One way of coping with scarce food or bad weather is to migrate to warmer climates or areas where there are more resources available. Migrations aren’t random events and it is not only birds that ‘fly south for the winter’. Seasonal migration is not widespread among terrestrial mammals, however, mainly because walking speed is too slow in comparison to flight. More migratory animals are found in North America than anywhere else in the world.
Whales for example have the longest migrations for all mammals, moving from warm breeding grounds near the equator, to cooler feeding areas closer to the poles. Reindeer herds leave the tundra as winter approaches; mountain goats descend to below the tree line as winter sets in and lemmings have been known to have large migrations in search of new areas to live.
Wildebeest travel in huge herds across Africa in search of greener pastures and watering holes. While most animals will follow the same migratory route each year, the wildebeest may stray from previous routes if grass is growing in different or unusual places.
How do Mammals Know When to Migrate?
For some mammals migration is crucial to their survival. In some cases the mammals know when to migrate based on internal body clocks known as circadian rhythms. These body clocks affect bodily functions. Some mammals rely on photoperiod, noticing the days getting shorter based on how much daylight there is. Seasonal changes as well as other environmental changes such as a lack of food or other resources due to overcrowding or as a result of drought are indicators for many animals.
The caribou of Alaska and Canada migrate anywhere from 160-1100km (100-700 miles) twice per year. Northern fur seals migrate up to 2800km (1740 miles) in early summer to give birth and to mate. And while many bats spend winter in hibernation or daily torpor, there are four species of American bat that migrate to different areas during summer and winter.
If all the animals from the group migrate, this is referred to as complete migration. When only some go, it is called partial migration. An animal such as the mountain goat descending down the mountain to avoid the snowy peaks is demonstrating altitudinal migration.
Most mammals that migrate do so for better food, or to avoid cold weather, and also to breed and mate so as offspring have a good chance of survival in warmer areas and with an abundance of food and less predators. Migratory responses evolved most likely as a result of population pressure, due to lack of resources. It is just another survival skill to help these mammals live as best they can and produce as many viable offspring as possible.
Resource and further reading:
Hickman, Roberts, Larson & I’Anson, 2004, ‘Mammals’ in Integrated Principles of Zoology, 12th edition, ed. McGraw Hill, New York, chapter 28.
Roberta Goli - Roberta has a Bachelor of Science Degree (Zoology), has worked with animals for over 10 years and enjoys writing short stories and flash ...
