Let them eat meat
So what foods are Yellowstone grizzly bears turning to as whitebark pine, formerly a major staple, dies off? The simple answer, made in spades at last week's Yellowstone grizzly bear subcommittee meetings, was that bears would eat more meat—largely big game and livestock. While the managers were fairly blasé in discussing how bears are making this major transition, on the ground and in real terms, grizzlies that eat more meat face more risks too.
The meeting began with an interesting and sobering session on the major threats to whitebark pine, featuring top experts in the field. Dr. Jesse Logan gave a thorough overview of the 2009 aerial assessment of whitebark pine impacts from an unprecedented climate-driven mountain pine beetle outbreak, documenting functional loss of whitebark pine in much of the Greater Yellowstone Ecosystem. This work was the result of a unique partnership between the Forest Service, Geographics, Ecoflight and NRDC. Logan summarized the dramatic crash in whitebark pine throughout the Greater Yellowstone, saying "mountain pine beetle is the clearest example of a biological response to warming climate that we have." Kelly McKloskey of Grand Teton National Park reviewed the Park Service's efforts to address the other major threat to whitebark pine: the non-native pathogen white pine blister rust. She commented "It [whitebark pine] is not going to look the same in our lifetime. We can't reverse the trends…"
So what does this mean for Yellowstone grizzly bears, which have been historically so dependent on whitebark pine seeds? According to researchers with the Interagency Grizzly Bear Study Team, bears are turning increasingly to meat as a substitute.
What does eating more meat mean from a population perspective, going forward? First, let's take a look at how females will likely be affected by eating more meat, because what happens to females matters most to maintaining a healthy population. Generally, females with cubs will exploit meat in situations that have the least chance of encountering male bears, which they fear will eat their offspring. So, females historically have taken advantage of winter-killed elk and bison, which are widely scattered across the landscape in spring/early summer—with less of a chance of running into aggressive males.
Now, with wolves in the ecosystem, there are fewer winter-killed game in the northern part of Yellowstone, because the herd sizes are down (as a result of climate, weather and predators) so there is less meat available in spring for females. This, combined with the fact that females are reluctant to put their cubs in harm's way, means that females are at a disadvantage in the company of wolves—one that will likely worsen as whitebark pine drops out of the system. Confirming this observation, at last week's meeting, Yellowstone Park's wolf research leader Doug Smith mentioned that females with cubs very rarely took advantage of wolf-killed elk and buffalo in northern Yellowstone.
Females do, and will, also pursue gut piles and big game killed by hunters, but this comes with great risk, as hunters are well armed, and conflicts often result in dead female bears. Unfortunately, dead females can't learn from experience, so females that choose to go after hunter-killed elk are often a dead-end street from a population perspective. So in sum, eating meat has advantages from a caloric perspective, but great risks for females—risks that will increase over time as whitebark pine dies off.
Second, let's look at the cost of eating meat to male bears. What we have seen is that males die at higher numbers if they eat more meat—meat they need in the absence of whitebark pine. Last year, for example, there were twice the number of male bears killed as were allowed under FWS standards. To support this conclusion, last year we saw livestock depredations and grizzly bear conflicts in Wyoming outside Yellowstone Park increase to unprecedented heights: most involved male bears. Agencies attributed this pattern, in part, to the loss of whitebark pine in the core of the ecosystem. In the fall, as whitebark has been declining, we've also been seeing more grizzly/hunter conflicts each year, as male grizzlies seek out gut piles, and sometimes even contest the ownership of hunter-killed elk. Many of the dead bears were male. So as with females, males will likely suffer from eating more meat, especially livestock and fall hunter-killed elk.
The record number of dead bears last year in Yellowstone, an estimated 79 total (or 13% of the population), can be explained, in part, by bears substituting native foods for whitebark pine that lead to more conflicts and deaths.
What can we say about the long-term results of this trend, and what can we do about it? While we don't know for sure, one thing is for certain, though: the population will drop if we see continued high conflict and mortality years such as 2010. The simple slogan that we heard last week "bears will just turn to meat", fails to deal with the complexity of the current situation, and the challenges of maintaining a grizzly bear population that is facing radical changes in available foods—changes that are putting bears and people into closer proximity for more months each year. Changes too that are likely to hurt the most of the most important components of the population: females.
While there are laudable Interagency and non-governmental organization efforts to reduce human-bear conflicts, such as around Cody, Wyoming and Island Park, Idaho, the 64 million dollar question is: are they comprehensive enough and effective enough to reduce conflicts ecosystem wide and prevent a population decline? And, are communities around Yellowstone ready and prepared to deal with grizzlies that are increasingly seeking foods on the periphery of the ecosystem, now that whitebark pine has functionally disappeared from Yellowstone's core? Only time will tell…
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