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Lack of food drives human-grizzly conflicts—and human-grizzly fatalities

The views expressed are those of the author and are not necessarily those of Scientific American.


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As their traditional food supply disappears because of climate change and invasive species, Yellowstone National Park’s grizzly bears (Ursus arctos horribilis ) are increasingly seeking sustenance outside their protected home—a move which more than ever puts them in the crosshairs.

An estimated 75 Yellowstone grizzlies where killed or "removed from the wild," as the U.S. Fish and Wildlife Service phrases it when animals are expatriated from their habitat, following conflicts with humans in 2010. Approximately 600 grizzlies live in Yellowstone, so this year’s death-slash-removal rate represents as much as 12 to 13 percent of the animals inhabiting the park. This was the second-highest number of grizzly deaths since the species was listed in 1975 as "threatened" under the Endangered Species Act. The record high was in 2008 when an estimated 79 bears were killed or removed. This year, only three reported grizzly deaths resulted from natural causes.

Although some deaths were caused by hunters who confused the grizzlies for black bears, which are not a protected species, most occurred after grizzlies wandered outside the park in search of food. In 2010 this wandering caused a record number of human–bear conflicts as well as the mauling deaths of two people.

All these problems are driven by reductions in two of the grizzly’s main food sources, which have been hit hard in recent years. The first of these is the Yellowstone cutthroat trout (Oncorhynchus clarkia bouvieri ), which is being squeezed out by nonnative lake trout (Salvelinus namaycush ). The much larger lake trout not only outcompetes the cutthroats for food, they eat the cutthroats before they can reach the shallow waters where grizzlies do their fishing.

Even worse off is the whitebark pine tree (Pinus albicaulis ), which produces high-fat nuts the grizzlies depend on as a major staple. Warming temperatures from climate change have brought the mountain pine beetle (Dendroctonus ponderosae ) into Yellowstone for the first time, leaving huge areas of dead trees in their wake . Cold temperatures once kept the beetles away, but now as much as half of Yellowstone’s whitebark pine trees have been killed by the insects. According to Defenders of Wildlife , "As the whitebark pine declines grizzly bears are spending less time feeding at high elevations and more time searching for substitute food sources, often in closer proximity to people." And according to Louisa Willcox, a senior wildlife advocate at the Natural Resources Defense Council, "The best available science (mostly done by government scientists) shows unequivocally that whitebark pine directly or indirectly drives the reproductive success and survival of grizzly bears ."

In addition to the beetles, white pine blister rust (Cronartium ribicola ) from Europe is killing off many whitebark pine trees. The fungus first came to this country around 1900, and very few pine trees have resistance to it.

Grizzlies are omnivores, and some government scientists say the bears should be able to adapt to catch and eat more elk, but it costs a lot more calories to take down an elk than to eat nuts off a tree, which provide calorie-rich sustenance the bears sorely need before their hibernation period.

Grizzlies are protected in the lower 48 states and in Canada, where their combined population is estimated at 1,000 to 1,400. Another 30,000 grizzlies live in Alaska where they are not protected. Yellowstone grizzlies briefly dropped off the endangered species list in 2007, but a federal court ordered them back on in 2009. The U.S. government is currently appealing that decision.





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  1. 1. BoRon 7:33 pm 01/4/2011

    Changes in the park due to climate change are certainly more evident than hurricanes in the article "Finding the Fingerprints of Climate Change in Storm Damage."
    Even though expected change would be increased at higher latitudes, the perceived changes vary more by "author of article" than by "location of events."

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  2. 2. dodgerh8ter 8:14 pm 01/4/2011

    The last two years have been the coldest I can ever remember here in SW Wy. Colder than before the pine beetle showed up. Yet trees still die. Maybe the pine beetle is not global warming related? Maybe people can stop using global warming for the catch all excuse when science is either too hard or the answer to elusive? I believe humans are altering the environment. I.e. I believe in global warming. But I also believe the pine beetle problem won’t be solved until we can get past the "It’s global warming" mentality that is sooooooooo pervasive throughout the national park service.

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  3. 3. jtizzi 11:34 pm 01/4/2011

    Great, global warming is causing bear attacks.

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  4. 4. ntrlstscntst 10:27 am 01/6/2011

    As a lifelong naturalist and scientist, I have to wonder why articles like this, along with the subsequent "comments", are written with such obvious non-scientific, non-factual, political, and emotional inputs. Aren’t responsible editors supposed to screen material such as this? Don’t we all actually care about our planet, the environment, and its wildlife? Assuming the answer is "yes", then why do so many folks provide politicized misinformation, and obnoxiously attack those who don’t agree with them, and/or those who do/don’t understand the actual facts and science behind the issues?
    (Submitting in multiple parts, due to character limitations)

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  5. 5. ntrlstscntst 10:28 am 01/6/2011

    To quote sources such as "Defenders of Wildlife" and "Natural Resources Defense Council" as trustworthy sources of reliable, scientific, intelligent, non-politicized information is completely disingenuous and ludicrous. Yet, the misguided "anthropogenic global warming" folks thrive on this sort of misinformation and non-scientific approach to furthering their pseudo-environmentalist and political purposes. Why not stick to the FACTS, actual scientific data,and logical methods? If they were truly environmentalists who want to help the environment, animals, ecosystems, etc. as much as possible, they would want to embrace the most rigorous scientific methods available, generating actual factual information and theories (yes, "theories" are okay in the absence of supporting data), instead of the manipulative garbage they’re usually embracing as fact and truth.

