Grizzlies range in size depending upon the area in which they are found. Bears living in the coastal areas of Alaska, places like Katmai National Park, can grow to weigh around 1000 pounds where inland bears in Canada may only grow to weigh 300 pounds. Most of the difference in size has to do with the sort of food that is available. Grizzly bears are omnivores, meaning that they eat both plants and meat. Coastal bears tend to grow larger because of the availability of Salmon and other fish, which are high in protein which help the bears to grow. Inland where meat is a rare treat the grizzlies eat mainly pine nuts, berries, roots, grasses, and insects.
Grizzlies live mostly solitary lives. Mating typically begins in late May when the males go out looking for a suitable female. Since a bears primary sense is smell the male will use his nose to try and pick up scent trails that the female leaves behind. He will follow the trail until he finds the female. The two bears approach each other cautiously, a meeting like this at other times of the year might end up in a fight, and spend some time getting to know each other. If they bond they will only stay together for up to a couple of weeks then each bear will go its own way.
If the female is impregnated she will not immediately become pregnant. The fertilized egg begins to develop but then stops at the blastocyst stage. The embryo then sits in the uterus for several months until it is time for the bear to hibernate. If the bear is in good physical condition at that time then the embryo will implant itself to the uterine wall and begin to develop and in January or February the bear will awaken to give birth. If the bear is not in good health when she begins hibernate then her body will reabsorb the embryo and end the pregnancy.
The baby bears are born blind and helpless. They will spend the rest of the winter suckling milk from mom inside the den. By the time mom wakes up from her winter slumber and is ready to leave the den the cubs will have grown to weigh six to eight times what they did when they were born just a few short months before. The young bears will spend about two years with their mother. They will continue to look to here to provide them with milk to help them grow until they get to the age when they will eat more solid foods. They will also need mom to protect them. Adult grizzly bears have no natural enemies but cubs can fall prey to other predators like coyotes, wolves , and other bears. Male bears will often kill cubs, especially ones that are with a female around mating time. While the female has cubs with her she will not go into estrus and thus will not mate. So the males know that the only chance they will have to mate with a female who still has cubs is to kill the cubs. If the cubs live to be two years old then mom will chase them away when mating season arrives so that she can start the process over again. The two year old cubs will have to fend for themselves from then on. I took these photographs in Yellowstone where there they estimate the grizzly population at around 550.