2. Almost all predators fall into one of two groups: either they are similar in size
to their prey and can challenge it one-on-one, or they are smaller than their
prey and therefore must hunt in groups. Wolves fit into the second category.
They are a group hunter preying primarily on animals much larger than
themselves. Although a single wolf may be able to kill even an adult moose,
caribou or elk, it is much safer, easier, and more reliable for several animals
to do the job.
3. The number of wolves in a pack varies greatly and it
is interesting to contemplate the reasons for such
variability. A pack may have between 2 to 30 wolves
(the average is about 10), but may even reach 36
with mostly related wolves. Red wolves are less
social than gray wolves and usually form packs of
just three or more (the mated pair and offspring).
Packs are formed when two wolves of the opposite
sex (who may have dispersed from their natal packs)
develop a bond, breed, and produce a litter of pups.
These pups, particularly with gray wolves, will
become the future aunts and uncles to any further
offspring of their parents. Packs, or families, are
comprised of mostly related wolves.
4. There appear to be four factors affecting pack size, all of which stem
from an ecological basis and have resulted in various behavioral
adaptations in the wolf.
These are:
(1) the smallest number of wolves required to locate and kill prey
safely and efficiently.
(2) the largest number of wolves that could feed effectively on any one
particular prey.
(3) the number of other pack members with which each wolf could form
social bonds.
(4) the amount of social competition that each wolf in the pack could
accept.
5. The fact that wolves do live in packs and kill prey much larger than
themselves suggests that the first factor is operating. During the evolution of
pack formation, those ancestors of wolves who hunted together tended to
survive longer than nonsocial wolves and, consequently, produced more
pups with similar social tendencies than the nonsocial wolves (as behavior is
partly genetic and partly what is learned in the environment). However, it
appears that this factor operates only generally because packs vary greatly
in size, and because large packs may not operate as efficiently as possible.
Within a larger pack, rarely is the whole pack in on the kill and, usually, only
few animals actually come in contact with the prey while other individuals
may only be important in helping to locate, chase, or harass the prey. Larger
packs might also split up temporarily and hunt in smaller groups.
6. The second factor that seems to affect pack
size is the amount of prey available to feed
the all the wolves in the pack. A pack might be
so large that, after all the highest ranking
members had finished eating, there wouldn't
be anything left for the subordinates. In such a
situation, hungry ones would go off to hunt
again. This factor would limit pack size if other
factors did not. Even so, other factors do
operate as well, for most packs contain fewer
members than would seem necessary. In
other words, most of the time there is enough
food left over from a kill which could allow for
bigger pack size than what usually occurs.
7. Gray wolves move and hunt mostly at night,
especially in areas populated by humans and during
warm weather. The main prey are
large herbivores such
as deer, elk, moose, bison, bighorn sheep, caribou,
and musk oxen, which they chase, seize, and pull to
the ground. Beavers and hares are eaten when
available, and wolves in western Canada even fish
for Pacific salmon
8. It appears that the above two factors act only as secondary controls. Actual
pack size appears more regulated by the third and fourth factors, which are
the two social factors. Wolves possess a high potential for forming social
bonds, and the social-attachment factor would tend to increase the number
of wolves in a pack.
It probably accounts for the large
packs that contain more members
than necessary. However, the larger
the pack the greater the competition is
for important resources, such as food
and mates.
9. There is also more competition for
leadership and dominance the larger the
group gets. When competition becomes
too tense, pack organization can be
detrimentally disrupted. In these cases
the pack cannot function efficiently and
some members are forced to leave.
Apparently, it is this social-competition
factor that limits the number of wolves in
a pack to less than what could feed
effectively on a prey animal. Dispersing
wolves go off, find a mate and form their
own packs.
10. There have been two other hypotheses proposed regarding the number of
members in a wolf pack. One of these hypotheses indicates that variation in pack
size is linked to the type of habitat the wolves reside in. All of the wolf species
living in larger groups are found in open vegetation. This makes sense because
in order to hunt cooperatively the animals must fan out, maintain contact with
other individuals, and adjust positions during pursuits. Such behaviors could not
occur in a dense habitat. This provides one reason why red wolves would form
smaller packs than the gray wolves, as red wolves tend to occupy denser
habitats than gray wolves. The second hypothesis states that among predatory
species, population group size increases with prey size. The more a pack
depends on large ungulates (such as moose, caribou, and deer), the larger the
pack becomes, and the more cooperation between members is required.
11. Both of the above hypotheses are probably occurring together, just as the
four factors mentioned earlier are playing a part in wolf pack size. Proposing
one hypothesis, or factor, does not exclude the other. There may even be
more reasons yet to be discovered. The ecological pressures placed on
wolves, indeed all living things including humans, are very complex and are
always changing and unfolding. An attempt to understand certain aspects of
behavior, such as why wolf packs vary in size, must always include an
account of a multitude of ecological factors, for it is in this way that we can
only hope to understand why animals behave the way they do.
