In 1968, 20 million squirrels suddenly began migrating across America. The mass exodus confused scientists but the answer was in what happened a year before

In the autumn of 1968, an unusual sight was seen across the eastern United States when thousands of grey squirrels poured out of forests, crossed busy highways and attempted to swim across lakes and rivers. Many drowned or were killed by vehicles, leaving wildlife officials struggling to understand what had triggered this sudden movement among them.

Some estimates put the number of squirrels involved at 20 million and despite the scale of the event, the animals were not moving because of an unknown disease or an unexplained change in behaviour. The investigation eventually pointed to a problem with the forests they depended on for food.

Strange movement leaves scientists puzzled

According to Smithsonian magazine, reports of squirrels appearing in unusual places started to come from several states. In North Carolina, animals were seen swimming across reservoirs, while motorists encountered large numbers of dead squirrels along roads. Some wildlife officers reported collecting dead animals at a rate of roughly one per mile in affected areas.


The movement was not limited to North Carolina. In New York, conservation officials collected 122 squirrel specimens from highways near Albany and received reports of squirrels drowning in the Hudson River.

Newspapers covered the phenomenon as wildlife authorities tried to understand why so many animals were leaving their usual habitats. Some people assumed the squirrels were starving and began sending boxes of acorns and hickory nuts to affected areas. Grocery stores also encouraged shoppers to feed them. However, the scale of the movement needed a scientific investigation.

Squirrel expert was brought in

The Smithsonian Institution's Center for Short-Lived Phenomena, established in 1968, was alerted to the unusual reports. The centre had been created to collect information about rare and sudden events that scientists might otherwise miss, from volcanic activity to unusual animal movements.

It contacted Vagn Flyger, a zoologist at the University of Maryland who was studying squirrels. Flyger travelled to North Carolina and established a makeshift laboratory in a motel room in Boone, where he examined squirrel specimens with help from other researchers.

The investigation did not uncover any unusual findings in the animals' bodies. Nor was there clear evidence that they were all travelling in one particular direction. Instead, Flyger's observations and talks with people in the affected areas pointed towards changing food supplies.

Bumper crop may have triggered the exodus

According to Flyger, the previous year had produced an unusually large crop of acorns. More food meant more squirrels survived and bred, and so their numbers grew exponentially.

The situation changed in 1968, when the supply of nuts was much poorer. By autumn, young squirrels from the year's first litter were leaving their nests, adding to the demand for food.

With too many animals competing for fewer resources, squirrels began moving out in search of better feeding grounds. The apparent mass migration was therefore an attempt to survive, rather than a coordinated journey towards a particular destination.

Wildlife experts have since described such movements as emigration; animals leaving an area because local conditions have become unfavourable.

The 1968 episode was not the first recorded instance of squirrels moving in huge numbers. Historical accounts describe similar movements in the 19th century, including an exodus in Texas in 1857 after a severe cold snap damaged vegetation and nut-bearing trees.