What is Migration?

The word “migration” has a lot of meanings. For thousands of years, Indigenous people have “followed the seasons” as they harvest plants and animals across the landscape, developing an intimate knowledge of areas and resources. You could have a Great Grandpa Axel, who traveled from Sweden to the United States in 1913, looking for work and a new life. Perhaps, you and your sister escaped to another country as young children with your parents, fleeing your home? Or you might know a “Grandma Jean” who spends summers in Wisconsin and migrates to Arizona for winter as a “snowbird.”

Like people around the world,
many different animals migrate too

What separates animal migration from other types of movement, is it happens seasonally and involves a return journey. A wide variety of animals migrate including mammals, birds, fish, insects, reptiles and more, and they can travel by land, water, or air. Some migrations can be a relatively short distance, spotted salamanders may travel less than 1,000 feet to their egg laying pools of water. Others, like the arctic tern, travel the length of the globe from Antarctica to their Arctic breeding grounds and back, 25,000 miles per year!

 

NPS Illustration, Base map by Tom Patterson

 

How do Animals Know to Migrate?

One truly remarkable thing about migration is how animals know where they are going. Much like human children, deer, elk, and even humpback whale calves learn a lot from their moms, including what to eat and where to migrate! Many birds navigate using the sun or stars position in the sky. Other birds, sea turtles, or salamanders are guided by the Earth’s magnetic field along their journey. Meanwhile, wildebeest or salmon use their sense of smell to follow the rain or return to the very same stream where they were born.

Migration is happening all around us. From huge herds of caribou in Alaska to a million Sandhill Cranes crossing through Nebraska, these journeys are a spectacular phenomenon. Perhaps there is an animal migration happening near your home? Or in your own family’s history? Or you, too, could plan a journey, guided by your senses, seeking out the resources you need to thrive.

 

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Egg-cellent Migrations

Migration can take many forms. Green, Loggerhead, Kemp’s Ridley, Hawksbill, and Leatherback sea turtles make annual trips to lay their eggs on sandy beaches around the world, including many coastal national parks, such as Dry Tortugas National Park, Padre Island National Seashore, and Cape Hatteras National Seashore.

These reptiles, some weighing up to 2,000 pounds, spend most of their lives at sea. Female sea turtles, after reaching sexual maturity at over 30 years old, return to land at night to lay around 100 eggs in a clutch before returning to the ocean.

“When the little dudes are just eggs we leave them on a beach to hatch, and coo-coo-cachoo, they find their way back to the big ol’ blue.”

– Crush, Finding Nemo, 2003

The eggs hatch after approximately 60 days. These hatchlings use the slope of the beach and reflections of moon and starlight on the water to guide them to the sea, where they use waves and magnetic orientation to reach their seaweed “nurseries”, home for the next 10 years. This challenging journey means only one in 1,000 to 10,000 hatchlings survive.

All five species of sea turtle are listed as either Endangered or Threatened by the Endangered Species Act. Many human activities threaten sea turtle survival, including the loss of nesting habitat due to coastal development, entanglement in fishing gear, being hit by boats, disturbance of nesting beaches, pollution in the ocean, and harvesting of eggs and adults for food and commercial purposes. Fortunately, by increasing awareness of migration and its impacts, we can take steps to mitigate these threats.

 

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Keep Humming Along

Tiny hummingbirds, some weighing a little more than a penny, undertake a remarkable migration each year. Most hummingbirds spend their winters in Central America or Mexico. Each spring, they fly north to breed as the temperature gets warmer and make their return journey in August or September.

A hummingbird’s heart may beat 1,260 times a minute and flap its wings 15 to 80 times per second while migrating. These tiny engines need a lot of energy. Like any road trip, to prepare for this journey, they need to stock up on supplies and may gain between 25-40% of their body weight before starting their migration.

Instinct tells them when it is time to leave, and they will follow the same flight path throughout their lives. Typically flying alone, though hummingbirds may gather in groups when crossing large bodies of water. Most days include stops to resupply, eating flower nectar and insects over the course of a 20-mile day. Some remarkable birds crossing between Florida and the Yucatan in Mexico will fly 500 miles nonstop in 18-22 hours!

Like many birds, hummingbird’s habitat is vulnerable across their migration range. We can help by planting native flowers or plants which are appealing to hummingbirds and avoid using chemicals which may harm birds, insects, or other wildlife.

 

Not all animals migrate

In Grand Teton National Park, red foxes are well adapted to spend the entire year here, from warm summers to cold, snowy winters. In summer, they will shed their guard hairs and can appear almost black, at times. Whereas in winter, that thick fur and bushy tail helps to keep them warm when temperatures plummet. Red foxes are skilled hunters as well, with a great sense of smell and hearing to track prey under the snow.

While these adaptations help red foxes stay in the same area year-round, many animals need to move from one habitat to another as they look for resources to survive. What sort of things do animals need? Much like people or red foxes, they need food, water, shelter, a place to reproduce, and perhaps, like Grandma Jean, just nicer weather? Migrating animals may not have a particular adaptation to remain but are well adapted to travel and find these important resources.

 

Left image
Fox and kit in summer

Right image
Fox on top of the snow