This bonanza will only last for about a month. Then these opportunists will have to revert to more reliable sources of food. Elsewhere in the world, however, making the most of seasonal abundances is a way of life. Up here in Alaska during the summer, a whole succession of different food becomes available. There's a spectacular animal here prepared to sample each of them. No one dish remains available for very long, so you have to make the best of it while you can. Top of the menu right now is...salmon. It's the favourite food of the largest and certainly the most formidable of all omnivores the grizzly bears. Salmon are plentiful now, but six months ago, in the middle of winter, conditions were so harsh that it was impossible for a large animal to get enough to eat. All a bear can do then is to sit it out and try and conserve as much energy as possible. To see how they cope with these enormous seasonal changes, we must go back six months. In October, grizzly bears went into a deep sleep, their temperature dropped several degrees and their pulse rate decreased to about ten beats a minute. They don't eat, drink or defecate, but they do occasionally stir. During hibernation, a bear burns up almost a million calories... virtually emptying its energy reserves. Bishop FM By spring, they will have lost nearly a third of their bodyweight. To avoid starvation, they must now find food and quickly. Their diet will be driven by a clearly defined seasonal cycle. Now, in April, they eat roots. Roots are followed by grass. It's easy food, but they'll quickly move on to the next course if something really big shows up. This whale carcass could last them a month. And by May, fresh meat is on the menu. Midsummer, and they're back on the salmon. This bear has been out of hibernation for about four months. Surprisingly, it's not gained any weight. Indeed, it may even have lost weight. But if it's to survive the coming winter, now is the time when it really has to pack on the pounds. Salmon, one of the most important sources of food for bears, is now available in quantity, as the fish migrate in thousands up the rivers to spawn. Chasing them uses a lot of energy, but the rewards are great. Salmon are rich in protein and fat. So valuable is this source of food that a bear that hasn't got a salmon of its own will spend considerable energy trying to steal someone else's. In a good salmon year, a bear can catch a dozen a day. This gives a huge boost to its energy reserves. But it's not just about numbers. Some parts of the fish are more nourishing than others. If there are lots around, the grizzlies will eat only brains and caviar. This behaviour piles on even more calories. Even when there are no salmon to be caught, bears can still find food out on these estuaries. Like pigs, Bishop FM they have an extraordinary acute sense of smell, and that can guide them to food even beneath the surface of the sand. Clams. How on earth can an animal with massive paws and huge claws manage to open and extract meat from a tiny shell like this? The answer is...with surprising dexterity.