Assessing Factors That May Predispose Minnesota
Farms To Wolf Depredation on Cattle
Discussion
The only definite and significant differences we found between farms suffering chronic losses to wolves and their nearby matching farms that experienced no losses were a suite of related size characteristics: size of farm, number of cattle, and longest distance of stock from human dwellings. Our findings regarding carcass disposal were unclear.
A number of possibilities may explain why larger farms with more cattle pastured farther from human dwellings suffered more wolf depredations. Larger operations may have had greater exposure to wolf depredations simply because of their size and perhaps because wolves were attracted to larger herds. Maximum distance that stock was pastured from human dwellings, due to the larger farm size, would not seem to be relevant because wolves often kill stock near houses and buildings. Furthermore, we know of no reason the difference between the 2.8-km mean maximum distance for chronic farms and the 1.1 (± 0.5)-km distance for the matching farms would be meaningful to wolves, and the difference between the mean distances of cattle from the houses in the 2 groups would be even less. Larger farms and herds also may have had less human presence. Conceivably, farm size itself was a neutral factor, but some unknown factor related to farm size was causative.
There are several possible explanations for the counter-intuitive and equivocal nature of the findings about carcass disposal. Eighty-five percent of chronic farms reported properly disposing of carcasses, whereas only 56% of matching farms reported proper disposal during the same survey. Conceivably, at least some farms with chronic losses, having been visited so frequently by government personnel and advised to dispose properly of carcasses, actually did so, an interpretation at least partly supported (Fritts et al. 1992).
Other possible explanations are: 1) farmers with chronic losses may be making a sincere effort to alleviate their problem by properly disposing of carcasses; 2) larger operations may have more need for systematic carcass disposal and therefore more efficient methods—for example, preparing a large pit for frequent use; or 3) larger farms may be more likely to own heavy equipment to bury carcasses.
On the other hand, false reporting about livestock carcass disposal also may have been a problem with chronic farms. This interpretation is supported by the disparity between interview results from farmers suffering chronic losses and the recollections of WS personnel. This disparity may be due to the different periods covered by the 2 types of data collection. Our survey covered only 1998, whereas the recollection of WS personnel spanned a decade or more. Perhaps some chronic farms had carcass dumps prior to 1998 but no longer have them. Potentially all these factors were operating.
Although these confounds prevent any firm conclusion, some interesting insights into responses to questions about carcass disposal can be extracted from the matching sample results. Of 18 matching farms that answered the basic survey and the rendering plant survey, 44% replied similarly in both surveys that they burned or buried carcasses or sent them to rendering plants (proper disposal), 28% replied similarly in both surveys that they left carcasses above ground (improper disposal), and 28% replied dissimilarly on the 2 surveys. Thus, 56% of farmers who had not suffered wolf depredations admitted on either or both surveys that they improperly disposed of carcasses. Nevertheless, all these farms are within 15.2 km (mean of these 56% farms = 6.2 km, range 1.6-15.2 km) of farms that experienced chronic depredations by wolves. If improper carcass disposal were of prime importance in predisposing farms to wolf depredations, one wonders why matching farms did not suffer such depredations.
One possible explanation is that because matching farms held fewer cattle, they may have sustained fewer general losses and thus had fewer carcasses available. Larger farms would generally have more natural losses and thus might have provided a more reliable food source at carcass dumps, thus attracting wolves more often. This interpretation could even be the explanation for why larger farms with more cattle tended to experience wolf depredations. However, the whole subject of carcass disposal as a factor predisposing cattle to wolf depredations remains open.
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