Pick up any newspaper in the Greater Yellowstone area during the fall, and you might get the impression that grizzly bears are on a collision course with humanity. Their numbers are growing, and they’ve been spotted in places where they haven’t been seen for generations. At the same time, whitebark pines, the bears’ prime fall food source, have been reduced to dead, red-needled forests in many places, thanks to an exotic fungus and bark beetles that are thriving in the absence of hard winters. In one study area, nearly three-quarters of the cone-producing trees died between 2002 and 2013. With whitebark pine nuts in short supply, managers often warn the public to be alert for grizzlies driven down from the mountains in search of food.
But the U.S. Fish and Wildlife Service hopes to change that grim narrative. According to a study by the federal government’s eight-agency grizzly bear research team, lead by the U.S. Geological Survey, the rapid decline of whitebark pine since the early 2000s isn’t the dietary disaster many predicted; so far, the bears are adapting. And since those dead and dying trees are the main thing keeping Yellowstone’s bears on the endangered list, the new study will likely be used as another volley in the battle over grizzly conservation.
Citing the new research, the Interagency Grizzly Bear Committee, a group of state and federal agencies charged with aiding grizzly recovery, recommended in late December that the Fish and Wildlife Service remove Yellowstone’s bears from the endangered species list. The delisting debate is now caught between two competing scientific narratives: Either the ecosystem is collapsing out from under bears, due partly to climate change (which is no good for whitebark pine), or else grizzlies’ built-in adaptability is helping them weather yet another change to their landscape. Whichever view prevails, whether on paper or in reality, it will have serious implications for the bears’ legal status. Beyond that, though, it will affect how managers and the public view climate impacts in one of the most intact ecosystems left in the Lower 48.
Since they were first listed as threatened in 1975, grizzly bears in and around Yellowstone National Park have increased from less than 150 to as many as 740, occupying at least 14 million acres today. Fish and Wildlife first delisted grizzlies in 2007, but after environmental groups sued, a district court ruled in 2009 that the agency had failed to fully consider the impacts of whitebark pine decline. Protections were restored, and a federal appeals court upheld the decision in 2011. But Fish and Wildlife contended that bears’ diets are varied and flexible enough to weather the whitebark decline; pine nuts have always been a cyclical crop. So the interagency committee directed the Interagency Grizzly Bear Study Team to begin reviewing three decades’ worth of grizzly research from the Greater Yellowstone ecosystem, the 20-million-acre region, consisting of the national park and adjacent state, federal and private land.
The Fish and Wildlife Service plans to make a decision soon on whether to draft a new delisting rule for public review – though if the past is any indication, court battles are likely to prolong the process. A new rule must show it’s not taking a “full-speed ahead, damn-the-torpedoes approach to delisting,” as 9th Circuit Court Judge Richard Tallman scolded in 2011. “The Service must rationally explain why the uncertainty regarding the impact of whitebark pine loss on the grizzly counsels in favor of delisting now, rather than, for example, more study,” he wrote then.
With more data now in hand and on the way, the researchers have concluded that the multitude of other foods grizzlies eat can replace piles of fatty tree nuts. If grizzlies are suffering from the loss of whitebark, researchers would have expected to see them expand their individual home ranges in search for food (which is different from overall population expansion due to their increasing numbers), and wake up skinnier in the spring. But neither appears to have happened.
Yellowstone’s bears eat over 200 different foods, ranging from high-elevation army cutworm moths and starchy biscuit root to ants and elk carcasses. Compared to bears in the mountains farther north, they are already big meat-eaters, but the study showed that they’re likely compensating for pine nuts by consuming even more meat, including insects. Evidence of bears feeding on carcasses in the fall doubled from 2002 to 2011.
Still, the population has been growing more slowly, inching up at a rate that ranges from close to zero to 2.2 percent per year, compared to 4.1 to 7.6 percent from 1983 to 2001. (Though even bear population numbers are subject to scientific controversy.) But scientists say that kind of leveling off is expected in slowly reproducing large carnivores, like bears.
The bear study team believes that the population growth is flagging – and that bears are invading new areas, like livestock-rich valleys with subdivisions – because there are more bears now, not just because whitebark pines are dying. The bears started colonizing new areas in the ‘80s, before whitebark took a big hit. Scientists blame decreased cub survival for the slowing population growth, and cub deaths are associated with high bear densities, not dying whitebark. That suggests that population growth is slowing and bears are living in new areas because they are crowded, not because they are hungry.
“Some people have said we are pulling the habitat carpet out from under grizzly bears in Yellowstone (given the decline of both whitebark and cutthroat trout), but I’m not sure I agree,” says Frank van Manen of the U.S. Geological Survey, the team’s leader since 2012. Whitebark, he says, is a valuable part of a “very diverse and dynamic diet.”