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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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.
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.
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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Q1: What Triggers Migration in Mammals?
Ans: The main reasons for the migration of animals are climate change, food availability, season, or mating. Many species migrate between the two destinations at a particular period of the year. The migration is mostly annual as it involves a considerable long-distance. However, in some cases, it may be a short distance too. As we know, these species cannot adapt to the changes, so they parade to another place. The most surprising thing is the two destinations remain the same and the route too unless there are drastic changes in the atmosphere of the places.
Q2: How Do Animals Find Their Exact Migration Destination?
Ans: This is a sort of challenge to science. Only after studying a lot of animals and birds and doing many experiments, our scientists could put some light on this. Many of the migratory species use the sun as their guiding tool. With the change of the sun's position, while rotating around the earth, the animals or birds trace their path. By using the sun compass, the migratory species make 'time compensation.' Apart from that, the animals or birds that migrate during the night use the star compass similarly. They find a way with the help of North Star, Polaris.