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Why Do Animals Migrate?

From the smallest butterfly to giant marine mammals, each species has its own migration story to tell. Why do animals migrate hundreds or even thousands of miles?

Every year millions of animals across thousands of species travel enormous distances searching for breeding grounds, a plentiful supply of food, or warmer weather. However, forced migrations due to drought, flooding, volcanic activity, earthquake, and hurricanes also occur.

To find out more about the reasons for migration and how it helps the animals please read on.

Have you ever wondered why animals dont stay where they migrate to?  Find out why here

What Is Migration?

When referring to animals, migration is defined as:

The process of animals travelling to a different place, usually when the season changes.

Thousands of animal species migrate every year, either from a breeding area to a wintering area or between foraging ranges. Migration occurs when the seasons change, with most animals migrating to warmer climates during winter and returning to their native ranges at the beginning of spring.

Migration is a behavioral adaptation to changes in an animal’s habitat and is necessary for survival, not just of the individual animal but also for the species. Animals that do not migrate will either slow down or hibernate during winter.

Some species will migrate a small distance between bordering states, while other species will travel hundreds of miles along migratory routes, many returning to the same place each year. There is much debate around how migratory animals find their way, with some experts believing that landmarks are key. In contrast, others suggest animals may use the magnetic fields around the Earth to navigate.

Many mammals hibernate during winter.  Find out more in this article I wrote

How Is Migration Beneficial?

Animals migrate for several reasons, each in a way that ensures the success of the species. The benefits of migration outweigh the enormous physical toll it takes on the animals during migratory journeys.

Food

Of all the reasons an animal may need to migrate, food is one of the most important. During winter months, especially if their native territory experiences cold, snowy weather, animals may suffer a sudden decrease in their normal food sources’ availability.

To survive, animals will begin to move to areas of warmer weather where food is plentiful. They tend to stay here for several months before making the journey home to arrive at the beginning of springtime.

Although ruby-throated hummingbirds are tiny birds that drink nectar, they are actually insectivores. They require nectar as an energy source for their incredible flying abilities, but their diet is formed entirely of flying insects.

During the winter months, insect numbers fall, so the hummingbirds migrate south into Central America’s tropics. This astonishing journey is a non-stop 500-mile flight across the Gulf of Mexico, taking roughly 20 hours to complete.

In the warm and humid climate of Mexico and Panama, insects are found in abundance, so hummingbirds will remain there until late February when they will fly home to North America. Without migration, the hummingbirds would likely starve.

Canada geese migrate for a similar reason. These giant birds require open areas of unfrozen water to dive for food and evade land predators. During Canada’s cold winter months, most bodies of water freeze over, leaving the geese with no viable food sources.

Migrating geese are a common sighting, with the recognizable V formation seen every year in September and October. Most Canada geese migrate from Canada to mid and southern states such as California and Florida where the winters are mild. Some geese that live near urban areas never migrate, as they have access to man-made water bodies that may be heated such as golf courses or ponds. As long as there is food available and a body of unfrozen water, they may not feel the need to leave.

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Breeding

While food is a vital aspect of life, so too is breeding, and conditions need to be perfect for the young to survive. Many species do not live in environments suitable for rearing offspring, so adults will migrate to a breeding range to breed and give birth.

The humpback whale is a prime example of this. Their native ranges are Alaska and Newfoundland’s cooler waters, but these are not great conditions for whale calves. Adults will migrate in large pods along the warm waters of North America’s gulf coast to their breeding grounds around Hawai’i and Mexico.

These waters are much warmer, and there are plentiful food sources for both the mothers and calves. The females need to feed to produce enough milk for their young, but as they mature, the calves will need a food source to wean on to before they begin their journey back north to Canada.

Want to know more about whales migrating? Find out more in this article I wrote

The pronghorn may appear to be ordinary antelope, but they are in fact the second fastest land mammal on Earth. Only cheetahs are faster. Pronghorns travel from Wyoming and nearby areas at the end of October before the snow falls. Their migration takes them to their breeding grounds in the warmer Southern states like California.

