If you are like me and have just cancelled your Thanksgiving travel plans, you may be feeling an almost irresistible pull towards a place or a group of people that you are always with at this time of year.
It is a feeling that was learned from many years of tradition, but there is also some primordial instinct that draws you to be at a given place, a given time. This feeling is probably as close as most non-nomadic humans come to the migratory instinct that directs some birds, mammals, insects, fish and reptiles to move from one place to another.
In nature, migration is not such an unusual thing. Lots of organisms do it. What is amazing is the consistency which individual species will display when they migrate.
Perhaps the most famous, thanks to crooners like Pat Boone or the Ink Spots, are the swallows that make a 6,000 mile journey from Argentina to San Juan Capistrano, California and manage to arrive on the same day every year (March 19, St. Joseph’s Day)!
If you have watched The Lion King, you know that 1.8 million wildebeest migrate annually from the Serengeti, Tanzania to Masai Mara, Kenya in what is known as one of the 7 Wonders of the Natural World. The Arctic Tern is considered the long-distance champ, flying 44,000 miles each way between the Arctic and the Falkland Islands near Antarctica.
In its lifetime, an average Arctic Tern would fly about 1,491,300 miles. One of shortest migrations is the annual crossing of La Rue Road in the Shawnee National Forest by hundreds of snakes and other reptiles. One side of the road is swamp, the other side is limestone cliff and the migration of these determined reptiles requires road closures for four months each year to protect the animals from cars.
Usually migration, including by humans, is carried out due to changing temperatures or seasonal reduction in food supplies. In mountainous places around the world, like the Appalachians, people have traditionally moved their livestock up to higher meadows in the summer and down to lower pastures for winter.
This is the same concept as migration.
There is a lot of speculation about how a species knows when and where to migrate. Is it genetic? Do they learn the route when young and remember it? Do they have magnetic sensors in their brains that show them north and south? Do they just ride the air and water currents as the path of least resistance?
Scientists have found some species that seem to fit into each of those explanations, but there are still a lot of unanswered questions.
Monarch butterflies are a mysterious species. They spend the spring and summer months in Canada and the northern U.S.A. Here there will be up to four generations in a year that go through the whole life cycle without moving significantly north or south. But the last generation of the year, the generation that emerges from cocoons just before temperatures go down to freezing will migrate up to 3,000 miles to a forest in central Mexico.
These same individuals will live long enough to return a few hundred miles north, lay their eggs, and start the process again. Each generation will move slightly further north during its life cycle, following the milkweed growth, until it is time for a new generation to migrate.
Here in eastern Tennessee, we await the annual arrival from Canada of the Sandhill Cranes to the Hiawassee Wildlife Refuge. Sprinkled in among the thousands of grey Sandhill Cranes, you might be lucky enough to spy a white Whooping Crane. The population of Whooping Cranes in North America was down to 20 individuals in the 1940s. After an intensive breeding program, the population is up to about 600 birds today, but it is still considered endangered.
Scientists had to teach Whooping Cranes how to migrate successfully. They first taught the young birds to follow an ultralight plane, which led them along their migration route. This route coincides with the Sandhill route, so now Whooping Cranes can make the perilous journey in the relative security of a large flock of Sandhill Cranes.
There are a lot of dangers along the way in any migration. Cars, boats and even airplanes kill a lot of animals every year. Windmills are a relatively new phenomena that flying birds, insects and bats have to learn to evade.
Predators, every bit as programmed to the timing of migrations as the migrators themselves, are waiting for the flocks and herds to pass by: crocodiles in the Mara River; eagles and hawks along the Tennessee River. Many animals begin to migrate as soon as their young are strong enough to make the journey, making them more susceptible to becoming someone’s supper.
Changing land use is a threat that migrating animals cannot plan for. Deforestation in the Amazon, new shopping malls covering up fields in North America, dams in rivers where salmon spawn and swamp drainage in developing countries all create problems for animals that are depending on traditional feeding, resting and breeding grounds to make their annual pilgrimage.
TWRA tries to help by planting corn and millet in the wildlife refuge for the cranes. Many people plant milkweed for the butterflies or put out feeders for the birds.
Some species migrate through several countries. Wars as well as unmanaged hunting in some countries result in many individuals dying along the way. Hurricanes and droughts also impact survival.
When we plan a trip, or cancel a trip, we have information to help us make the decision. We know that COVID is spiking or that a hurricane is about to hit or that Aunt Gussie just sold her house and can no longer offer a guest room.
Using that information, we can make the best decision for the trip. Even though we yearn to travel, we can decide to stay in place.
With migratory animals, they use their instinct and their experience, but have no way of knowing what new threats may lie ahead. When they start their journey, they are following a pattern that has been in place for eons of time. And yet, despite the threats along their way, without GPS or internet, most will survive, arrive at their destination and return.
Migration truly is one of the marvels and mysteries of our natural world.
Kathryn Hunter is from McMinn County and holds a bachelor’s degree in Forest Resource Management from the University of Idaho and a Master of Forestry from Yale University.