Unseasonably dry conditions are believed to be behind bear problems in both Grand Teton and Yosemite national parks this year, according to officials in those parks.

Between the two parks, five black bears have had to be destroyed -- two in Yosemite and three in Grand Teton.

In Grand Teton, it's been at least two decades since three bears have had to be put down in one year, according to park spokeswoman Jackie Skaggs. "It definitely appears to be the worst season for having bear conflicts that we've had," she says.

Of course, part of the problem lies with human visitors, who too often have left food out that the bruins can reach.

"No one knows why there has been such a spate this year," says Ms. Skaggs. "Some of the thoughts are that it's been a drought year and there's diminished natural foods in the way of berries and some of the vegetation that they would be focused on this year, and some of the cone crops have not been as good as they have been in past years."

As a result, bears become opportunistic, and when humans leave food out, the bears try to take advantage of it.

In Yosemite the story is much the same.

“This year, many of our acorns have already dropped, so it’s possible there are fewer natural food sources,” says spokeswoman Adrienne Freeman. Of course, she added, the park also experienced an earlier spring than normal that brought more people into the park at a time when bears were coming out of hibernation and searching for food.

“You have more people coming, and probably more bears awake and active, so you just have more time and location opportunity for incidents," says Ms. Freeman.

Grand Teton officials are trying to cope with the problem by sending more rangers out into the campgrounds and on patrol to educate visitors to the fact that they can't leave food out that bears can get. "You can't believe how many times that happens, where people put a pack down to go over and take a picture of the (Jackson) lake," says Ms. Skaggs. "The bears have been so quick to move on areas where they've gotten previous rewards."

And while those guilty of making food available to bears can be cited, rangers aren't always on the scene when that occurs.

"We get reports after the fact. It's not like rangers are there and can watch," says Ms. Skaggs. "We just find out that somebody watched a bear get food from a backpack that was left on the ground. ... It's not like we can pinpoint the right person at the right time."

So far all the problem bears in Grand Teton have been black bears, but rangers are concerned that a grizzly, bear No. 399, could soon get in trouble. The sow, the mother of triplets this year, was in the news earlier this summer when she bit a hiker near Jackson Lake Lodge a few times while defending an elk carcass she and her cubs were feeding on.

That incident was what Ms. Skaggs calls a "classic defensive maneuver." However, if food becomes even more scarce in the weeks and months ahead, a crucial time in a bear's life when it has entered "hyperphagia," a condition when it's focused on putting calories on for the winter hibernation, No. 399 could find herself in trouble

"She's habituated to people, but she's not food-conditioned," says Ms. Skaggs. "We've been concerned about her welfare and her cubs. ... She is not food-conditioned, and it is the bears that make that association and become food-conditioned that are the ones that become problems."

In Yosemite, officials have tallied 349 bear incidents this year through September 1, with related damage (mostly in the form of cars and trucks that had been broken into) amounting to $59,985. Back in 1998, for comparison, there were 1,313 incidents to the tune of more than $570,000 in damages, says Ms. Freeman.

While Grand Teton and Yosemite have had bear problems, things have been relatively quiet in both Yellowstone and Rocky Mountain national parks, according to officials there. Yellowstone officials did remove a grizzly from the park last month because she was associating campers with food, and in mid-July five backcountry campsites in Rocky Mountain were temporarily closed due to bear activity.

With a few more months left before bears head into hibernation, Ms. Skaggs won't be surprised if more of Grand Teton's bears get in trouble this fall.

"I hate to say it, but we still have a long time before things settle down," she says. "This may not be the last bear that we have to do something with."