91热爆

In the remote northeast of the Yellowstone wilderness are the Beartooth Mountains. Here, surviving above 8,000 feet, a tree now welcomes the change of season: the whitebark pine. All summer these trees have been soaking up the energy of the sun, preparing for this moment. Now they offer the animals of Yellowstone a bumper crop of pine cones. The whitebark pine is gambling on the fact that animals now need all the food they can get before winter and is hoping it can entice them to spread its seeds far and wide across Yellowstone. So inside the cones it has put tasty, nutritious pine nuts. Pine squirrels snack on the nuts and bury them one by one in sheltered hollows. If they're hidden well and packed carefully they should last the squirrel through the winter, but this isn't much good for the tree: its seeds have gone nowhere. A grizzly bear mother and her four cubs are also after the pine nuts. It's unusual for a grizzly to have so many cubs, but this mother has found two orphans and adopted them. With four cubs to fatten up before they go into the den to hibernate this winter, she鈥檚 after the pine nuts because they contain 50% fat. In a good year, a grizzly bear can put on five pounds a day eating nuts alone that they dig up once the squirrels have done the hard work getting them off the trees.