Believe It: Killing Wolves Works
Editorial
by Cat Urbigkit, Pinedale Online!
December 6, 2014
There is much ado about a paper published this week, with headlines such as "Killing wolves to protect livestock doesn't work in the long run" and "Kill this wolf and more sheep will die." (The paper is linked below.)
Even the research host university (Washington State University) reported "researchers have found that it is counter-productive to kill wolves to keep them from preying on livestock. Shooting and trapping lead to more dead sheep and cattle the following year, not fewer."
Similar headlines are repeated in the current news cycle, but it's obvious few reporters read past the press release. I did read the journal article, and attempted to examine the data upon which the paper is based – which I could not do fully since:
1) some of the data is unavailable,
2) the literature citations are incomplete,
3) the first two references I checked did not say what the paper alleged, and 4) the researchers did not specify which counties in the tri-state research area were included in its numbers for each year.
Regardless, WSU’s flawed paper seems to be an exercise in comparing variables to seek out correlations without causation. (For examples, read The Ice Cream Murders or Cracked’s piece on broken science, both linked below.)
The WSU paper is based on the assumption that breeding pairs of wolves "are responsible for most livestock depredations," yet this vital assumption was not examined as part of the research, and the literature citation used to support the statement doesn’t support the allegation. While it is known that some breeding pairs are responsible for livestock depredations, no citation indicated that they are "responsible for most livestock depredations," and that type of data for the 25-year time period and region involved in the WSU study has not been produced. Incidentally, when we’ve had wolves killing our family’s sheep, they weren’t part of Wyoming’s tally for breeding pairs.
The researchers started with the assumption that breeding pairs are the important data set, and proceeded from there, using statistical modeling over a very large scale (the tri-state region of Montana, Wyoming, and Idaho) rather than on a smaller scale, such as regions where wolf packs reside and come into conflict with livestock – areas on a scale where previous research has revealed that lethal control reduced depredations in subsequent years. It’s generally accepted that removal of carnivores causes an immediate reduction in livestock depredations for a year or two, but the cycle begins anew when carnivores once again fill the vacancies. That’s the way of non-static ecosystems.
The selection of what data was used in the WSU research paper is important, and is center to my criticism of the entire paper and its nonsensical final result. Yellowstone National Park’s wolf packs and breeding pairs are part of the WSU data set, yet these wolves only come into contact with livestock if they leave the park.
And of course the researchers used only cattle and sheep deaths that agency professionals could "confirm" as wolf kills, despite the fact that research has indicated that for every sheep or calf confirmed as killed by wolves, up to 7 are killed by wolves and are not confirmed. The researchers also did not include other livestock that were injured by wolves but not killed, or livestock kills that were determined by agency personnel to be "probable" wolf kills.
The WSU researchers only included wolves that were killed "by livestock owners or through government control methods" – not wolves killed during legal hunting and trapping seasons in the region, or other sources of mortality. This data exclusion seems odd, since the paper begins with the statement "Predator control and sport hunting are often used to reduce predator populations and livestock depredations ..." Although Yellowstone’s wolf numbers are used WSU data, the number-one cause of mortality in the park’s wolf population is instraspecific aggression (wolves killing other wolves) , but this was excluded from the study because only wolves killed by "livestock owners or through government control methods" were included in the data set.
In another odd selection of data, the WSU researchers included wolf kills that were made by agency personnel in order to reduce predation on declining wildlife populations (and where there had been no livestock depredations).
The WSU paper did not factor in the number of incidents of livestock depredation, which can be a significant. While the total number of dead livestock is important, the number of incidents is revealing as well. For instance, the number of confirmed and probable wolf depredations on sheep increased in Idaho in 2013, including one incident resulting in the death of 176 sheep in Idaho. Interagency reports indicate that a decline in losses would have occurred with the exception of this single incident. A similar incident occurred in Montana in 2009, when 120 adult rams were killed in one incident (a huge increase from the 111 sheep killed in the state the year prior).
This cherry-picking of data is concerning, and to prove that point I’ll do my own cherry-picking from the researcher’s data in a moment.
The researchers concluded, "It appears that lethal wolf control to reduce the number of livestock depredated is associated with increased, not decreased, depredations the following year, on a large scale – at least until wolf morality exceeds 25%."
