EBB AND FLOW OF ANIMAL LIFE
Throughout this voyage we were struck by the rarity of some sorts
of animals and the continual remarks that three, five, or six years
ago these same sorts were extremely abundant; and in some few cases
the conditions were reversed.
For example, during a week spent at Fort Smith, Preble had out a
line of 50 mouse-traps every night and caught only one Shrew and
one Meadowmouse in the week. Four years before he had trapped on
exactly the same ground, catching 30 or 40 Meadowmice every night.
Again, in 1904 it was possible to see 100 Muskrats any fine evening.
In 1907, though continually on the lookout, I saw less than a score
in six months. Redsquirrels varied in the same way.
Of course, the Rabbits themselves were the extreme case, millions
in 1904, none at all in 1907. The present, then, was a year of low
ebb. The first task was to determine whether this related to all
mammalian life. Apparently not, because Deermice, Lynxes, Beaver,
and Caribou were abundant. Yet these are not their maximum years;
the accounts show them to have been so much more numerous last
year.
There is only one continuous statistical record of the abundance
of animals, that is the returns of the fur trade. These have been
kept for over 200 years, and if we begin after the whole continent
was covered by fur-traders, they are an accurate gauge of the
abundance of each species. Obviously, this must be so, for the whole
country is trapped over every year, all the furs are marketed, most
of them through the Hudson's Bay Company, and whatever falls into
other hands is about the same percentage each year, therefore the
H. B. Co. returns are an accurate gauge of the relative rise and
fall of the population.
Through the courtesy of its officials I have secured the Company's
returns for the 85 years--1821-1905 inclusive. I take 1821 as the
starting-point, as that was the first year when the whole region
was covered by the Hudson's Bay Company to the exclusion of all
important rivals.
First, I have given these accounts graphic tabulation, and at once
many interesting facts are presented to the eye. The Rabbit line
prior to 1845 is not reliable. Its subsequent close coincidence
with that of Lynx, Marten, Skunk, and Fox is evidently cause and
effect.
The Mink coincides fairly well with Skunk and Marten.
The Muskrat's variation probably has relation chiefly to the amount
of water, which, as is well known, is cyclic in the north-West.
The general resemblance of Beaver and Otter lines may not mean
anything. If, as said, the Otter occasionally preys on the Beaver,
these lines should in some degree correspond.
The Wolf line does not manifest any special relationship and seems
to be in a class by itself. The great destruction from 1840 to 1870
was probably due to strychnine, newly introduced about then.
The Bear, Badger, and Wolverine go along with little variation.
Probably the Coon does the same; the enormous rise in 1867 from
an average of 3,500 per annum. to 24,000 was most likely a result
of accidental accumulation and not representative of any special
abundance. Finally, each and every line manifests extraordinary
variability in the '30's. It is not to be supposed that the
population fluctuated so enormously from one year to another, but
rather that the facilities for export were irregular.
The case is further complicated by the fact that some of the totals
represent part of this year and part of last; nevertheless, upon
the whole, the following general principles are deducible:
(a) The high points for each species are with fair regularity 10
years apart.
(b) In the different species these are not exactly coincident.
(c) To explain the variations we must seek not the reason for the
increase--that is normal--but for the destructive agency that ended
the increase.
This is different in three different groups.
First. The group whose food and enemies fluctuate but little. The
only examples of this on our list are the Muskrat and Beaver, more
especially the Muskrat. Its destruction seems to be due to a sudden
great rise of the water after the ice has formed, so that the Rats
are drowned; or to a dry season followed by severe frost, freezing
most ponds to the bottom, so that the Rats are imprisoned and starve
to death, or are forced out to cross the country in winter, and so
are brought within the power of innumerable enemies.
How tremendously this operates may be judged by these facts. In
1900 along the Mackenzie I was assured one could shoot 20 Muskrats
in an hour after sundown. Next winter the flood followed the
frost and the Rats seemed to have been wiped out. In 1907 1 spent
6 months outdoors in the region and saw only 17 Muskrats the whole
time; in 1901 the H. B. Co. exported over 11 millions; in 1907,
407,472. The fact that they totalled as high was due, no doubt, to
their abundance in eastern regions not affected by the disaster.
Second. The group that increases till epidemic disease attacks
their excessively multiplied hordes. The Snowshoe-Rabbit is the
only well-known case today, but there is reason for the belief that
once the Beaver were subjected to a similar process. Concerning the
Mice and Lemmings, I have not complete data, but they are believed
to multiply and suffer in the same, way.
Third. The purely carnivorous, whose existence is dependent on the
Rabbits. This includes chiefly the Lynx and Fox, but in less degree
all the small carnivores.
In some cases such as the Marten, over-feeding seems as inimical
to multiplication as under-feeding, and it will be seen that each
year of great increase for this species coincided with a medium
year for Rabbits.
But the fundamental and phenomenal case is that of the Rabbits
themselves. And in solving this we are confronted by the generally
attested facts that when on the increase they have two or three
broods each season and 8 to 10 in a brood; when they are decreasing
they have but one brood and only 2 or 3 in that. This points to some
obscure agency at work; whether it refers simply to the physical
vigour of the fact, or to some uncomprehended magnetic or heliological
cycle, is utterly unknown.
The practical consideration for the collecting naturalist is this:
Beaver, Muskrat, Otter, Fisher, Raccoon, Badger, Wolverine, Wolf,
Marten, Fox reached the low ebb in 1904-5. All are on the upgrade;
presumably the same applies to the small rodents. Their decacycle
will be complete in 1914-15, so that 1910-11 should be the years
selected by the next collecting naturalist who would visit the
north.
For those who will enter before that there is a reasonable prospect
of all these species in fair numbers, except perhaps the Lynx and
the Caribou. Evidently the former must be near minimum now (1909)
and the latter would be scarce, if it is subject to the rule of the
decacycle, though it is not at all proven that such is the case.