squirrels are notorious for raiding bird-feeders. In the process, they won't hesitate to chase away eastern grays — despite the size disadvantage.

Same-species encounters can also get testy. By and large, red squirrels live alone. At just 9 to 11 weeks old, they'll begin to stake out territories covering up to 8 full acres (3.3 hectares).

Not all territories are fully private. Red squirrels living in New York State have been known to share portions of their stomping grounds with the neighbors. And a mother squirrel in poor health might surrender real estate to her offspring.

Nevertheless, in the vast majority of cases, American red squirrels do not tolerate intruders. Like a lot of mammals, the squirrels use scents to help mark their territories. Uninvited guests are met with a hostile buzzing noise. Sometimes, the "owner" of the turf will shake its tail and stamp its little feet to make itself more threatening.

The squirrels are quite vocal around predators, too. Barks and other sounds act as alarm calls, raised when they see a dangerous carnivore. Tamiasciurus hudsonicus has enemies to spare; foxes, wolves, weasels, lynx, coyotes, crows, birds of prey and timber rattlesnakes all hunt this squirrel in the wild.

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"Midden" Their Own Business

Granted, red squirrels do their fair share of hunting as well.

Young birds sometimes fall prey to the tree-climbing rodents. So do unhatched bird eggs. And insects. Heck, if you can believe it, red squirrels will devour baby snowshoe hares when the chance arises.

Mushrooms are a favorite treat. Sometimes, these require a bit of prep work; red squirrels have been known to pluck shrooms at ground level and then hang them out to dry on tree branches before chowing down.

Sap, tree bark, fruits and flowers factor into the red squirrel's diet as well. But seeds are their main source of food.

The species typically lives in coniferous and deciduous forests. In such places, it's easy to find conifer cones loaded with rodent-friendly seeds. So the red squirrels living there tend to keep lots of these cones in storage spots called "middens." A midden can take the form of an underground hiding spot — or a heap of cones lying beside some tree trunk.

American red squirrels are both a blessing and a curse for the trees that sustain them. In the "negative" column, they can seriously damage trees by stripping their bark away. Overharvesting cones is another potential problem.

Yet the squirrels are also really good at spreading those cones around. They don't always recover middens after building them up, which leaves the cone seeds to mature in place. Food caches are a wintertime necessity for many Tamiasciurus hudsonicus, as the species doesn't hibernate.

red squirrel
Red squirrels typically live in coniferous and deciduous forests, and one of their favorite foods is conifer cones loaded with rodent-friendly seeds.
Alina Morozova/Getty Images

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The Males Are Murderous

Ironically, bountiful harvests can spell doom for newborn red squirrels. White spruce trees produce a greater-than-average number of cones in certain years — which botanists call "mast" years.

Now during a mast year, female red squirrels are more likely to have two litters of pups instead of one. That's important because it gives male squirrels a horrifying opportunity.

In 2018, the journal Ecology published a study documenting sexually selected infanticide in American red squirrels.

Early one mast year, the authors observed several wild males slaughtering newborns fathered by their rivals. The tactic is intended to make mother squirrels reproductively available again. And it works. After a female's first litter is destroyed, a murderous male can move in and sire his own pups with her.

Funny how that never came up in the old "Screwy Squirrel" cartoons.

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