Ecological Studies of the Timber Wolf in Northeastern Minnesota Part 5

"At 3:00 p.m. while we were following wolf 1051 by aircraft in above location, we saw a deer running very quickly on top of the crusted snow and then stand and watch its backtrail.

About 1-1/2 minutes later we saw 1051 running along the same route. We did not see when the deer fled again, but saw it running about 100 yards from the wolf and doubling back paralleling its original route. When the wolf got near the approximate doubling-back point, he lay down and rested for about 5 minutes. The deer continued fleeing for about 350 yards, stopped, and for several minutes faced its backtrail.

The wolf finally continued on in his original direction, giving up the chase.

"At 4:30 p.m.--1-1/2 miles S. of Central Lakes, Minnesota--Wolf 1051 had come to within 100 yards of [four-lane] Highway 53 and was hesitant to approach it.

Several cars were going by in both directions. Thus the wolf headed S. parallel with the highway about 150 yards E. of it.

"Suddenly two deer, which we had noticed S. of the wolf earlier, fled across the highway. The wolf soon got to the point where they crossed, hesitated about a minute and then ran across. No cars came at that time.

"We could not always see the deer or the wolf when W. of the road because there were several patches of evergreens. The wolf did head straight W. after crossing the road. Then about 250 yards W. of this point we saw a deer come out onto an old woods road which lay in a N.W.-S.E. axis. The deer ran N.W. on the road and then we saw the wolf where the deer had come out onto the road. While the deer ran N.W., the wolf cut into the woods to his right, N.E. We could not see it then but presumed it was running N.W. paralleling the road.

"After the deer had run about 50 yards up the road, it also headed N.E. into the evergreens. Within a few seconds it fled right back out and started S.E. down the road. The wolf was about 50 feet behind it and began gaining.

"When the deer got back to where the wolf had headed into the woods from the road before, it also headed N.E. into the woods. The wolf was then about 20 feet away and the deer was headed N. around in a circle with the wolf closing in on the outside. The wolf did not emerge from the evergreens for at least 15 minutes, nor did we see the deer, so I presume the wolf killed the deer. [But see entry for April 1.]

"1 April 1969. Dan Frenzel and I searched the area described on March 27 for 1 hour and found no sign of a kill. Old wolf tracks were seen, but only a single wandering track. No concentration such as usually seen at kills. Best conclusion is that 1051 did _not_ kill the deer where seen from the air March 27."

We also saw 1055 and her a.s.sociate actually kill a deer, on February 6, 1969, but we did not realize what was going on and it happened so fast that we only saw a wolf rushing and biting at the front end of the downed animal. The chase had to have lasted only a few seconds.

In addition to the above direct observations, we also were able to piece together from tracks in the snow the chase and successful encounter between a single wolf and a deer in two instances. In the first case, on January 25, 1967 (11:50 a.m.), we arrived at the scene (near Grub Lake, just N. of s...o...b..nk Lake) within an hour of the encounter, and the wolf was still feeding on the deer, which had been a 2-1/2-year-old female. Mech examined the area from the ground and made the following observations:

"The deer had come S.W. down the middle of the lake at a fast walk, turned around, backtracked a few yards and headed to the N.W. sh.o.r.e of the lake. Meanwhile a wolf had come at a trot along the deer's track, but it had cut to the N.W.

sh.o.r.e about 50 yards N.E. of where the deer had. When still on the ice about 15 feet from sh.o.r.e, the wolf began running as evidenced by his long bounds. He continued running inland about 50 feet from sh.o.r.e toward the deer. The deer had walked inland from the sh.o.r.e and may have stood there about 25 feet from sh.o.r.e. Suddenly it had bounded away. The bounding wolf track was in the same trail as the deer's for about 25 yards but then it paralleled the deer's about 5 feet away on the inland side. After about 125 yards from where the deer flushed, the deer was pulled down. It was _not_ on its side but rather had sunk into the snow in more-or-less of an upright position.

"Apparently the deer had just about reached the sh.o.r.e when the wolf noticed it, and it detected the wolf. At this time the wolf must have been up the sh.o.r.e about 50 yards where his tracks first showed he began bounding. There was no sign that the wolf had spotted the deer on the lake and had tried to cut it off from sh.o.r.e by running inland along the sh.o.r.e and then waiting for the deer to come inland. Once the wolf had begun bounding, he continued until he pulled the deer down.... Sign showed that the deer dropped within about 20 feet of where she had begun bleeding."

