Global Warming: Bad News for Gnus

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Arthur Morris / Corbis

The annual wildebeest migration is one of nature's most spectacular photo-ops. More than a million wildebeest — also known as gnus — crossing from the Serengeti in Tanzania to Kenya's Masai Mara National Reserve and then back again in the search of fresh grass makes for some dramatic action shots, as massive herds travel across the plains before plunging into the Mara River to swim to greener pastures.

The photos from this year's migration are just as dramatic, but for a different reason. This time, piles of wildebeest carcasses line the riverbanks, after 10,000 of the animals drowned trying to cross the Mara at the start of their journey back east to the Serengeti. The deaths are natural: each year, crocodiles and the strong current claim some victims. The numbers, though, are bizarre. The migration rarely leaves more than a few thousand dead; but this year, an estimated 10,000, or about 1% of the wildebeest population, were wiped out. Conservationists say the wildebeest simply chose the wrong point to cross the river, one where the bank on the other side was too steep to climb. As those in the front drowned, they trapped those behind them.

Nature can be cruel, but sometimes it gets some help. The Mara River was especially high this year, after the heavy rains that flooded parts of Africa, killing hundreds of people and uprooting thousands more. Climatologists are pointing to the downpours as proof that predictions that Africa will suffer the most from global warming and climate change are already coming true. The human toll is what makes all the headlines, but the consequences for Africa's wildlife is just as drastic.

"During the rainy season, we should be getting mild rain spread over a long time and the dry season should be reasonably mild, not too hot," says Taye Teferi, head of the Conservation Program at the WWF's East Africa Regional Program Office. "But climate change has accentuated the difference between the seasons, making the rainy season shorter and heavier and the dry season hotter." When animals migrate to the Masai Mara every spring, it allows the vegetation they leave behind in the Serengeti to regrow, ready for them to come back in the fall. No rain means no new vegetation to return to. The animals stay put and the land can't cope: The grass stops growing, the animals die. And if it rains too much, "the water, which should be a source of rejuvenation, instead becomes a force of destruction," says Teferi.

So while conservationists at the Masai Mara work hard to protect the wildebeest from poachers, they were helpless against the combination of bad luck and global warming. Brian Heath, head of the Mara Conservancy, which covers one-third of the reserve, told Britain's Daily Mail: "In a couple of days, tens of times more animals have died than were killed by poaching." According to a blog entry by Terilyn Lemaire, who works at the reserve, they considered blocking off the point where the wildebeest were crossing but then decided "It's nature. And who are we as humans to interfere with that?"

But some would argue humans are already interfering, if global warming is indeed brought about by human activity. And that may require more human intervention. The weather extremes on the African plains are getting so intense that it may no longer be enough for conservationists to simply protect nature. They might have to start improving on it. "The best thing that conservationists can do is to better design the protected areas," says Teferi. During a very dry dry season, that could mean having an area of backup grass that's opened to the wildlife only if they absolutely need it. Or, in a very wet wet season, creating an alternative migration route across a shallower part of the river. "That way, if one area is badly affected, animals have the opportunity to move to another area," says Teferi.

It's too early to tell how the mass drowning will affect Africa's wildebeest population as a whole. But it's safe to say that as the weather gets more erratic, these kinds of freak deaths will become more common — early last year, the Masai Mara had the opposite problem, and a drought left almost 100 hippos dead. These days, it looks like the only alternative to letting nature take its course is to change the course of nature.