One fall day in 1856, a family of Eastern gray squirrels in rural New York uncurled from a cozy nest in a chestnut tree, looked around, and joined half a billion other squirrels on a multi-state walkabout. Waves of fur, claws, and sharp incisors swarmed like locusts in squirrel armies that could be up to 150 miles long, “devouring on their way everything that is suited to their taste,” wrote John Bachman, a 19th-century naturalist.

Walls of Sciurus carolinensis pulsing across the landscape befuddled naturalists and frustrated farmers, but these movements were a survival strategy, says John Koprowski, the dean of the Haub School of Environment and Natural Resources at the University of Wyoming and a longtime squirrel expert.

“Squirrels have an amazing sense of smell. They often find fruiting trees, trees with good crops, from miles away,” Koprowski says. “When you had continuous forests with acorns or chestnuts that are all blooming or fruiting at the same time or producing seed crops, that had to be a pretty powerful smell moving through the forest.”

The strategy worked. By taking these mass rodent odysseys, squirrels settled new areas, found higher-quality munchies, and, in turn, made more squirrels. At one point, naturalist Ernest Thompson Seton estimates Eastern gray squirrels likely numbered in the billions.

This is almost impossible to imagine today. But this emigration wasn’t the only odd feat of dispersal by wild animals. The now-extinct Rocky Mountain locusts once migrated across the country in waves. Passenger pigeons, also extinct, moved in flocks so thick they darkened the sky. Jackrabbits — still abundant today but more sedentary — once moved en masse, ripping through crops so severely during the Dust Bowl that people drove them into pens and killed them by the thousands.

Some species, especially birds and some large mammals like deer and elk, still make pilgrimages. But many more, including the Eastern gray squirrel, have lost their ability to move long distances, lacking large connected forests and unable to navigate through industrial parks and parking lots, over six-lane interstates or subdivisions.

“We don’t have millions of animals in those places anymore,” Koprowski says. “They’re giving us an early warning that these aren’t functioning the way they have historically, in the ways that animals have evolved to be using these spaces.”

And that warning is becoming more dire. A 2024 United Nations Report found that 44 percent of the world’s migratory species are declining, a result of overhunting paired with habitat destruction largely due to agriculture, sprawling housing and commercial development, pollution, and, increasingly, climate change.

Yet as wildlife lose the freedom to move, biologists say the ability to shift from one place to another to find food or escape threats will become even more necessary as our planet continues to change.

There are still some incredible feats of migration that are hanging on. These epic tours serve as a reminder that not all is lost.

Arctic hares that run ultras

North of those once-abundant Eastern forests with their once-abundant Eastern squirrels, there’s another small mammal with a surprising penchant for long-distance quests: the Arctic hare.

Protected by a special adaptation — a dazzling coat of thick fur that turns white in the winter and thinner and blue-gray or brownish in spring and summer to camouflage to its surroundings — the Arctic hare can survive frigid temperatures. But when the thermometer in the polar desert dips to below negative 40 degrees Fahrenheit, they begin hopping southwest — sometimes for nearly 200 miles.

This marathon feat was a surprise to scientists who discovered the journeys in 2019.

Previously, researchers largely believed Arctic hares were “sedentary species with little dispersal capacity.” Researchers at the University of Quebec at Rimouski knew hares could travel quickly — up to 40 miles per hour — but they wanted to see just how far they could go.

They were stunned to discover that the creatures regularly traveled hundreds of miles — likely headed for warmer pastures with more abundant plants and glacial meltwater, says Ludovic Landry-Ducharme, a PhD student at the University of Quebec at Rimouski who is continuing the research.

The Canadian researchers published their work in the journal Nature and underscored that climate change may well disrupt these patterns as snow comes later and spring melts come earlier, shifting where and when — and how abundantly — important plants grow.

The propensity to look for good food and escape bad weather conditions is one of wildlife’s oldest adaptations and most often documented in more visible species like mule deer in the American West, wildebeest in Sub-Saharan Africa, and caribou in northern Canada. Indigenous people long knew wildlife moved with the seasons, and many followed those movements, taking advantage of the weather and trailing along with a consistent food source.

But it was only more recently that researchers with modern satellite technology began to map exactly where the wildlife moved. Those results made headlines with stories of mule deer faithfully following the same 150- or even 250-mile migrations up and over mountain ranges.

Many animals — from Arctic hares to mule deer — use what researchers call stopover points. These are areas along the way where species can rest, take a breather, and eat.