There is plentiful food here for pregnant females to gain weight to support their pregnancy and prepare for their calves’ birth. The herd will then begin the migration back north, timing their arrival with the start of spring, which is the perfect time for the mothers to give birth.

Not all Pronghorn herds migrate as the weather in their environment remains mild during winter. Some herds do not make it to their breeding ranges due to obstructions such as busy roads or fencing around farmland.

Sandhill cranes migrate from Texas and New Mexico on their long journey to reach breeding grounds in Canada and Alaska. Some fly as far as Siberia. As many as 650,000 cranes will pass along the Central Flyway en route to Canada.

Sandhills will stop in Nebraska’s Platte River valley, where there are lots of roosting sites, food resources, and courting ranges. The first cranes arrive at the river in late February, and the last will pass through in April.

The cranes feed on leftover grain from nearby crop fields and find other food sources around the wetland meadows. During their time along the Platte River, sandhill cranes will gain almost 10% of their body weight.

They also use these wetland areas for courting displays. They perform elaborate dances to attract their mates, and some sandhill crane populations remain in this area to raise their young.

Do you know why animals hibernate?  Find out here

Forced Migration

While most animals migrate every year to greener pastures in search of food or their annual breeding grounds, a small number of species are forced to migrate when they normally would not. Others have no choice but to find new migration routes or new areas to migrate to.

The main reasons for forced migration are:

  • Drought
  • Flooding
  • Volcanic activity
  • Earthquake
  • Hurricane

Mother nature can be unpredictable and extreme weather is often the main cause of forced migration for North America’s native species. Long periods of drought can cause temporary migration due to shortages of food and water, but animals tend to return to their home range within a year or two.

Flooding is another cause, but this can have longer-term impacts, and in the last few decades, flooding has become a yearly occurrence in many states. This means animals that never used to migrate now have no choice.

Volcanic activity and earthquakes may be less frequent than flooding and droughts, but they cause far worse damage, and the effects remain for many years. There has not been any volcanic eruption or earthquakes severe enough to alter species migration for the last few hundred years. Still, there have been instances where eruptions have forced birds to alter their migration routes.

Some species had to find new areas to forage after volcanic eruptions destroyed their migration ranges and left the environment a barren wasteland. Volcanic activity from centuries ago actually encourages migration. Every year, Yellowstone park elk herds migrate up to higher ground in search of more abundant vegetation, but a 2019 study found that migration did not have a fixed time.

The elk herds began their migration one year in early May, but the following year, most females did not leave until mid-July. This was due to their still being plenty of vegetation available for grazing, so they did not need to leave. Volcanic ash is high in nutrients and after a large eruption, the ash can fertilise large areas of grassland providing food for thousands of animals.

A small number of species may find that their forced migration is actually beneficial, and after a few generations, this becomes an adapted behavior. On the other hand, most animals forced to migrate will eventually return to their original lifestyles and home ranges once available.

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References

Dictionary, C. (2020). The Cambridge English Dictionary. Cambridge, UK: Cambridge University Press.

Hobson, K. A., Barnett-Johnson, R., & Cerling, T. (2009). Using Isoscapes To Track Animal Migration. Isoscapes, 273-298.

Milner-Gulland, E., Fryxell, J. M., & Sinclair, A. R. (2011). Animal Migration: A Synthesis. Oxford: Oxford University Press.

US Harbors. (2018, October 3). Top 5 North American Migratory Animals . Retrieved from US Harbors Coastal News: https://www.usharbors.com/2018/10/top-5-north-american-migratory-animals/

Wesley, D. (2020, February 17). Animal Migration: Why Do Animals Migrate? Retrieved from Woodland Trust: https://www.woodlandtrust.org.uk/blog/2020/02/animal-migration/

Wilcove, D. S., & Wikelski, M. (2008, July 29). Going, Going, Gone: Is Animal Migration Disappearing. Retrieved from PLoS Biology: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.0060188

Young People’s Trust For The Environment. (2014, September 12). Migration: Why Do Animals Migrate? Retrieved from YPTE: https://ypte.org.uk/factsheets/migration/why-do-animals-migrate?hide_donation_prompt=1

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