The science of wolves

“What can be asserted without evidence can also be dismissed without evidence.” -Christopher Hitchens

From 1865 to 1957, Wisconsin held a bounty on gray wolves and during that time the statewide wolf population declined from 3,000 (a conservative estimate) to zero. The bounty was a reflection of deep seated negativity towards the wolf (“The only good wolf is a dead wolf”) and, sadly, was effective in its goal of eliminating the animal from Wisconsin.

A lot has changed since then. In 1967, gray wolves received the protection of the federal Endangered Species Act. By the 1970’s, wolves from northern Minnesota began working their way back into Wisconsin (wolves were NOT reintroduced in Wisconsin) and the population has since worked its way back to around 800 wolves. Wisconsin’s wolf population created a bridge for the re-colonization of the Upper Peninsula which now numbers more than 200. Wolves have been here in Dunn County for several years.

Throughout its history, the wolf’s destiny has often been in the hands of human beings. We have collectively made decisions that have both harmed and helped the animal; decisions that were shaped by widely-held beliefs and perceptions that were not always based on facts or logic. Whatever your personal opinions are about this animal, they should at least be grounded in facts and logic. Or else, as Christopher Hitchens reminds us, your opinions can be easily discarded.

So, I’ve decided to compile a scattershot of evidence and resources that might add new dimensions to the way that you think about the role of gray wolves on Wisconsin’s landscape. I’ve tried to select items that portray the complexity of this many-faceted issue. My hope is that readers on both sides of this issue are open-minded about the evidence.

Wolves chasing a moose on Isle Royale National Park.

Caroline Fraser, a journalist who writes about ecology, nicely summarizes some of the science surrounding “trophic cascades” (something that causes a big shift within a food web) as they relate to predators. This is the line of evidence that shows relationships between the presence of wolves, the regeneration of willow due to decreases in elk density followed by a range of other indirect effects. Specifically, she addresses the research in Yellowstone National Park.

In 1995, the terrestrial camp landed an extraordinary boon as Yellowstone National Park gave William Ripple, director of Oregon State University’sTrophic Cascades Program, the chance to study top-down forcing in action. Ripple watched in amazement as the wolf’s return to Yellowstone — an ecosystem where elk had had the browse of the place for 75 years — gave willow and other trees the chance to take hold along stream banks, cooling water temperatures for trout and encouraging the return of beaver, whose ponds host long-absent amphibians and songbirds. Yellowstone proved that damage to a terrestrial food web could be reversed and an ecosystem restored with the return of a single species. It is a sobering lesson for the eastern U.S., where the explosion of white-tailed deer has eradicated hemlock, a keystone species in once-biodiverse hardwood forests.

While we’re on the subject of trophic cascades, Tom Rooney and Don Waller have investigated the impacts of deer on the composition of plant communities Wisconsin’s forests.  They have observed changes in tree regeneration, species abundance, vegetation structure, and nutrient cycling. Of course, deer populations are function of many factors — winter mortality, disease, habitat — of which wolves are only a single element. But, nonetheless, wolves may play a role in regulating some of the impacts to plant diversity observed by these researchers.

Ungulates can profoundly alter the structure and composition of forest communities via both direct and indirect mechanisms.  Individual plant species often respond in a unique way to the direct effect of herbivory as a function of their sensitivity to browse damage, ungulate food preferences, and the density of ungulates present. Sustained browsing pressure can limit the regeneration of favored and susceptible woody plants and eliminate populations of favored or susceptible herbaceous plants. These losses, in turn, give rise to indirect effects via trophic cascades or physical habitat modification. These indirect effects affect many other plant and animal populations. In the mixed conifer–hardwood forests around the Great Lakes in North America, widespread habitat modification and the extirpation of native predators and other ungulates have acted to boost populations of white-tailed deer (Odocoileus virginianus) to historically high densities. Such densities have curtailed regeneration of several important conifers (e.g. Tsuga canadensis and Thuja occidentalis) as evidenced by demographic analysis. Deer also appear to limit regeneration of Quercus and Betula in many areas. Impacts on understory herbs are harder to assess, but baseline data from 50 years ago indicate that these communities are changing in a pattern that implicates deer: grasses, sedges, and some ferns are increasing while overall herb diversity is declining. Thus, deer are playing a keystone role in these communities.

