Grizzlies show similar variation. In fact, the bears of Glacier appear significantly more carnivorous and predatory than those of Yellowstone. Two important food sources for grizzlies in the High Rockies are white pine nuts and codling moths. White pine nuts are important to grizzlies because they are so rich in fat and protein, and they get the bears in condition for winter. Authorities are worried that these trees are under increasing attack by pests and disease. The codling moths are a recent discovery. The moths gather in large numbers at the height of summer in rocky slopes above the tree line. The grizzlies rummage through the rocks and slurp down these moths by the ton. Grizzlies also eat a LOT of grass, especially in the spring when it is new and green and not yet high in indigestible celluose. It makes a strange impression to see these huge toothy critters grazing like so many cows. Along the north Pacific coast, from British Columbia to southern Alaska on some of the offshore islands, the primary food source are the salmon runs. It is a rich food source indeed, and these bears get bigger than any other brown bears. In northern inland areas, predation becomes more important. These bears are smaller but meaner than the big brownies of the coast. All grizzlies just love ground squirrels, above all the big groundhogs or marmots. A grizzly will think nothing of digging out two tons of dirt and gravel and moving sizeable boulders to get one of these toothsome furry morsels. Grizzlies are as well-designed for digging as black bears are for climbing trees.
A bear's diet changes according to the time of the year too. In the spring, when they first awaken, they look for winter-kill to scavenge. No meat is ever too rotten to bother a bear; besides, it is usually dripping with delicious maggots when it gets really high. Especially in tough northern climates, the bears will look for weakened, sickly hoofed animals or their new-born young to prey upon. When spring is a little more advanced, green leafy herbs (technically called "forbs") are the main item of diet. The bears eat these industriously, but they don't have a lot of calories so the bears tend to slowly lose weight. Still, it helps to get them in shape for the rigors of mating season in the late spring. During the height of mating season, the bears have less appetite. This is one of the poorest seasons for quality foods, and it is a good time for the bears to concentrate on their other biological urges. After the great mating wars are over in early summer, insects become more plentiful and the early berries show up. The bears settle down for a routine of serious munching to gain back the weight they lost in the spring. In the Rockies, bears take advantage of the seasonal effect of altitude. They start eating forbs low on the mountain and follow the belt of spring greening until they are high up. About this time, the berries are starting to ripen at the low elevations, so they go back down and follow the zone of berry-ripening up the mountain.