Neglected is the fact that once wolves begin preying on a livestock herd, the depredations don’t magically stop – the wolves often return, until control action is taken or the livestock are removed. It may be convenient to pretend that the depredations would not increase if the wolves are not removed, but it is not realistic. Despite the variety of non-lethal measures already in use by livestock producers, wolves still manage to kill livestock, and often the only feasible way to stop the depredations is to kill the wolf or wolves responsible for the depredations. Data from Wyoming in 2012 reveal that 27% of Wyoming’s wolf packs were involved in more than three livestock depredation events, and that there are some areas where wolf depredations on livestock are chronic – areas where the expanding wolf population moves into high density populations of livestock and, in these chronic conflict areas, it’s only a matter of time before wolves are killed after the predictable livestock depredations occur. One wolf pack was responsible for 43% of Wyoming’s cattle depredations in 2012, and three packs were responsible for 70% of the sheep depredations.
Some packs that are counted as breeding pairs are not identified as breeding pairs each year, and Wyoming research revealed: "Overall, it appeared that natural factors unrelated to known mortality sources were the primary cause of non-breeding status" for the majority of packs not classified as breeding pairs. Only three packs of 11 breeding pairs from the year prior were downgraded because of mortality from confirmed livestock depredations.
The 25% number mentioned above is interesting as well – that’s the growth rate of the region’s wolf population every year. If control efforts exceed that 25%, the wolf population (and number of breeding pairs) begins to decrease – and, lo and behold, results in fewer livestock depredations, according to the WSU researchers. But that doesn’t make the headlines.
The WSU study has inspired me to do my own cherry-picking of the paper’s data. In comparing the data from the first year to the final year (1987 and 2012), what jumps out at me is that the number of sheep in the wolf-inhabited counties of each of the three states declined while the wolf population boomed. The number of sheep declined by more than 11% in Wyoming; 70% in Idaho; and 57% in Montana – during the same time period that the minimum wolf population increased by 6,150% in Montana; 1,219% in Idaho; and 4,778% in Wyoming.
It’s also worth noting that the WSU paper simply looked at numbers taken from specific data sets, and did not consider how each wolf population was managed – be it through sport harvest or agency management. It’s an important factor as well, as noted in the annual interagency report prepared for Wyoming, which notes: "During this period of wolf population growth, wolves also expanded in range and recolonized new areas. Beginning in 2006, US Fish and Wildlife Service switched to a more aggressive approach to wolf control following confirmed livestock depredation, leading to a decrease in the number of livestock losses despite an increase in the overall wolf population. Since 2000, wolves have commonly recolonized areas outside {northwestern Wyoming’s trophy wolf hunting area}, but have rarely persisted more than a year or two before being removed for confirmed livestock depredation. These persistent damage problems and subsequent control actions limited range expansion of wolves into unsuitable habitat even while under Endangered Species Act protections. The state of Wyoming developed its wolf management framework to likewise restrict wolf range expansion into these areas of unsuitable habitat and high livestock density by designating wolves as predatory animals in these areas."
The interagency report noted that in general, wolves living in areas with relatively high native ungulate densities and relatively low exposure to domestic livestock have caused fewer conflicts with livestock than wolves that recolonized areas of unsuitable habitat where large numbers of livestock grazed on private and public lands, especially those areas outside the trophy wolf hunting area.
The WSU paper concludes: "Further research is also needed to account for the limitations of our data set. The scale of our analysis was large (wolf occupied areas in each state in each year) and the scale of some other studies were small (wolf packs). Simultaneous, multiscale analysis (individual wolf packs, wolf management zones, and wolf occupied areas) may yield further insights. "Although lethal control is sometimes a necessary management tool in the nearterm, we suggest that managers also consider testing non-lethal methods of wolf control because these methods might not be associated with increased depredations in the long-term."
Non-lethal control efforts are part of everyday ranch life in the tri-state wolf range, but are not appropriate in all situations. As state and federal officials noted in the Wyoming’s 2012 wolf monitoring report, non-lethal control is often not applicable or cost-effective in many areas in Wyoming due to: 1) specific wolf packs chronically killing livestock year after year; 2) unpredictable travel patterns and movements by wolves; and
3) very large wolf home ranges that covered vast areas including very large grazing allotments. The interagency report noted, "In instances when non-lethal control methods were ineffective, wolves were killed through agency control actions in an attempt to prevent further livestock depredations."
The WSU research paper conflicts with more comprehensive studies conducted on a smaller scale (grazing allotment, wolf pack territory or management zone), causing the WSU researchers to note: "It appears that wolf control is associated with reduced depredations at the local wolf pack scale but increased depredations at the larger wolf population scale."
Those who want to jump on the bandwagon of killing wolves only results in more livestock deaths may want to reconsider. The reality is that when wolves inhabit areas used by livestock, some livestock will be killed, and some wolves will be killed in response. What really matters is that we take action to minimize the damage to all.
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