Are the impact of wolves on the deer herd exaggerated? This Minnesota DNR article summarizes findings from the longest run designed field experiment on white-tailed deer that was conducted for 15 years in  northeastern Minnesota’s Chippewa National Forest in which a staggering number of deer (almost 500) were radio-collared and monitored. Among other things, researchers observed the patterns in wolf predation on white-tailed deer. Through an analysis of fat-reserves in deer prey, wolves were indeed shown to take old and sick deer.

The ensuing data toppled several myths about how wolves affect deer populations. One myth held that wolves hurt deer populations by engaging in surplus-killing (taking more prey than they can eat, a behavior documented among carnivores worldwide). During the severe winter of 1995-’96, DelGiudice indeed documented incidences of surplus-killing by wolves, with some wolves taking down four deer within spans of 100 yards. But as he examined the fat reserves on the deer carcasses — and evaluated their nutritional fitness from urea nitrogen in urine samples — DelGiudice found that most of the wolf-killed deer were seriously undernourished and about to die anyway. The wolves were just finishing off deer on their deathbeds. Relatively little surplus-killing by wolves was observed during the following winter of 1996-’97, and none during any of the other 13 winters.

And what about the folks who say they’ve been hunting the same woods ever since they were kids and now they don’t see any deer during the November gun season? Wolves, right? Well, maybe not. Evidence from DelGiudice’s research suggests that wolves are actually not very efficient at taking deer. He asks hunters to consider the complexity in natural systems, that local deer populations and distributions are driven by many factors that are sometimes hard to detect from year to year.

The overwhelming preponderance of evidence based on our findings… does not support the notion that wolves move into an area and come to dominate portions of the woods in the fall (or any other season) by either preying on large numbers of the resident deer or causing them to flee clear out of that area.

Wolves are not particularly effective hunters of white-tailed deer. Despite the fact that deer outnumber wolves in Minnesota’s forest zone by some 175 : 1 (600,000 deer : 3,000 wolves), wolves must range and search widely over large pack territories (52 to 555 km² ( 20 to 214 mi² ) to obtain the number of deer (15 to 20 adult-sized deer per wolf) they require to sustain their numbers over time. Indeed, studies have shown quite clearly that most of their hunting attempts are brief and unsuccessful, typically lasting a matter of only a few minutes. And so, as has been documented for years [that] wolves live a “feast or famine” existence, eating little for up to two weeks at a time.[…]

But the wolves’ limited success in preying on healthy deer is probably more a reflection of this prey’s exquisite skills in avoiding wolf predation rather than of the inadequate predatory abilities of the wolf. White-tailed deer are highly vigilant animals, able to forage almost continuously during feeding bouts, and yet, respond very quickly to the sights, smells, and sounds of wolves and other predators. Once wolves begin hunting in a specific area, deer become increasingly vigilant, and when a wolf is detected and the decision to flee is made, a healthy deer can reach a top speed of at least 56 km per hour (34 miles per hour) and can hurdle obstacles as high as 2.4 meters (8 feet). The bare ground or shallow snow cover typically found during northern Minnesota’s early November firearm season is most favorable to the deer’s escape from wolves, and consequently, wolf predation rates on them are very low. From 1991 to 2005, a total of only 7 of 677 female deer radio-monitored during the November firearm seasons were killed by wolves; these occurred over six of the fifteen firearm seasons. No deer were killed by wolves during the other nine firearm seasons.

Radio-collared wolf

David Mech questions the validity of the research behind the “ecology of fear” hypothesis, which purports that the presence of wolves modify the foraging behavior of herbivores such as elk and, therefore, cause an indirect regeneration of willow and aspen trees and, therefore, cause an indirect increase in beaver populations. Mech points out potential flaws and concerns in the well-publicized research regarding the cascading effects of Yellowstone National Park’s wolf reintroduction. It seems to me that his primary concern is that the research is deriving too many conclusions from purely correlational data and is not properly untangling a multitude of other factors. The fact that this paper is written by David Mech, a leading wolf researcher since the late 1950′s, lends these arguments a lot of credibility.

