Wolf Depredation on Livestock in Minnesota
Results of the 1979-80 Approach
During 1979 the FWS received 29 complaints of wolf-livestock problems. FWS personnel confirmed that in 15 of the instances (12 farms) wolves had killed livestock. (More than one complaint was verified at a few farms.) The number of individual livestock claimed lost to wolves in 1979 were 7 cows, 98 calves (remains of only 14 were found), 1 sheep, and 3 chickens. Losses judged by FWS personnel to be wolf kills (verified losses) were 5 cows, 12 calves, 1 sheep, and 1 chicken.
During 1980, 40 complaints of wolf-livestock problems were received. In 26 instances (17 farms) wolves had killed or wounded livestock. The number claimed lost were 10 cows, 45 calves, 73 sheep, 1 foal, and 56 turkeys. Losses verified by FWS personnel as wolf kills were 4 cows, 12 calves, 56 sheep, 1 foal, and 56 turkeys. The major difference between total losses reported and losses verified by FWS personnel were cattle and sheep that could not be accounted for (no remains were found).
The most feasible and objective method of evaluating the effectiveness of the 1979-80 approach is to compare indices to depredations in these years with indices from previous years. Probably the best indicators of the overall seriousness of the depredation problem are the number of farms suffering verified losses within a year, the number and types of animals lost, and the number of complaints verified. Both FWS and MDA records include data that can be used in this evaluation; these records date back to 1975 and 1977.
The number of complaints verified by the FWS and the number of farms where depredations were verified in 1979-80 were within the range of those for other recent years (Fig. 4). Unfortunately, FWS records of the number of livestock claimed lost from 1975 through 1978 are too incomplete to compare with 1979 and 1980 figures; however, the number of livestock on which the MDA paid compensation in 1979 and 1980 was similar to 1977 and 1980 figures (Table 1). Therefore, the extent of the depredation problem seems to have changed little in recent years.
The number of complaints verified and the number of farms where losses were verified by the FWS were slightly higher in 1980 than in 1979 (Fig. 4); a similar increase appeared in MDA figures (Table 1). The increase in verified complaints was due in part to repeated complaints at two farms. A reduction in calf losses from 1979 to 1980 was offset by an increase in sheep losses. Sheep were killed at four farms, two of which were sites of losses before 1980. Although the number of farms sustaining livestock losses has increased slightly since 1977 (Fig. 4), it is not yet possible to determine whether the trend is real.
Although MDA and FWS records of depredations were comparable in both 1979 and 1980, two of the MDA's indices to depredations were higher in both years (Table 1; Fig. 4). The number of claims paid by the MDA was higher than the number of complaints verified by the FWS, and the number of farmers to whom claims were paid was higher than the number of farms where the FWS verified losses. The total number of complaints received by the FWS, however, exceeded the number of claims received by the MDA because complaints sometimes only involved sightings of wolves, whereas compensation claims had to involve an actual loss or claimed loss. The MDA paid compensation for more individual livestock than the FWS considered killed by wolves in 1979 and 1980 because of more lax verification criteria for the State compensation program and because some farmers who filed compensation claims to the MDA failed to complain to the FWS.
Another important consideration in evaluating the overall effectiveness of the 1979-80 approach is the number of wolves killed. Because the wolf is classified as "threatened" in Minnesota, the FWS should minimize the number of wolves it kills for depredation control while still alleviating depredations effectively. Except for 1975, when the FWS suddenly had to assume the control program and was unprepared, the number of wolves captured during control activities in 1979 and 1980 was the lowest in a decade (Fig. 5). In 1979, 15 wolves were captured, but 9 were released as pups; only 6 adults were killed. Of 26 wolves captured in 1980, 5 were released and 21 were killed. The increase from 1979 to 1980 resulted from responding to more complaints (14 vs. 27) and likely also from increased effectiveness of technicians in trapping at farms. The reduction in wolves captured in 1979 and 1980 vs. previous years resulted from more tightly regulated trapping.
The effectiveness of specific depredation-control methods in controlling losses is difficult to evaluate (Griffiths et al. 1978). Insufficient funds were available to attempt actual controlled studies of the several actions taken. In fact, controlled studies may not be feasible because of the sporadic nature of depredations and the small number of farms involved and livestock killed. Results of the taste aversion baiting are still not conclusive.
