I just realized this post was in my “draft” box. It was written nearly two years ago, but the message is still timely, so enjoy….
Since I just moved from one state to another I started thinking about animal migrations. Why do they do it? What motivates them to expend the time and energy required for a long distance migration? The answers are both obvious and subtle.
First of all, what is a migration? The Natural History Museum of the United Kingdom says it is “a journey with a clear purpose from one area to another, often following a well-defined route to a familiar destination, and often at a specific time or season.” However, they go on to say that there is no universally accepted definition and it’s not always easy to tell a true migration from something else. We tend to think of birds flying south for the winter as a migration, but there are many other species that migrate as well.
Migration is usually fueled by the search for food. Birds fly south to find insects, fruits and seeds that they can’t find in their more northerly habitats during the winter and caribou migrate across the tundra searching for fresh grasses. But animals may migrate for a host of other reasons including to find shelter, like the monarch butterflies flying to Mexico, searching for a mate, like male sperm whales, or fleeing an overcrowded habitat, like Norway lemmings. Even some human cultures still migrate to find fresh food for their livestock and avoid harsh climate conditions.
We tend to think of migration as a north-south journey but that isn’t always the case. Migration can occur when an animal travels up and down a mountain at certain times of the year, called altitudinal migration, as evidenced by elk and bighorn sheep in the Rocky Mountains. They spend the winters below the timberline where there is food for them to eat, and slowly advance back up the mountain as snow melts, in order to get further away from predators. Scientists believe this type of migration will take place more often in the future as the climate changes, forcing cold-loving species to move higher up into the mountains until they can go no further. Migration can also occur when aquatic animals move up and down in the water column, called diel vertical migration. Lanternfish are one species that does this. They travel from their deep habitats to shallower water at night in order to locate prey.
Why don’t animals just live somewhere with enough food and ideal habitats so they don’t have to migrate? Just imagine if all the world’s animal species lived in those rare, ideal habitats. It would be quite overcrowded, with diseases, competition, and fighting running rampant. Animals have evolved to live in certain habitats, eat certain foods, and migrate if they need to, in order to minimize competition as much as possible and ensure the continued survival of the species. Migration is one essential tool for doing so.