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  6. 6. ntrlstscntst 10:29 am 01/6/2011

    It’s probably true that the 600 grizzlies living in the Yellowstone area are getting a bit crowded, and the more bears there are, the higher the chances are for human-bear encounters. To avoid this, as well as to find more food, some of the bears probably try to move to less crowded surroundings, thereby increasing their exposure to even more humans. This is a natural situation that has to be dealt with through effective wildlife management by qualified wildlife biologists, not by unqualified "environmentalists". Now that humans are here, there’s no going back to the days when humans had no influence on the wildlife, so "environmentalists" should accept this fact. The overall natural environment, and all its associated ecosystems, has been irrevocably changed, and there’s no going back; fixing little pieces of it is difficult, when all the interactions cannot be anticipated. Just look at the wolf reintroduction fiasco!

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  7. 7. ntrlstscntst 10:30 am 01/6/2011

    I actually live in an area where the native pine forests have been devastated by "pine beetles" of various species, and I’ve studied the causes and effects for many years. Whereas global temperatures are very slightly higher now than they were some decades/centuries ago, there has been absolutely NO scientific data or proof indicating this has any affect on the beetles and the trees they’ve killed. So presenting this as fact is inaccurate and dishonest. Instead, the beetles have natural population cycles, and we’ve been in one of the high population cycles for the past 4-9 years, depending on geographic area. The REAL scientists studying this phenomenon do NOT attribute it to global warming, but instead relate it to the Rocky Mountain west returning to normal dry conditions (not caused by humans), which results in stress on the pines, weakening their defenses and allowing beetles to kill the trees. If someone is looking for a human-effect in all this, it probably comes in the form of a century of forest-fire suppression in areas that actually benefit from the fires; natural forest-fires help to buffer beetle populations and reduce widespread beetle damage. So the bottom line is that the reduction in the grizzlies’ food source (pine nuts) is real, but the cause is NOT global warming.

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  8. 8. ntrlstscntst 10:30 am 01/6/2011

    Next, humans (criminals) certainly did introduce non-native lake trout into the Yellowstone area lakes. Therefore, this proposed loss of grizzly food (cutthroat trout) is completely human-induced. I know wildlife biologists are working to remedy this problem, but it’s a difficult battle to eliminate one trout species out of the lakes while leaving the other intact. The only way to be completely effective in this effort is probably to capture/save 1000s of the cutthroats in a hatchery, sterilize the lake, and reintroduce the cutthroats. But is this the right thing to do, for the right reasons?

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  9. 9. ntrlstscntst 10:31 am 01/6/2011

    Since we’re talking about bear food, we also need to talk about the terrible situation with the wolves in the Yellowstone area. Environmentalist groups ignorantly pressured and supported the reintroduction of wolves into Yellowstone, and continue to do so. Unfortunately, these groups, their political machines, and some of the brain-washed biologists out there forced the reintroduction, against the recommendations of many wildlife biologists (who were the wise ones). The wolves have now vastly over-populated the area, and there are now in excess of 10 times as many wolves as the original plan accounted for; this was caused by the highly prolific wolves being placed in an environment with an unlimited food supply and basically no competition. This potential problem was foreseen by some, but was ignored by those allowing their emotions, ignorance, and politics to rule their actions, and we’re now faced with an unmitigated disaster for the Yellowstone ecosystem. What’s the affect of all this on the grizzlies? The 1000s of wolves have killed >70% of the elk in the Yellowstone area, as well as nearly all the moose. So there goes another of the grizzlies’ food supplies, which is easily as significant a loss to the bears as either the pine nuts or the trout. So why didn’t the author or the "environmentalists" mention this situation? Maybe because it was anti-wolf? Hmmmm….

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  10. 10. ntrlstscntst 10:32 am 01/6/2011

    Since we’re talking about bear food, we also need to talk about the terrible situation with the wolves in the Yellowstone area. Environmentalist groups ignorantly pressured and supported the reintroduction of wolves into Yellowstone, and continue to do so. Unfortunately, these groups, their political machines, and some of the brain-washed biologists out there forced the reintroduction, against the recommendations of many wildlife biologists (who were the wise ones). The wolves have now vastly over-populated the area, and there are now in excess of 10 times as many wolves as the original plan accounted for; this was caused by the highly prolific wolves being placed in an environment with an unlimited food supply and basically no competition. This potential problem was foreseen by some, but was ignored by those allowing their emotions, ignorance, and politics to rule their actions, and we’re now faced with an unmitigated disaster for the Yellowstone ecosystem. What’s the affect of all this on the grizzlies? The 1000s of wolves have killed >70% of the elk in the Yellowstone area, as well as nearly all the moose. So there goes another of the grizzlies’ food supplies, which is easily as significant a loss to the bears as either the pine nuts or the trout. So why didn’t the author or the "environmentalists" mention this situation? Maybe because it was anti-wolf? Hmmmm….

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  11. 11. leif@colo-earthfriends.org 7:59 pm 01/6/2011

    I ended my subscription to SA in 2007, after Kevin Trenberth’s idiotic article about the inevitable increase of stronger and more hurricanes as a result of "global warming." Recent tropical storm activity, documented at Maue’s Florida State U website, either confirms that Trenberth is right and that global cooling is taking place OR that Trenberth is wrong and global warming/cooling has no effect on hurricane number/intensity.
    This article doesn’t encourage me to come back. "Global warming" is not the be-all and end-all of environmental science. A specialization in radiative transfer theory makes me very skeptical of the CO2 "greenhouse gas" hypothesis.

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