Historically the wolf (Canis lupus) was hated and extirpated from most of the contiguous United States. The federal Endangered Species Act fostered wolf protection and reintroduction which improved the species’ image. Wolf populations reached biological recovery in the Northern Rocky Mountains and upper Midwest, and the animal has been delisted from the Endangered Species List in those areas. Numerous studies in National Parks suggest that wolves, through trophic cascades, have caused ecosystems to change in ways many people consider positive. Several studies have been conducted in Yellowstone National Park where wolf interactions with their prey, primarily elk (Cervus elaphus), are thought to have caused reduction of numbers or changes in movements and behavior. Some workers consider the latter changes to have led to a behaviorally-mediated trophic cascade. Either the elk reduction or the behavioral changes are hypothesized to have fostered growth in browse, primarily willows (Salix spp.) and aspen (Populus spp.), and that growth has resulted in increased beavers (Castor Canadensis), songbirds, and hydrologic changes. The wolf’s image thus has gained an iconic cachet. However, later research challenges several earlier studies’ findings such that earlier conclusions are now controversial, especially those related to causes of browse regrowth. In any case, any such cascading effects of wolves found in National Parks would have little relevance to most of the wolf range because of overriding anthropogenic influences there on wolves, prey, vegetation, and other parts of the food web. The wolf is neither a saint nor a sinner except to those who want to make it so.

The science of ecology is perhaps most compelling when it enters the realm of public policy. Regarding At 169, the Wisconsin statute authorizing the wolf hunt, retired DNR wolf biologist Dick Thiel testified in front of the Natural Resources Board and questioned the underlying science used (or not) by legislators. In short, Thiel points out the the population goals used to design the wolf hunt are based on an outdated management plan that fails to consider the must up to date science. He also points out that Wisconsin’s wolf experts were conspicuously absent from the legislative process that created Act 169.

Our peers in other states, other governmental agencies, and staffs in NGO’s throughout the Nation have regarded the Wisconsin DNR’s handling of wolf recovery and wolf management over the past 30 years with utmost respect. The Department has displayed great integrity in handling management of this controversial species. Sadly – with the passage of Act 169 – many of our peers are left wondering whether that track record is at risk. The Agency’s future actions rest with the guidance of the Natural Resources Board.

Act 169 is written from the perspective of individuals, parties, groups that have a single objective in mind: to drive our state’s newly recovered wolf population back in the direction of endangerment. The “authority” is based upon the DNR’s existing Wolf Management Plan. A Plan that is presently 13 years old, is based on antiquated science, and guides DNR policy despite a growing body of knowledge that has replaced much of the science the 1999 plan was based on.

And, finally, for a fascinating glimpse into the life of a wildlife ecologist, here is Michigan Tech’s John Vucetich’s “Scientists at Work” series that ran in the New York Times last year about his research team’s work on the wolf and moose populations on Isle Royale. The writing is compelling in and of itself, but it also paints an incredible portrait of the physical intensity of doing good science in the field. It lends a reminder that ecological data is not just pulled out of a hat, its the product of tough work and intimate encounters with mother nature.

The Chippewa Harbor Pack covers only a few more miles through the night. By midmorning we find the wolves traveling northeast through thick, tangled cedars in a drainage just southwest of McCargoe Cove. On at least two occasions in the past month, they tracked and chased the cow and calf that live in this area. Both times, the wolves failed. They almost certainly know half a dozen or more sites where they can find another cow and calf. There must be something about this particular pair. Maybe the mother is inexperienced or old, or maybe the calf is underdeveloped.

Even from the privileged vantage of the Flagship, it is nearly impossible to see the wolves through the dense cedars. Maybe once every third circle, we glimpse one wolf as it passes from one cedar to the next. After quite a few more circles, a moose runs out of the swamp and over an open ridge top. A moment later the wolves appear on the same ridge top, but the moose is long gone. The wolves lie down on the ridge and sleep for several hours. It is entirely possible that the Chippewa Harbor Pack has chased or tested half a dozen moose or more in the past 36 hours. It is not easy to kill an 800- or 900-pound moose with your teeth.

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