Aug. 27, 2010 -- With permanent food sources becoming more and more scarce, the grizzly truth is more bears are likely to hunt for food around your campsite.
The Western Grizzly population has nearly tripled in the last 35 years in the Yellowstone National Park area, from under 200 to nearly 600. Their need for food and territory have caused them to spill out of the park's "Primary Conservation Area" (PCA).
Some wildlife authorities warn that this year with a shortage of food, specifically spawning cutthroat trout and the seeds from white bark pine trees, more hungry and potentially dangerous bears will be out scavenging.
Bear attacks have made headlines all summer, most recently when a captive bear in Ohio killed a caretaker.
In July, in Yellowstone National Park, a bear attacked three sleeping campers, killing one of them and injuring the others.
"About 2 o'clock in the morning, I felt the entire tent just fly two to three feet," said Ronald Singer, one of the bear attack victims.
"Next thing I know, this bear is chewing on my arm," said Deb Freele, another victim. "I screamed. He bit harder, I screamed harder."
Another hiker was mauled and killed by a bear in June, again near Yellowstone.
When a bear kills a human in the wild, park authorities hunt the bear and put it down because they don't want a bear running wild with a taste for human flesh.
"We won't be satisfied until we prove we have the right bear, and until we catch all the cubs," said Andrea Jones of Montana Fish, Wildlife and Parks.
Even bears who have been exposed to the lights and noise of a movie set can be deadly. Such was the case with Rocky, an enormous, well-trained bear who had appeared on several TV commercials and movies -- including one starring Will Ferrell.
In 2008, experienced animal trainer Stephen Miller was play wrestling with Rocky for a website promotion video. Suddenly, Rocky turned violent and mauled Miller, who collapsed and died in front of the camera crew within minutes of the attack.
"He was like my younger brother, you know, I raised him, he looked up to me; just dying in your arms like that, there is no greater pain," said Miller's cousin Randy Miller.
Wildlife officials considered having the bear killed, but decided in the end it was an accident. Rocky has since been restricted from working in films and television, but Miller hopes to get permission to get him back to work soon.
"I have put in my will, that if anything were ever to happen to me with one of my animals, not to blame the animal, not to put the animal down," said Miller.
Documentaries Highlighting Bear Attacks
National Geographic is running two documentaries on Grizzlies. In "Dangerous Encounters: Alaska Bear Country and Beyond," premiering Friday, Sept. 3, host Brady Barr traveled to Alaska to show how dangerous it can be to surprise a bear in the forest.
Barr strapped himself in a cage and allowed a 1,500-pound bear to try to push him over, which the animal did with ease.
Biologist Dr. Chris Servheen, who studies bear behavior, is featured in the other documentary, "Grizzly Face-to-Face," which premieres Sunday, Aug. 29. He explains some of the bears' seemingly violent behavior.
"They do a lot of play with each other as they grow up and that's how they're learning skills, just like puppies," Servheen said.
If You Encounter a Bear ... Don't Run
The National Park Service offers some tips on what you should do (and not do) if you find yourself face-to-face with a bear.
Do not run away, scream or make eye contact. Speak in soft tones and if the bear charges, stand your ground because you cannot out run it. Your best line of defense is to always have a can of pepper spray with you to spray the bear in the face if it gets too close.
ABC News' Lauren Effron contributed to this report.