There was no correlation between the daily area (km
2
) in
which wolves traveled (i.e., prey-searching rate) and log
10
pack size (r
2
= 0.02, df = 44, P = 0.33). Small packs traveled
23 ± 5 (mean ± SE), medium packs 18 ± 5, and large packs
28 ± 4 km
2
/day. Daily area of travel was unrelated to either
moose density (
r
2
= 0.04, df = 44, P = 0.18) or the ratio of
moose numbers to wolf numbers (
r
2
= 0.04, df = 44, P =
0.17). These nonsignificant relations indicate that competi-
tion for prey resources did not influence prey-searching rates
of wolves.
We found no difference in the handling times (number of
days packs spent on kills) between adult moose (n = 65,
2.9 ± 0.17 (mean ± SE) days) and calf-moose kills (n = 35,
2.6 ± 0.22 days). Handling times for adult moose did not
differ (Kruskal–Wallis test,
χ
2
= 5.4, n = 65, P = 0.07) be-
tween small (
n = 17 kills, 3.3 ± 0.19 days), medium (
n = 19,
3.1 ± 0.5 days), and large packs (n = 29 kills, 2.6 ± 0.16 days).
Handling time for moose calves differed with pack size
(analysis of variance (ANOVA), F
[37]
= 3.9, P = 0.03). Small
packs averaged 3.3 ± 0.3 (mean ± SE) days (
n = 16 kills),
medium packs averaged 2.5 ± 0.3 days (n = 8 kills), and
large packs averaged 2.0 ± 0.3 days (n = 29). Caribou kills
(n = 13) were handled for an average of 1.3 ± 0.1 days. We
saw some large packs consume caribou in a few hours, mak-
ing it difficult to accurately estimate caribou handling times.
Large numbers of wintering caribou were available to 4
packs during 11 predation periods. Although caribou greatly
outnumbered moose, packs still killed more moose (n = 40)
than caribou (n = 20). Biomass of the moose killed by each
of these wolves per day was 7.9 ± 0.7 (mean ± SE) kg com-
pared with 2.5 ± 0.6 kg of caribou.
Snowshoe hare availability did not influence the kill rate
by wolves on moose. Hares were abundant during 1990 and
1991, but crashed during winter (Krebs et al. 1995). We
tested for effects of hare availability by comparing KGWD
with log
10
pack size, nested within the periods of presence
and absence of snowshoe hares. Kill rate was not correlated
with hare availability (nested ANOVA model, F
[1]
= 0.12,
P = 0.91).
Both DMK and log
10
days/calf kill were not correlated
with March snow depth (Table 2). Snow depth did not differ
between years (ANOVA, F
[33]
= 0.66, P = 0.63), ranging
from 79 to 94 cm. The vulnerability of moose to predation
by wolves increases when snow depths exceed 90 cm (Peter-
son 1977; Peterson et al. 1984). This snow depth was not
exceeded in most winters.
We estimated consumption with an adjustment for raven
scavenging (RA) and without (NRA). Based on the results of
mock trials in our study area, Promberger (1992) estimated
that ravens could remove 50% of ungulate biomass from
a pair of wolves, 33% from a pack of 6 wolves, and 10%
from a pack of 10 or more wolves. The NRA rate was 8.7 ±
0.9 (mean ± SE) kg/wolf each day, and was negatively
correlated with log
10
pack size (r
2
= 0.40, df = 44, P <
0.0001). Wolves in small packs apparently consumed 12.7 ±
1.5 kg/wolf each day, those in medium packs 7.6 ± 1 kg, and
those in large packs 4.6 ± 0.3 kg.
The RA rate remained correlated with log
10
pack size, but
pack-size differences were reduced (
r
2
= 0.13, df = 44, P =
0.014). Raven scavenging reduced the available biomass to
6.4 ± 0.8 (mean ± SE) kg/wolf each day for small packs,
5.7 ± 0.9 kg for medium packs, and 4.1 ± 0.9 kg for large
packs. The RA rate differed among the three pack-size
classes (Kruskal–Wallis test,
χ
2
= 6.1, df = 2,
P = 0.04).
Predation rate by wolves on moose
Small packs (n = 17 periods) killed 27 ± 2.4 (mean ± SE)
moose each winter, medium packs (n = 12) 35 ± 3.8 moose,
and large packs (n = 14) 46 ± 3.5 moose. We modeled win-
ter predation on moose by applying these rates to packs with
known composition each winter. As wolf packs in the area
increased in number from 14 in 1990 to 24 in 1994 (see Ta-
ble 2 in Hayes and Harestad 2000a), wolves increased their
moose kills from 437 to 1037 (Table 3). For comparison, we
modeled moose predation by applying the grand mean kill
rate by wolves (0.045 moose/day for each wolf) and the
number of wolves alive each winter (see Table 2 in Hayes
and Harestad 2000a). The grand mean method yielded an es-
timated moose kill rate in 1994 that was nearly twice the
pack kill rate (Fig. 5).
We estimated that wolves removed 10–15% of all moose
and 7–16% of moose older than calves during winter (Ta-
ble 3). We found a strong negative relation between annual
wolf density (Table 2 in Hayes and Harestad 2000a) and the
percentage of moose calves alive in March (Fig. 6; r
2
= 0.86,
df = 4,
P = 0.02). We found a similar relation for caribou
calves (Fig. 6; r
2
= 0.80, df = 4, P = 0.04).
© 2000 NRC Canada
Hayes et al.
53
Winter
Total no.
of moose
a
No.
killed
b
% of total
killed
Total no. of
non-calves
c
No. of non-
calves killed
d
% of non-
calves killed
1990
4537
436
0.10
2904
196
0.07
1991
5313
736
0.14
3347
552
0.16
1992
6227
912
0.15
4608
675
0.15
1993
6952
991
0.14
5422
872
0.16
1994
7642
1037
0.14
6801
705
0.10
a
Based on mean moose density (Appendix, Table A1), a total area of 23 000 km
2
, and 75% habitable moose range
(our calculations).
b
Based on the pack kill rate for the winter period.
c
From Table 1 (proportion of non-calf moose seen in March obtained by subtraction).
d
From Table 1 (proportion of non-calf moose killed by wolves obtained by subtraction).
Table 3. Proportions of all moose and of non-calf moose killed by wolves each winter, 1990 through
1994.
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