Fewer visitors to Alaska's Denali National Park and Preserve are reporting seeing wolves, and officials say they are trying to find out why. National Park Service researchers estimate about 8,000 -- or 4 percent -- of the approximately 200,000 visitors who traveled the park road in shuttle buses this summer saw wolves, the Fairbanks (Alaska) Daily News-Miner reported Friday. That compares to viewing percentages of 12 percent in 2012, 21 percent in 2011 and 44 percent in 2010, they said. Tourists must ride buses on the 92-mile Denali Park road, the only access to the 6-million-acre park. Wolf counts in the park mirror the decline in tourists sightings, the researchers said. The 2013 spring count of 55 wolves is the second-lowest documented since counts began in 1986. Fewer wolf packs setting up dens near the road could be a factor in the reduced sightings, they said, but it's only one of several concerns. "Wolf abundance is one of those and probably a fairly important one, but there are other factors, such as where are the wolves in proximity to the road," park biologist Steve Arthur said. The decline in wolf viewing opportunities in the park is a concern "because wolf viewing is a very popular activity in the park," he said. "We're certainly concerned in the reduction of viewing opportunities and would like to understand more about what factors influence that activity."