Definition of Migration
The term migration relates to the relatively long-distance movement of birds or animals or humans. The most common migration in ecology is seasonal movement. It is observed that a lot of species of birds and animals migrate from almost one hemisphere to another. It includes groups of mammals, birds, reptiles, fish, crustaceans, and insects. The reason for migration is mainly food, climate, season, or mating.
As such, migration cannot be defined in specific words but based on the general observation and habitats of migrators, and it can be summed up as follows –
"Migratory behavior is persistent and straightened out movement affected by the animal's locomotory exertions or by its active embarkation upon a vehicle. It depends on some temporary inhibition of station-keeping responses but promotes their eventual disinhibition and recurrence."
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Concepts of Migration
Persistent straight movement
Relocation of an individual on a greater scale than its average daily activities
The migration in the same species is not obligatory; however, it can be obligate in some cases while facultative in others. Within a migratory species, some individuals migrate, and some do not. When all individuals migrate, it is 'complete migration.' When some individuals migrate, and some do not, it is partial migration. When the difference between migratory and non-migratory individuals is based on age or sex, it is differential migration.
Types of Migrations in Mammals
Seasonal Migration – During the year, various species move from one habitat to another; this is seasonal migration. The inability to get the habitual climate and food forces these species to migrate to the place where it is available. These favorable conditions are dependent upon the cycle of nature, and the migratory species know where they will get it during that period of the year. This applies to birds, fishes, and animals, including mammals. Species like Pacific salmon migrate to reproduce, and many species of birds migrate because of the temperature factor.
Circadian Migration – This is observed in birds that can use circadian rhythm (CR) to control migration in both the fall and winter seasons. Both daily and annual circadian clocks are used to determine the orientation of birds in terms of time and space during their movement. The auditory and spatial memory in bird's brains that live close to the equator allows them to remember the exact destinations. They can understand the distance and time required to travel because of their timing mechanism.
Tidal Migration – As the name suggests, it is more related to the migration of aquatic animals. The tidal migration includes the movement from a few mm to thousands of kilometre. The Intertidal zone during the daily tidal cycles is the most common tidal migration. Organisms like nematodes, crabs, corals, small fish, etc., form a dense population with many nutrients. In addition, foraging of marine and bird species assists cycle movements. During high tide, larger species are found in deeper water, and during the low tide, smaller species will come up to forage as their survival is easier in shallow water.
Mammals Migration
Migratory mammals can be seen across the world. Some species like caribou are extraordinary in migrations. They show the longest terrestrial migration ever known. The migration in mammals is mainly known for its ability to carry it longer. Migratory mammals show impeccable unity while they are migrating. Caribou, as mentioned above, begin to move randomly towards the south and spend winter either in taiga or in northern forests. Each move with the local conditions and without a pattern. However, each time they travel similarly on the course.
Like humans, the animals also do many things to go through the winter. Some 'migrate' to cope up and move to warmer places. Birds mostly migrate during winter. The migration distance may be short, but the purpose remains the same. The animals that migrate during winter include bats, caribou, and elk. Apart from that, fish and insects also migrate during the winter. Moths and butterflies cover quite a long distance to migrate between Canada and the US.
Most of the animals that migrate during winter find their way back with the help of the sun, moon, and stars in the sky. They possess the skills that lead them to their original place. Such wonderful and extraordinary is the creation of nature that not a single living or non-living creature is left without food. Everyone is gifted with natural intelligence to get food and shelter for themselves. As far as the non-migratory creatures are concerned, they adapt to the climatic changes and survive the season by changing their habitats. They are capable of adjusting their food and lifestyle according to the changing conditions. Either they change their food or find a new shelter like snakes and other reptiles buried deep down in the soil to find a warmer temperature.
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FAQs on Migration in Mammals
1. What are the main reasons mammals migrate?
Mammals primarily migrate for a few key reasons. The most common triggers are seasonal changes in climate, the search for food and water, and the need to find safe places for breeding and raising young. Migration allows them to escape harsh conditions and exploit resources that are only available at certain times of the year.
2. What are some famous examples of mammal migration?
Some of the most spectacular examples of mammal migration include:
- The Great Wildebeest Migration in the Serengeti, where over a million wildebeest, zebras, and gazelles travel in a circular route through Tanzania and Kenya.
- The migration of Caribou (Reindeer) in North America and Eurasia, which undertake long journeys between their summer and winter grounds.
- The annual journey of Gray Whales from their feeding grounds in the Arctic to their breeding lagoons in Mexico.
3. How do mammals navigate accurately during their long migration journeys?
Scientists believe mammals use a combination of methods to find their way. Many use the Earth's magnetic field as an internal compass. Others navigate using the position of the sun and stars. They also rely on their memory of physical landmarks like rivers and mountain ranges, and may even use their sense of smell to follow familiar scents.
4. What is the difference between migration and simple movement like dispersal?
The key difference lies in the pattern of movement. Migration is a predictable, two-way journey that happens seasonally between two specific locations. In contrast, dispersal is typically a one-way movement where an animal moves away from its birthplace to find a new territory, and it does not return.
5. Which mammal is known for the longest migration journey?
The Gray Whale holds the record for the longest migration of any mammal. These massive marine animals travel up to 20,000 kilometres round-trip each year, moving between their cold-water feeding grounds in the Arctic and their warm-water breeding lagoons off the coast of Mexico.
6. Why is migration considered a risky strategy for survival?
While migration offers huge benefits, it is also filled with dangers. Migrating mammals face threats from predators who wait along the route, the risk of starvation or exhaustion from the long journey, and challenges from crossing difficult physical barriers like rivers, deserts, or human-made obstacles like highways.
7. How does climate change impact the migration patterns of mammals?
Climate change can seriously disrupt migration. It can change the timing of seasons, causing a mismatch between when animals arrive and when their food is available. Warmer temperatures might also make some traditional habitats unsuitable, forcing mammals to alter their ancient routes or timing, which can have negative consequences for their survival.