Wyoming migration researcher Hall Sawyer once described stopovers as pit stops on a long interstate road trip. Drivers who stop for gas, a cup of coffee, and a meal make better decisions and arrive better rested than those who power through.

For animals, it’s no different. Their cross-country trips can look meandering and erratic, but according to scientists, they are critical and increasingly threatened by everything from highways and fences to drought, fires, and floods worsened by climate change to energy developments, subdivisions, and agricultural fields.

A newt’s year (or seven) of self-discovery

Anyone who has gone for a walk through a pocket of Eastern forest has likely spotted a burnt-orange eastern newt. Next time you see one, thank it not only for its mosquito-killing capabilities but also wish it well on what amphibian researcher JJ Apodaca likens to its Rumspringa.

When a newt enters its eft stage, it experiences a fundamental physiological change. The newt starts its life journey in a pond looking like an olive salamander with feathery gills and a narrow tail before it crawls out onto land, turns orange, and swaps out its gills for a set of lungs as an eft. Once on land, the newt sets out for parts unknown, spending two to even seven years meandering — sometimes for miles — on its tiny legs to what it surely considers faraway lands. After years of roaming, it returns to a pond or wetland, dives back into the water, and looks for a mate.

Those eft walkabouts are a critical time to look for the best food while the juvenile newt grows and matures. And the more fragmented their habitat, the less cover they can find on leafy, forested floors and the higher the chance for a run-in with a car tire.

They’re not the only amphibians that require room to roam. Instead of skittering horizontally, the green salamander looks upward for greener pastures. The salamanders climb trees for better food (and also likely to avoid becoming food).

But as humans continue to chop down some trees — and pests and disease targets other trees — fewer and fewer salamanders remain.

The ability to seek out new territory isn’t just critical for a species’ overall population, but will become even more important as habitat shrinks and the climate changes.

In March 2018, a female Arctic fox wearing a tracking collar traveled from a research site on a Norwegian archipelago to the Canadian Ellesmere Island, paddling more than 2,700 miles from start to finish in the span of just four months. And she’s certainly not the only one. According to a study by Eva Fuglei, a Norwegian Polar Institute researcher, Arctic foxes have the ability to bridge continents, have crossed ice sheets, and have connected to distant populations — keeping their genetics spanning generations robust.

But as sea ice melts, those populations will likely become isolated.

The problem with animal islands

Eastern gray squirrels continued their periodic decampments, fewer and fewer each year, until naturalists reported some of the last major ones in the 1960s. Humans’ desire for timber and space for parking lots and shopping centers eventually proved too much for even the most industrious squirrel, and the long emigrations eventually ended.

Today, a much smaller relative population of Eastern grays live in piecemeal habitat, islands locked in by roads or development.

Wildlife, even those as small as salamanders or as big as wildebeests, don’t function as well on islands as they do in connected landscapes. A 1987 paper published in the journal Nature showed that more species went extinct in 14 western American national parks than were naturally reestablished there. The island effect, as it’s called, shows that even if animals live in protected areas like national parks, those parks are often too small.

“The effect of habitat loss and fragmentation on populations, going from intact to fragmented, is as close as we have to a golden rule in conservation,” says Matthew Kauffman, Wyoming Cooperative Fish and Wildlife Research Unit leader and longtime migration researcher. “Populations will be less robust when you go from a large, intact habitat to the same habitat but fragmented, where animals can’t move.”

Fortunately, in recent years, there have been promising moves to reconnect habitat, even within an increasingly fragmented landscape.

Across the country, states, nonprofits, and the federal government have worked together to install wildlife crossings — over- and underpasses that provide safe passage for everything from salamanders to mountain lions from the forests of Massachusetts to the multi-lane interstates of Southern California.

Apodaca’s organization, the Amphibian and Reptile Conservancy, recently completed work on a culvert under a highway to usher the increasingly endangered bog turtle from one side to another, giving the creature access to varied habitat it would otherwise seek by perilously waddling across the road.

States like Wyoming and Colorado are using maps of deer, elk, and pronghorn migrations to tweak locations of oil and gas development or potentially even modify subdivisions. Wildlife managers also now understand the importance of those long-distance pit stops to wildlife abundance.

Conservationists also praised efforts like President Joe Biden’s plan to conserve 30 percent of the country’s land, freshwater, and ocean by 2030 as a way to maintain critical habitat and migration pathways. The future of those efforts under the incoming Trump administration, however, remains murky.

Eastern North America may never again see swarms of half a billion squirrels skittering through forests en route to lush acorn crops, but for other species, researchers say, it’s not too late.