The annual population estimate of Yellowstone National Park's northern elk herd is down this year, with 4,174 animals, located both inside and north of the park, recorded on March 7, 2012. That's a decline of 10 percent from 4,635 reported in January 2011, which was a 24 percent decline over the previous year. Montana Department of Fish, Wildlife and Parks and National Park Service biologists listed the causes as the harsh winter of 2010-11; predation by grizzly and black bears, cougars, and wolves; and hunting.

"All the big carnivores have made a comeback," said biologist Doug Smith, who leads the Yellowstone Wolf Project. "The Greater Yellowstone Ecosystem is now arguably the most predator-rich area in North America, with a high density rate for all four species. We have the most predators Yellowstone has had in 100 years, and we did that on purpose because people wanted it and because restoring natural conditions is our mandate." Yellowstone's wolf population peaked at 171 in 2004. It is now 98. Since 2007, the number of wolves preying on the northern herd has dropped from 94 to 38.

The herd, including elk that move into south-central Montana in winter, is the most monitored of Yellowstone's seven elk herds. From 1932 to 1960, its count neared 12,000 twice (in the 1930s). Otherwise it was 5,000 to 10,000 annually. In the 1960s, it fell below 4,000 three times, then began a steady rise, hitting 18,000 in 1988 and 1994. In 1995, the year wolves were reintroduced, the herd estimate was 17,000. Near the end of the decade, it numbered 12,000, then hit 15,000 in 2000. Most of the 2000s were severe drought years, and the population fluctuated between 10,000 and 5,000, dipping below 5,000 in 2011. Historically, the herd's size can decrease or increase 10 percent to 40 percent annually, depending mainly on the severity of winter. The winter of 2010-11 is still a factor in this year's decline, as biologists usually conduct their population estimate in late December and report in January. That was true last year. But the 24 percent decline noted then didn't cover half of that hard winter.

Hunting in Montana affects herd numbers too. In 2002, to protect habitat from elk, the state raised hunting quotas for animals migrating north from the park. But since 2003 it has significantly reduced permits for cows and calves. The state has a target goal of 3,000 to 5,000 elk between Emigrant, Montana, and the park border in winter. This year, 2,734 of the 4,174 were counted there.

The herd continues to respond to a variety of influences. Current changes in cow-calf ratios may be an indication that numbers will increase.