Two more bears have been lost in the greater Yellowstone ecosystem, one to an apparent car collision and another to undetermined causes, according to Yellowstone National Park officials.

On Wednesday park officials reported that a large boar grizzly was found dead a bit north of Fishing Bridge in the park's interior, and that a young black bear was found south of Fishing Bridge, an apparent victim of a hit-and-run driver.

The grizzly, weighing nearly 600 pounds, was found Tuesday about 50 yards off the road and one-half mile south of LeHardy Rapids, north of Fishing Bridge, the park reported. The bear, medium brown in color, weighed 576 ½ pounds. Its carcass was being sent to Bozeman, Montana, for a necropsy to determine cause of death.

Meanwhile, the body of a young male black bear, weighing 79 pounds, was discovered in a ditch next to the road south of Fishing Bridge, about halfway between Lake and West Thumb, park officials reported, adding that it's believed the bear was hit by a car or truck sometime Tuesday afteroon.

Yellowstone officials say a total of four black bears have been killed inside Yellowstone this year; two in motor vehicle accidents and two problem bears that were euthanized. Three grizzly bears have been killed in the park this year; one by a motor vehicle, one in a trapping accident, and the most recent whose cause of death is still unknown.

A search for food might be driving the bears into the park's lower elevations, and into conflicts with human visitors. The Interagency Grizzly Bear Study Team this week reported that production of whitebark pine cones is low this year, Yellowstone officials said. The seeds from these cones are a favorite fall food of grizzly bears. When these seeds aren’t available, grizzlies tend to eat more meat and roots, they added.

Park regulations require people to stay 100 yards from black and grizzly bears at all times. The best defense is to stay a safe distance from bears and use your binoculars, telescope, or telephoto lens to get a closer look.

Yellowstone visitors are reminded to keep food, garbage, barbecue grills and other attractants stored in hard-sided vehicles or bear-proof food storage boxes. This helps keep bears from becoming conditioned to human foods, and helps keep park visitors and their property safe.

Hikers and backpackers are being encouraged to travel in groups of three or more, make noise on the trail, and keep an eye out for bears. Bear pepper spray has proven to be a good last line of defense if you keep it handy and use it according to directions when the bear is within 30 to 40 feet.