The second case involved a 5-1/2-year-old buck, No. M-28, which had arthritis of his right hind foot and probably had defective gait (see Mech and Frenzel p. 35). The attack took place on Ba.s.swood Lake on February 2, 1967, and excerpts from field notes by Mech follow:

"A single wolf had killed this deer after chasing, following, or tracking the deer about 3.75 miles. The deer's last 350 yards was a fast walk--the tracks were one in front of the other and about 2 feet apart, and there was no leaping or bounding. Same with the wolf--a fast trot.

"Where the tracks came together, the deer apparently had fallen, but there was no blood. From there, the deer dragged its feet or the wolf for about 25 feet and then went down again. The wolf circled the deer, and for the next 150 feet, the 2 animals had fought or scuffled and then the deer had gone down where we found it.

"The 4-mile persistence of this wolf--whether tracking, following, or chasing the deer--is remarkable [compared with most chases] and makes me believe the wolf had good reason to believe it could kill the deer."

Our observations of wounds on fresh kills confirm the following description by Stenlund (1955, p. 31) of the location and manner of attack of wolves on deer: "No evidence of hamstringing of deer was found on freshly killed carca.s.ses, although the possibility does exist.

Usually deer are run down from behind, the wolf or wolves biting at the hind flanks and abdomen, or at the hind flanks and head region simultaneously."

On each kill, all the flesh and much of the skin and bones were eaten, at least during the winters of 1966-67 and 1967-68. This was also true during December 1968 and much of January 1969. However, during February and March 1969 when an unusual acc.u.mulation of snow had built up, most of the kills were only partly eaten (see Mech _et al._, page 51). In previous years deer freshly killed by single wolves were sometimes found with only a few pounds of flesh or viscera missing. However, in each case the carca.s.ses were almost completely cleaned up within a few days, often by packs to which the single wolves may have belonged (Mech 1970).

Usually the first parts of a carca.s.s to be eaten are the hams and part of the viscera from the coelomic cavity. In one case where a wolf was interrupted while feeding it was apparent that the animal had been stripping the omental fat from the carca.s.s. This may be the wolf's favorite part of a deer, for the stomach of one wolf that we examined in January 1967 contained nothing but such fat.

The average consumption and kill rate of deer by wolves has not yet been determined, but we have some information bearing on the subject.

Because our data were obtained during a winter of unusually deep snow, and it was obvious that wolves were killing more deer than they could eat at the moment (see Mech _et al._, page 51), our figures should be considered much higher than average. However, they should be useful in that they probably represent the maximum kill rate not only throughout the year but also throughout a period of many years.

By observing each of our radiotagged wolves whenever possible and noting whether or not it was feeding on a kill, we learned that our wolves generally remained close to their kills for periods of from 1 to 7 days, depending on how recently they had eaten (fig. 32). Thus, when a wolf was found at a new location each day, the a.s.sumption could be made that the animal did not currently have a kill.

[Ill.u.s.tration: _Figure 32.--Periods spent by radiotagged wolves and their a.s.sociates feeding on kills judged to be their own. This does not include periods when they were known to be feeding on carrion._]

We a.s.sumed that wolves found at fresh kills (fig. 33) had made them unless there was evidence to the contrary as with 1053, the scavenger.

When a wolf was found at one location for several consecutive days but could not be observed, we a.s.sumed it was feeding on a kill, since whenever wolves were observed remaining in the same location for several days they were seen feeding. Thus a range of possible number of kills per wolf was determined, with the lower limit being the known minimum and the upper limit the possible maximum. When more than one wolf fed on a kill, as with the pack, the figures were calculated on a per-wolf basis.

[Ill.u.s.tration: _Figure 33.--Radiotagged wolf (upper left) found at kill (lower right). (Photo courtesy of L. D. Frenzel.)_]

In this way we obtained data on a total of 468 wolf-days and found a total kill of 35 to 48 deer (table 7). This averages out to a kill rate of one deer per 10 to 14 days per wolf. The figure varied considerably among individuals--1051 had the highest rate of one kill per 6.3 to 7.2 days, and each wolf in 1059's pack had the lowest rate (except for 1053, the scavenger) of one deer per 14.0 to 18.0 days.

