The Fish and Wildlife Service is proposing to delist grizzlies from the protection of the Endangered Species Act in the Greater Yellowstone Ecosystem. The basic rationale for delisting is that the geographical distribution of bears has increased, particularly in areas south and east of Yellowstone Park, as well as population growth.
Photo by USFWS Mountain-Prairie
But there is a debate about whether this is enough to justify delisting, and more worrisome, is whether the bear’s continued population growth is really ensured.
At best, there may be 700 grizzlies in the entire Greater Yellowstone Ecosystem. While this may seem like a large number, consider that grizzlies are a tournament species. That is, a few large, dominant males, do the bulk of all breeding — hence reducing the overall genetic diversity in the population.
Many geneticists believe a viable population of 2500 to 5000 bears is necessary for the long-term survival of the species. This can only be accomplished if the Yellowstone bears’ numbers increase and are eventually connected to other bear populations further north as part of a larger metapopulation.
There has been increasing mortality of female grizzlies in recent years for reasons that may be related to climate change — to be discussed in a minute. But higher mortality of females is critical since they are the source of new bears in the population.
The major argument against delisting has to do with a significant decline in Yellowstone grizzly food sources.
Whitebark pine, which has nutritious seeds, and which bears, particularly female bears, relied upon, have declined significantly due to bark beetles. The increase in bark beetle mortality in whitebark pine is attributed to global warming. As temperatures continue to rise we can only imagine even greater mortality in whitebark pine populations and loss of a major food source for grizzlies.
A second loss has been cutthroat trout. Bears used to feed upon spawning trout in tributaries to Yellowstone Lake, much as coastal brown bear feed on salmon. Lake trout, which prey upon cutthroat, were introduced into Yellowstone Lake and caused a major decline in cutthroat trout populations to the point where few to no bears feed on spawning trout any longer.
A third loss is meat. In the past, elk numbers were higher, and many elk died in winter due to starvation. This provided bears, particularly females with cubs, a ready source of highly nutritious food in spring after they left their winter den.
A fourth major source of food is army cutworm moth larvae. The moths feed on alpine flowers and lay their eggs in high rock basins. With global warming, tundra habitat is expected to shrink, which may significantly reduce this food source, or alternatively, farmers may use more potent pesticides to reduce moth populations. In any event, this other pillar of grizzly food resources may decline as well.
One consequence of these changes in food resources has been greater conflicts with humans. Female bears who no longer can subsist on whitebark pine seeds are now driven to rely more on meat. But this forces them to seek out cattle or find gut piles left by hunters. Both activities put them more in harm’s way.
The continued culling of bison in Yellowstone Park also threatens grizzlies. Like elk, higher bison populations result in greater winter mortality. Winter-weakened bison or carrion resulting from winter kill are increasingly important food for bears, particularly at a time of year when other food resources are limited. Finding the carcass of a dead bison upon existing the winter den is like winning the lottery for a female with cubs. But the on-going bison slaughter is literally taking food right out of the mouth of bears, particularly, females.
Most current mortality of bears is occurring on the fringes of its occupied habitat. But these are exactly the bears we need to ensure connectivity to other grizzly populations, as well as for population expansion.
Finally given the long time to maturity, combined low birth rate of grizzlies, bears are particularly vulnerable to population declines, which might not be immediately apparent.
Given all these factors, it is disingenuous for the Fish and Wildlife Service and the state wildlife agencies in Montana and Wyoming to suggest that bears can safely be delisted. Delisting would inevitability result in greater habitat losses and destruction. It’s time for the FWS to slow down. Let’s wait another 10 or 15 years and then revisit the grizzly delisting issue. Now is not the time to jeopardize the bear’s future.