After billions of years of evolution, the animal kingdom has developed a few tactics for dealing with the Earth’s fluctuating seasons. Some species prefer the homebody method of hunkering down through the winter months and entering an almost death-like state of hibernation. Other animals take a more travel-centric approach and head for warmer climates as the mercury falls. Some of these migrations go mostly unseen by human eyes, while others fill the skies with dazzling feathers or shake the ground with thunderous hooves.
These seven facts about the world’s most amazing migrations showcase how some of Earth’s most incredible creatures swim, fly, and stampede throughout the world.
Arctic Terns Are the World’s Most Impressive Migratory Fliers
The name “Arctic tern” is a bit of a misnomer. Although this well-traveled bird does spend the summer months in the Arctic, it also spends equal time in the Antarctic. That’s because twice a year, the Arctic tern (Sterna paradisaea) flies from one freezing landscape to the other, making the longest migration — more than 19,000 miles — of any known animal. The tern undertakes this incredible journey, which lasts several months, because it relies on summer sunlight to illuminate fish in the sea and insects on land. That means the dark, dayless winters in these cold climates are a big no-go. Fortunately, the Arctic tern can eat and sleep while gliding on the ocean breeze, and if it didn’t need to hunt for food, it could probably fly upwards of 1,000 miles a day.
For the Monarch Butterfly, Migrations Are Multigenerational
In the early days of spring, the monarch butterfly (Danaus plexippus plexippus) leaves its overwintering location among the branches of oyamel firs in central Mexico and begins a 3,000-mile migration to the northern U.S. and Canada. Part of what makes this journey so spectacular is that it’s a multigenerational one. Because the butterfly only lives for about four weeks, it takes four generations for the creature to get from point A to point B. (There’s one exception: The “super generation” that lives eight times longer during the laborious return trip south.) The monarch is the only species of butterfly known to undergo such an extensive migration.
The Wildebeest’s Annual Journey Is Known as the “Great Migration”
Every year, 1.5 million wildebeest, also known as gnu, along with some 400,000 zebras and nearly as many gazelles, travel in a roughly 500-mile loop in the Serengeti plains in search of seasonal rains and grazing grounds. At the beginning of the year, the wildebeest gather at the edge of the Serengeti and all give birth in the same month. Within two days, calves are able to keep up with their parents, and soon the massive pack begins a journey scientists call the “Great Migration.” The pack travels north and eventually arrives in the well-watered Kenya savannah known as Masai Mara, where they stay from July until October. The smell of November’s rains then signals to this mass of animal life that it’s time to head southward and return to the Serengeti.
Every Fall, Some 10 Million Fruit Bats Migrate in Southern Africa
Although millions of stampeding zebras and wildebeest are an impressive sight, in nearby Zambia, the straw-colored fruit bat (Eidolon helvum), part of a genus of bats known as flying foxes, takes the idea of strength in numbers to a whole new level. Between October and December, upwards of 10 million of these bats descend on Kasanka National Park to feast on the area’s plentiful fruit trees, and in turn spread seeds throughout the plains and savannahs of southern Africa as the bats return home to the Congo rainforest. This vital and mysterious migration — considered the largest migration of any mammal in the world — is under threat from deforestation and poaching, but conservation groups are hard at work protecting this bat species.
Salmon Migration Is the Animal Kingdom’s Most Grueling
The salmon run, one of nature’s most wondrous migrations, takes place in the fall months as the persistent family of fish attempts to return to its spawning grounds. Nearly all salmon (Atlantic, Pacific, et al.) are anadromous, meaning they migrate from saltwater oceans to freshwater streams to spawn; their eggs can only survive in these freshwater locations. Salmon must not only swim upstream against the current, but also jump over obstacles, like falls, by launching their bodies through the air. Although structures such as dams or weirs often have fish ladders to aid salmon in their journey, human-made obstacles have negatively impacted salmon numbers. This is an especially big problem in the Pacific Northwest, where salmon are a keystone species, meaning their ecological impact outpaces their overall size. In 2022, Oregon underwent the world’s largest dam removal to protect this vulnerable species.
The Gray Whale Undergoes the Longest Migration of Any Mammal
In late spring, the gray whale (Eschrichtius robustus) returns to the Bering and Chukchi seas off Alaska after completing a monumental 12,000-mile round-trip journey, the longest of any mammal on Earth. Although not as gargantuan as a blue whale, the gray whale stretches some 45 feet long (and can weigh more than 72,000 pounds), and every year migrates that massive bulk southward to the warm lagoons of Southern California and Baja, Mexico. The trip takes about two or three months each way, and the first to arrive in these warm waters are pregnant mothers looking to use the lagoons as protection for their young calves. Around late March to late April, the gray whale makes the journey back toward Alaska — late enough to make sure the newborn whales can make the trip. The U.S.’s National Oceanic and Atmospheric Administration estimates that some 24,000 gray whales make this journey every year.
One of the World’s Most Amazing Migrations Happens Every Day
Most people think of migrations as a natural rhythm dictated by the seasons, but the largest migration in the world actually happens every single day. At night, trillions of sea creatures known as zooplankton — krill, salps, fish larvae, and microscopic organisms — travel to the ocean’s surface to feed on phytoplankton. Although this journey might be only 1,000 feet in some cases, for a quarter-inch fish larva, the speed of the trip is roughly equivalent to a human swimming 50 miles in an hour. These animals go deeper into the waters during the daytime to avoid predators, though the nightly journey to the surface isn’t exactly safe either. Although the trek was first documented in the 1800s, scientists are still trying to piece together the inner workings of this daily migration that happens almost completely out of sight.