Northern Prairie Wildlife Research Center
During 1987-89 an additional 209 complaints of depredations on livestock were received, bringing the total for 1975-89 to 809 (Table 3). An additional 127 complaints were verified, bringing the 15-year total to 455. Verified complaints for 1987-89 averaged 42 per year, at an average of 35 farms (0.51% of producers, assuming 6,800 farms with livestock). Recalculation of long-term (1975-89) averages, with the new data included, revealed 32 verified complaints per year at 24 farms (0.33% of producers, assuming 7,200 farms with livestock). These figures represent increases of 6.7% and 14.3% over previous long-term averages for verified complaints and farms affected.
Cattle, sheep, and turkeys continued to be the livestock most commonly killed; verified losses of these livestock averaged 32, 41, and 1,213, respectively, per year during 1987-89, compared with 23, 49, and 173, respectively, for 1979-86. Annual verified losses of each species were within the range of previous years, except that cattle reached a 14-year peak in 1989, and the number of turkeys killed in 1987 and 1989 far exceeded losses of any other years (Table 1). Compensation payment by the Minnesota Department of Agriculture in 1989 exceeded any previous level because of high losses of cattle and turkeys in the same year (Table 3). Annual payments averaged $10,774 higher in 1987-89 than during the earlier period.
A reexamination of the depredation indices (Fig. 3) for long-term trends confirmed that an increase was occurring. Simple linear regression of the number of verified complaints on time for 1976-89 indicated a significant positive trend (r = 0.600, P = 0.012), and an increase (average of + 1.84 per year) was noted in the number of farms having verified complaints (r = 0.758, P < 0.001). The number of complaints also increased significantly (average, 3.02 per year) from 1976 to 1989 (r = 0.678, P = 0.004). In the previous analysis that extended through 1986, the unusual year of 1981 had held down significance levels for some indices regressed over time; an increasing trend in 1987-89 caused all variable indices to show significant long-term increases (Fig. 3).
Inclusion of the 1987-89 data led us to modify our conclusion about the relation between WSI and numbers of verified complaints. For 1975-86, a significant negative correlation had been shown for simple linear regression of WSI and verified complaints (r = -0. 7 0 1, P = 0. 0 16). However, the relation over 1975-89 was not significant (r = - 0.422, P = 0.133). Evaluation of the relative effects of WSI and year on annual numbers of verified complaints over the 14-year period yielded different results. The new analysis did not support a relation between WSI and verified complaints (F1,11 = 2.40, P = 0.150). When the effect of WSI was accounted for, there was evidence of a time trend in verified complaints (F1,11 = 6.21, P 0.030). Also, when the effect of WSI was accounted for, the addition of the time variable accounted for an additional 62% of the total variation explained (18% previously). However, when the effect of time was accounted for, the addition of WSI accounted for only 24% of the total variation explained (68% previously). This difference in results was largely the result of inclusion of 1989, a highly unusual year in the data set (1987 was almost as variant). The year 1989 had the second highest number of verified complaints, even though it was preceded by the second most severe winter. We do not conclude that a relation between winter severity and verified complaints through 1986 was erroneously identified. Instead, we propose that the relation may have changed recently because of new variables affecting the level of livestock depredations. One such variable, strongly suspect, is an increase in number of wolves in agricultural areas, which may mean higher losses than before, independent of winter severity.
The distribution of verified complaints in 1987-89 was basically the same as in previous years, and several farms where losses occurred in previous years again experienced losses (Figs. 6c and 6d). However, in 1989 we received more complaints from the northwestern and southwestern fringe of the Minnesota wolf range, likely indicating range expansion or population establishment in those areas. The total area over which depredations occurred in 1987-89 was 59,733 km2, Compared with 56,827 km2 in 1981-86. A few depredations occurred in Zone 5 in west-central Minnesota (Fig. 6c), and the geometric center of the depredation sites shifted 24.1 km to the west-southwest. These findings are consistent with the recent conclusion that the Minnesota population increased from about 1,235 in 1979 (Berg and Kuehn 1982) to 1,550-1,750 in winter 1988-89 (T. K. Fuller, personal communication).
Corresponding to an increase in depredations in 1987-89 (especially 1989) has been an increase in the number of wolves taken in control activities-apparent in 1988-89 (Fig 7). In 1989, 85 wolves were captured and 75 killed. For the period 1975-89, 641 wolves were captured and 445 killed or otherwise removed during control activities.
Evaluation of the depredation problem, in light of 1987-89 trend data, conclusively revealed a long-term increase in wolf-livestock conflicts in Minnesota. Such an increase had been suspected. It was suggested by a significant increase in the number of complaints received and farms with verified complaints, but not in the number of verified complaints (which we considered the best index).
Our concern about an increasing trend in turkey losses in the northwestern counties has been substantiated. Our suggestion that preventive control be exercised in certain parts of Wolf Management Zone 5 seems even more valid now. Further, our belief that the number of wolves taken to control the problem in 1979-80 might not be sufficient seems warranted. As before, most wolves that live near livestock do so without initiating depredations. However, an increasing wolf population can only be expected to bring a corresponding increase in conflicts over the long term, particularly when most of the increase can only be at the fringe of the wolf's range (where farm density is higher), rather than at the core. Although the 1989 level of conflicts could have followed a decline pattern, as happened after the 1981 peak, it did not. In fact, depredation indices for 1990 were higher than for 1989, further supporting an increasing trend in wolf-livestock conflicts brought about by an increasing wolf population (W. J. Paul, unpublished data). This upswing in indices underscores the need for improved management practices, research, and a responsive control program, as recommended from analysis of the 1975-86 data.