Every year before Spring Festival, Chinese people begin the "Spring Festival travel rush" which lasts for 40 days. During this period, people who work in other cities, provinces or abroad set off to their hometowns and reunite with families. For 2020, it is estimated that three billion trips could be made during Spring Festival travel rush. The massive travel rush is jokingly called "the biggest mammal migration on the earth" by netizens. 

Animals in the wild have "travel rush," too. Though they do not have trains or flights, they migrate across amazingly long distances in massive scale. Despite that animals do not bring money and gifts home, they also travel with a mission in mind. 

The Great Wildebeest Migration across Northern Tanzania and Kenya is a truly spectacular event. Over two million wildebeest, zebras and gazelles move through the Serengeti and Masai Mara ecosystems. This is surely one of the greatest wonders of the natural world. 

Wildebeests migrate for a simple reason: water. Water means green pasture, and the wildebeests travel more than 2,800 kilometers every year for that. You may see the Great Migration in Tanzania all year round – they migrate in a circular, clockwise motion around the Serengeti National Park.

It is an extremely dangerous journey. Predators including lions, leopards, cheetahs and crocodiles take the migration as a good opportunity to feast. But for the wildebeests, they have no other choice, sometimes you have to risk death in order to live. 

Among all known animal migration, arctic terns are the champions of long distance – the birds fly between the Arctic and the Antarctic every year. The average annual migration distance of arctic terns is 70,900 kilometers, and the longest can be 81,600 kilometers. In an arctic tern's life (the birds can live more than 30 years), the total distance it flies across can cover three earth-moon round trips. 

The long flight is well rewarded. Arctic terns enjoy the most sunlight as they stay in the northern hemisphere for summer, then fly to the southern hemisphere for summer there. When the arctic is shrouded in the darkness of polar night, the arctic terns are staying in the Antarctic, feasting on krill. As spring begins in the north, they fly back for breeding. 

Like other salmon species, the Chinook salmons only breed once in their lifetime. And they must return to the spot where they were born for breeding. Every year, the salmon school migrate from Bering sea to the origin of Yukon river, a total distance of over 3,000 kilometers. This is the longest migration in freshwater. 

During the epic migration, the Chinook salmons barely eat. When they get back to where they were born, the females begin to lay eggs, and males fertilize them. Most salmons die after breeding. 

The monarch butterfly is the only insect that migrate periodically between south and north. For birds and other animals, the migration is an annual activity; but for the monarch butterflies, they can only complete part of the migration in their lifetime. It takes three to four generations to complete one travel. 

Monarch butterflies breed in February and March in California and Mexico. The newborn butterflies fly north to the northern America and Canada, but their lifespan is no more than eight weeks, which is not enough to cover the whole journey. The butterflies breed on the way and die; new generations keep going. In August and following months, the monarch butterflies reach the north and stop breeding as they start to fly back. 

Finally, the monarch butterflies will get back to where their ancestors were born, and stay there for winter. The Mexican residents believe the butterflies are the souls of their passed family members, so the monarch butterflies will be warmly welcomed when they return. A new journey will begin in the next spring. 

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