Although some farmers believed that the blinking highway lights kept wolves away at night, our findings are ambiguous. During a few occasions at a farm in winter 1979-80, tracks of wolves were found in the snow approaching the lights, but there was no indication that wolves had walked past or between lights spaced about 60 m apart. Losses occurred at 4 of 11 farms where lights were up during summer of 1979 and 1980. Wolves killed sheep within 45 m of a light at one farm and 30 m of a light at another in 1980; however, it was impossible to determine whether the depredations occurred at night or during the day when the lights were off. In one of the instances mentioned above, wolves definitely returned and fed from the carcasses at night when the light was functioning, and traveled within 3 m of the light while entering the pasture. Several instances of coyotes traveling between lights were noted, although the time of day was not known. In general the lights seemed more effective in smaller and open pastures than in large wooded ones where it was virtually impossible to surround livestock effectively with them. The same appeared to be true of the flagging.
During 1979 and 1980 our trapping efforts were successful in 22 (54%) of 41 attempts (instances of verified losses in which the FWS responded by setting traps). We found it difficult to correlate the number of wolves removed at a farm with a reduction in the loss rate, as no or few wolves were trapped at some farms, yet these same farms suffered no additional verified losses. In 1979 there were six farms where losses were sustained but no wolves trapped; none of these farms reported verified losses in 1980. Three of six farms where wolves were trapped in 1979 were the scene of losses again in 1980. Also, among 17 farms where wolves were trapped in 1979 and 1980 combined, eight additional losses were verified following trapping. It seems that depredations at some farms may stop even though few or no wolves are removed; at other farms depredations continue despite wolves being captured regularly.
The results stated above, together with observations by FWS personnel from 1975 through 1978, reflect an important distinction among farms where depredations occur. Such farms fall into two broad categories: those with a history of losses, occurring at least once every 3 years (Type I), and those where losses are infrequent, occurring once or twice over a period of several years (Type II). Losses at Type I farms usually result from a depredating pack living nearby and having regular contact with cattle or sheep. At present, about 10 Minnesota farms fall into this category; many other farms may have packs nearby but have very few or no losses. Trapping efforts at Type I farms usually result in wolves being captured.
Losses at Type II farms seem to be caused most often by single, non-territorial wolves that spend little time in one area. Nine of 29 (31%) farms where the FWS trapped in 1979 and 1980 fit this classification. Trapping rarely results in the capture of wolves at these farms. In the Type II situation the depredations usually stop by themselves, probably because the offending wolf soon leaves the area. Trapping serves no apparent useful purpose in such situations, so a short trapping period is appropriate there, especially if there is no evidence that the depredating wolf has remained near the farm.
Even at Type I farms that are visited regularly by packs, depredations are sporadic both between and within years. Only two farms seem to have been the site of regular annual losses since 1975. This indicates that extremely few wolves regularly depend on cattle and sheep for food. Trapping at Type I farms eliminates some of the offending wolves, but usually not all pack members can be trapped. Breeding adults are older and more experienced and thus are the most difficult to capture. Even if the offending pack members are eliminated, other members sharing the depredation tradition may eventually reinitiate the depredations.
When several wolves spend considerable time in a pasture and regularly encounter
cattle and sheep, the potential for depredations is greatly increased. The
opportunity for this is influenced by husbandry practiced at the farm. Thus,
trapping would not be expected to indefinitely alleviate losses at Type I
farms. Nevertheless, FWS records show that removal of three or more members
of a depredating pack was followed by a reduction of losses at 10 Type I farms
during the past 6 years. On the other hand, depredations stopped or decreased
at approximately 13 Type I farms even though 0-2 wolves (
= 1.3) were trapped. Trapping seems to have a positive effect at most Type
I farms, but the extent of trapping that is necessary to reduce losses is
not obvious.
The effect of releasing trapped pups cannot yet be determined; however, among three farms where pups were released in 1979, two suffered losses again in 1980. A pup released at the third was recaptured at a neighboring farm in 1980 following cattle losses.
Conceivably, evaluation of the 1979-80 program should be based on future losses as well as those occurring during these years alone. If too many depredating wolves were left uncaptured, depredations might increase in some areas; however, at present there is no evidence that a successful livestock depredation control program must include taking large numbers of wolves. To do so without capturing the offending ones probably does little to alleviate the problem.
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