It is significant that the pack of five wolves had a lower kill rate per wolf than did single wolves and pairs. This is explainable because the ability of wolves to kill deer during early 1969 was much greater than usual (see Mech _et al._, p. 51). Thus single wolves probably could kill deer just as easily as could packs, but they did not need to share them. This differs markedly from the situation on Isle Royale, where lone wolves usually feed only on moose remains left by packs (Mech 1966a, Jordan _et al._ 1967).

That lone wolves had more of a food surplus than those in the pack is confirmed by the figures on the average number of days that the various wolves fed on kills (table 7). Wolf 1051 spent an average of only 2.2 to 2.4 days feeding at each of his kills, whereas 1059's pack of five spent an average of 5.8 to 7.5 wolf-days at each kill. Further confirmation is found in the fact that even when most wolves were leaving their kills partly uneaten, a pack of 8 to 10 wolves (probably that to which 1057 belonged) was seen completely devouring a kill.

_Table 7.--Kill rate of deer by radiotagged wolves and their a.s.sociates_

#: _Number_

-------------------------------------------------------------------------- Wolf-days Wolf Wolf-days Wolf-days Wolf-days feeding # Wolves Dates of data Kills per kill[14] feeding per kill -------------------------------------------------------------------------- # # # Mean # # Mean #

1051 1 Nov. 26 to 101 14-16 6.3-7.2 33-40 2.2-2.4 Apr. 3

1053[15] 1 Dec. 14 to 75 2-3 25.0-37.5 9-18 4.5-6.0 Mar. 27

1055 1-2 Jan. 9 to 61 4-9 6.7-15.0 13-25 2.8-3.3 Mar. 14

1057 1-13 Jan. 24 to 51 5-7 7.3-10.2 25-33 4.7-5.0 Feb. 28

1059 5 Jan. 25 to 180 10-13 14.0-18.0 75 5.8-7.5 Mar. 14 -------------------------------------------------------------------------- Summary 22 Nov. 27 to 468 35-48 [16]9.8-13.4 145-181 [17]3.8-4.1 Apr. 3

Before 142 7-9 [18]15.7-20.3 39-56 5.1-5.6 Feb. 1

After 326 28-39 8.4-11.6 106-125 3.2-3.8 Jan. 31 --------------------------------------------------------------------------

FOOTNOTES:

[14] Kill rate per wolf.

[15] Figures for this animal are so low because she was basically a scavenger.

[16] Average kill rate per wolf for all radiotagged wolves and their a.s.sociates, derived by dividing total number of wolf-days by total number of kills.

[17] Average number of days that each wolf spent at each kill, derived by dividing total number of wolf-days spent feeding by the total number of kills.

[18] This figure probably is the closest to the actual kill rate during most winters.

Therefore it is probable that the kill rate per wolf for members of the pack of five is much closer to the usual average winter kill rate. It can still be considered higher than the usual winter rate, however, because this pack also was leaving some of its kills partly uneaten.

A reasonable approximation of the average kill rate during most winters would be the rate found for our radiotagged wolves before February 1, because the relations among the wolves, the deer, and the snow during that period were not unlike those of most winters. The average kill rate per wolf before February 1 was estimated at one deer per 15.7 to 20.3 days.

After this period, the rate increased to about one deer per 8.4 to 11.6 days, and an estimated 50 percent of the available food was left uneaten (see Mech _et al._, page 51). This implies that the kill rate during February and March was about twice as high as usual. On this basis, the usual kill rate would be estimated at one deer per 16.8 to 23.2 days, which checks well with the rate found before February (one deer per 15.7 to 20.3 days). Thus we feel that an estimated kill rate of about one deer per 18 days per wolf is a close approximation of the average kill rate for most winters. This is about 50 percent less than the kill rate of one deer per 4 days estimated by Stenlund (1955) for two packs of three wolves (one deer per 12 days per wolf). However, it compares favorably with the actual kill rate of one deer per wolf per 17.6 days found for a pack of eight wolves in Ontario.[19]