Squirrel Migration
By 
Even people who love squirrels might have been unnerved at what Philo Romayne Hoy, a doctor and amateur naturalist in Racine, Wis., witnessed in the autumn of 1842: thousands of squirrels scurrying across the landscape in an unbroken wave.
On they came, day after day, a great, unrelenting tide of Sciurus carolinensis: the Eastern gray squirrel. Hoy saw a similar spectacle in 1847, 1852 and again in 1857.
He wasn’t alone. The mass movement of squirrels across different portions of North America is noted in the journals of hunters, explorers, farmers and others. Every few years, thousands upon thousands of Eastern gray squirrels moved in a roughly southeasterly direction, usually in the fall. They surged through forests, their natural habitat, and into prairies, an unnatural one. They tore through cornfields like earthbound locusts, making the stalks pulsate as if buffeted by a strong wind.
Water was no deterrent. Great furry armadas swam across the Ohio (1819), the Niagara (1866), the Mississippi (1881) and other rivers, arriving bedraggled and exhausted at the far shore, where they were easy prey for hungry animals astounded at the sudden, sodden bounty.
In 1920, a wildlife writer named Ernest Thompson Seton tried to quantify the phenomenon, basing his calculations on P.R. Hoy’s account of the 1842 onslaught.
Hoy had reported that it took a month for the squirrel army to pass. Seton put the speed of the squirrels at five miles a day. He estimated how far Hoy could see at any one time and thus how many squirrels would have been in Hoy’s field of vision.
Squirrels no longer do this, though they hardly seem to be struggling to adapt to human domination of their environment. Maybe it’s just easier not to? But the idea of seeing a mass squirrel migration sort of splits the difference between fascination and nightmare.