Fauna Series No. 7
Isle Royale Mammal History
Methods and Extent of Present Research
Fauna of the National Parks No. 7
The Wolves of Isle Royale
RESULTSTHE TIMBER WOLF AND ITS ECOLOGY
Figure 33Wolf tracks in snow.
The composition of the Isle Royale wolf population
makes possible a reasonably precise count but renders difficult an
absolutely complete census. The main pack, containing 15 to 16 members,
usually was relatively easy to locate. However, groups of three and two,
and lone individuals, also were sighted. (These smaller groups were
difficult to find and keep track of.) Thus, censusing involved finding
and counting the large pack and then trying to locate all other groups.
The wolves' preference for traveling along the Isle Royale shore or on
lakes was most important in the success of the censuses.
Censuses were attempted on the first or second day
after a fresh snowfall, or under the following combination of
circumstances: (1) the known whereabouts of the large pack, and (2) the
discovery of a recent kill made by another pack (thus often allowing the
prompt locating of this pack), and/or (3) the accidental sighting of
other wolves. During censuses, we flew at 300 to 500 feet altitude and
surveyed the entire shoreline and all major lakes for wolves or tracks
(figure 33). Tracks were followed until the wolves were found, if
possible. Undoubtedly, no large packs escaped detection, but perhaps one
or two lone wolves did.
On February 9, 1959, after a fresh snowfall, the
first census was made. A pack of 15 wolves was discovered near McCargo
Cove, a lone wolf at Todd Harbor, and another individual in Rock Harbor.
A search of the rest of the island produced no other wolf sign. However,
on February 23 a pack of 3 was sighted near Five-Finger Point, and a few
minutes later the pack of 15 plus a lone wolf were discovered near
Davidson Island, demonstrating that at least 19 wolves were present. The
extra lone wolf seen February 9 might have been a straying member of the
pack of three. No other wolf sign was seen in 1959 which could
definitely be attributed to any other animals.
In 1960, four groupings of wolves were noticed: 15
(plus a lone wolf which followed this pack closely), 3, 2, and 1. The
two wolves were seen three times, and the pack of three, five times, all
on the same half of the island, but both packs never were observed on
the same day. Therefore, I thought that perhaps the two wolves were part
of the pack of three, and that the single wolf (only noticed once that
year) was the third animal. The total estimate remained at 19 or 20.
Figure 34Tracks of five wolves in sand.
Figure 35Wolf tracks in snow.
Therefore, the 1961 estimate of the number of wolves
present on Isle Royale is 21 and possibly 22. The difference between
estimates in 1960 and 1961 is caused only by the difference in
interpretation of the observations. That the pack of two was not seen in
1959 does not mean it was not present, for during that year even the
pack of three was observed only once, whereas in subsequent years it was
seen many times. I believe that the Isle Royale wolf population has
remained unchanged for the duration of this study. My increasing
familiarity with the island's wolves from one study period to the next
merely has made the last census most precise.
The census in 1961 was complicated by the fact that
the large pack often split up. Nevertheless, this pack still contained
15 animals. Lone wolves and the pack of three again were sighted several
times. This year, however, strong circumstantial evidence indicated that
an additional pack was present, composed of two animals. Although this
never was proved conclusively, general knowledge of the Isle Royale
wolves makes me believe that the group of two animals seen in 1960 and
1961 was not part of the pack of three.
Figure 36Wolf tracks in sand.
Figure 37Wolf tracks near kill.