The Gwitchin happily hunted their caribou in obscurity until Hurricane Katrina's devastation of the Gulf oil and gas production broke the political logjam blocking drilling in "ANWR." Now the Gwitchin are better known, because they are useful to those who want to prevent any oil drilling in what some like to call "the country's premier wildlife refuge." I suppose this "precious jewel of the circumpolar north" is the "premier wildlife refuge," if you ignore the rest of Alaska and huge portions of the western, continental US.
The thesis is that drilling in ANWR will mean drilling in the "calving grounds" of the caribou herd. This may lead to further dimunition of the already dwindling herd, taking down the entire ecosystem of the tundra. It's not really known why the herd has been dwindling, but the article does mention that "global warming" is happening in the Arctic. We're apparently supposed to infer that this is related in some way. Perhaps the dwindling herd is causing the global warming.
It's hard for us to believe that the caribou, which have survived thousands of years in a very inhospitable environment, will be unable to cope with presence of drilling/production crews and equipment. Chances are the caribou are highly motivated in the matter of reproduction, and they will find a workaround for the problem.