Every summer, the Serengeti plains (平原) of Africa are worthvisiting. Millions of wild animals begin their 1,800-mile journey northwards ontheir migratory (迁移的) route every year.

In the month of November, polar bears intheir thousands cross the Canadian Arctic, as they head towards the ice sheets ofHudson Bay. The sea ice that forms every winter is the key to the bear's managingto be alive, for here they hunt for seals (海豹).

The Great Bustard, one of the heaviest flyingbirds, migrates each year across Europe and Asia to its wintering grounds. Unluckily,these and other migratory animals are in danger from human activity.

We have written several articles on climatechange and the influence of rising ocean temperatures. Since 1979, ice sheets inthe Arctic have gone down by 30 percent. What does this mean for polar bears? Theyare forced to stay on land for longer periods of time, which delays their searchfor food. As a result, bears today are 60 pounds lighter than what they were. Besides,smaller bears also produce weaker babies, and their chances of survival are at risk.In the plains of Africa, migratory animals like gazelles are traveling long distancesfor food, just to avoid falling prey (牺牲品) to humans who hunt them.

In an unusual step, experts from 120 countrieshave agreed to protect 31 migratory mammals, fish and birds. The United Nation's11th annual Conservation of Migratory Species of Wild Animals (CMS) was held inQuito, Ecuador. For the first time, 900 experts attended the conference, and theenthusiastic support shows the world is united in conservation (保护) efforts.

What does getting on a protected list mean?Countries that have signed the agreement will be required to pass laws locally andwork with other countries that fall within the animal's migratory path. Only oneanimal did not make the list. The African lion was rejected (拒绝) for lack of informationof the countries where it lives.