By Laura Zuckerman
SALMON, Idaho, Sept 11 (Reuters) - Encounters between bears and humans are likely to increase in Yellowstone National Park this fall as a scarce supply of nuts forces hungry grizzlies to seek food closer to the U.S. park's popular tourist areas, officials warned on Wednesday.
Conservationists say that climate change has caused a decline in whitebark pines in recent years, which produce the nuts that are a food source for grizzlies and black bears. During this same time, several attacks on visitors have been recorded in the park straddling Wyoming, Montana and Idaho.
"We are expecting an increase in human-bear encounters and we are reinforcing safety messages," said park spokesman Al Nash.
Officials with the park and two national forests that border it said numerous recent sightings of bears seeking berries and other foods near roadways and popular trails prompted them to issue the advisory, which calls on outdoor enthusiasts to take precautions like carrying bear spray and hiking in groups.
Late summer into fall is a particularly common time for the encounters, as bears begin seeking out more food in a drive to pack on pounds before going into winter hibernation. Summer is the peak season for visitors with far fewer people hiking and camping in the fall.
Roughly 600 federally protected grizzly bears roam Yellowstone and its border states. Each year in the region there are about five encounters between the large, hump-shouldered bears and humans that result in injuries. Fatal attacks are rare.
In July 2010, a grizzly killed a camper and injured two others in a national forest in Montana near Yellowstone. The following year, two hikers were fatally mauled at the park in separate attacks that marked the first such deaths since 1986.
On Aug. 15, two hikers at Yellowstone were wounded by a grizzly that was warded off when a second pair of hikers used bear spray.
The same day, two biologists collecting grizzly habitat data in Idaho near the park were bitten by a charging grizzly that was ultimately driven off by the spray. (Reporting by Laura Zuckerman; Editing by Tim Gaynor, Chris Francescani and Lisa Shumaker)