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Heard, D.C.
and G.B. Stenhouse. 1992. Herd identity and calving ground fidelity
of caribou in the Keewatin District of the Northwest Territories. 34
pp.
ABSTRACT
A caribou herd is defined as a group of animals that calve in the same
location each year.
Periodic dispersal of large numbers of caribou between herds has
been suggested as a driving force in caribou population dynamics, but
studies of marked animals in Alaska have documented only limited
movement between herds.
Recent increases in the Kaminuriak and Bathurst caribou herds
indicated that massive immigration may have been partly responsible.
In
order to document distribution at calving and fidelity to calving
location, we radio-collared 62 cows on the range of the Kaminuriak and North-eastern
Mainland caribou herds, between November 1984 and June
1985. We
collared 40 more caribou before June 1986 and 10 more before June 1987.
We flew over the entire District of Keewatin listening for radio
collars each June between 1985 and 1988 in an attempt to locate each
collared cow.
The
distribution at calving was such that 3% of Kaminuriak cows (range
0-5%/yr) would not have been included within a calving ground defined
using standard survey techniques.
At Wager Bay, the proportion of cows calving in peripheral areas
averaged 9% (range 0-13%/yr).
Moreover, Wager Bay cows calved at lower densities and the
location of the highest density calving areas varied more between years.
We concluded that standard calving ground survey techniques
adequately defined the Kaminuriak calving ground but failed to do so at
Wager Bay.
We
considered a cow to be unfaithful to its calving location when its
calving location differed by at least 90km between years.
In 1986, 7 of 51 cows (14%) were unfaithful to their 1986 calving
location.
Eight of 50 (16%) were unfaithful in 1987 and 8 of 54 cows (15%)
were unfaithful in 1988.
On average, 85% of cows return to the same location each year to
calve.
In 19 of the 23 instances where calving location changed between
years the cow went from calving in the core of the calving ground to
calving in a peripheral location or the other way around.
In the other 4 instances, 3.6% of all fidelity tests, cows moved
between recognized calving grounds.
Between
1985 and 1988 the combined effects of changes in calving location (4%)
and calving ground survey bias (i.e., excluding between 3 and 13% of the
cows from the census zone) were much less than the change in the number
of cows on the Kaminuriak herd's calving ground between 1980 and 1982
(315%).
Therefore the data do not support the suggestion that immigration
contributed substantially to that increase.
However, our observations describe caribou behaviour only between
1985 and 1988 and do not eliminate the possibility that large scale
dispersal contributed to changes in the number of animals on the
Kaminuriak calving ground in past years.
Because
calving site fidelity was high and similar to what has been observed
elsewhere, the Kaminuriak and North-eastern Mainland caribou herds appear
to be discrete and there is no reason to reject the concept of herd
definition based on calving grounds. The calving ground concept suggests
that Lorillard and Wager Bay must be considered one herd but movements
throughout all of the north-eastern mainland are still too poorly known
to be able to differentiate subpopulations.
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