Visual display of the Aldo Leopold papers : 9/25/10-4 : Species and Subjects


of thousands of ducks, geese, and other water
birds died shortly before Christmas, 1925. No
such outbreak of disease had ever occurred
there before. The water was fresh, and all the
circumstances indicated disease as the cause
rather than poisoning. I visited the area in
March, 1926, and great numbers of wings, feet,
bills, and other fragments remained as evidence
of great mortality.
On the saline flats in and near the delta of
Bear River, Great Salt Lake, Utah, millions
of ducks and other waterfowl have died, at
intervals, of what was believed to be alkaline
poisoning. In 1924, a rise in level of the in-
tensely salt lake waters destroyed many thou-
sands of acres of marsh that afforded feeding
grounds for a host of migrants and nesting
grounds for many resident birds. Since that
time the losses from alkaline poisoning have
been less severe, perhaps because of the fact
that marsh destruction has rendered the area
less attractive to great numbers of birds. The
70th Congress has authorized an appropriation
of $350,000 for the creation of a Federal bird
refuge to embrace about 45,000 acres in this
section. Plans for the construction of a pro-
posed dike system are designed to accomplish
two main purposes. First, to impound fresh
shallow water over the broad marginal mid
flats, thus providing tens of thousands of acres
of excellent feeding grounds and obliterating
the conditions under which the birds died of
alkaline poisoning; and second, to prevent a
re-invasion of the salt lake water that proved
so destructive to marshes in 1924. The ex-
perience of the state and of a local shooting
rl,,h on a smaller scale has shown that sago
pond-weed soon makes a splendid growth in
water so impounded. Construction of the dike
will provide an additional breeding area of wide
expanse but its greatest value will be the pro-
vision of a vast feeding and resting ground for
a host of migrants at a key point in their over-

relation of these animals to their favorite prey
may best be gauged in a region still unmodified
by man. In the forests of eastern Panama,
where conditions are essentially primeval and
food for deer is always abundant, I have been
told by Indian hunters that the numbers of
mountain lions and (leer fluctuate together

through cycles of undetermined length. The
Indians believe that the lions increase where
deer are plentiful until rather soddenly the
deer disappear and the lions are no longer in
In some sections of the West the killing of
mountain sheep is prohibited under state laws,
and although poaching upon them by hunters

The lower end of Blitzen River, disappearing on the dry bed of Lake
Malheur, Oregon, in 1925 and 1926, where thousands of ducks and o'her
birds perished in that year.

land flight.
While predatory animals of many kinds are
recognized as a menace to game, it seems doubt-
ful whether there is a true appraisal of the
extent of their inroads. Mountain lions are
known to feed largely upon deer. The true

is believed to be negligible, little or no increase
is apparent. It seems probable that the nearly
stationary number of such herds is due to the
ravages of predatory animals, although diseases
are known in some cases to play their part.
The increase of mountain sheep introduced on

the National Bison Range from 12 animals in
1922 to 69 in 1927 is a gratifying example of
what may be expected where these splendid
game animals are accorded adequate protec-
tion and epizodtics do not occur.
The case of the mule deer of the Kaibab
Plateau in niorthern Arizona may be cited as

one in which there was a remarkable increase
in numbers in spite of the fact that the control
of predatory animals was only partial. The
mountain lions were reduced to small numbers,
but coyotes continued to take a heavy toll of
the game. From an estimated 3,000 or 4,000 in
1906, when the general area was set aside as a
Federal game preserve, the deer population rose
to an estimated 30,000 (and this was probably
very conservative) in 1924. The summer of
1924 was a season of unusual drought, which
hastened a shortage of forage that was already
threatened. In August thousands of deer were
already much emaciated and by the following
spring the deer had greatly decreased.
The elk of the Yellowstone Park region have
fluctuated widely in numbers, largely owing to
starvation during winters of unusual severity.
Although limited killing is permitted under the
state law, the heads have been known to be
about double in size in 4 years following such
winters, after which the rate of increase seems
to be markedly reduced.
Sufficient food and water and adequate pro-
tection from enemies are essentials if game is to
thrive and be maintained on a satisfactory scale,
hut comparative freedom from parasites or dis-
ctses, especially those becoming periodically
oizootic, and in waterfowl freedom from what
are believed to be mineral poisons, is of vital
importance. Parasitism may account for the
comparative rarity of some animals, including
various members of the weasel family that es-
pecially in the warmer regions are apparently
able to obtain abundant food and so far as
known have few natural enemies. Squirrels and
many other animals locally reach excessive
numbers, from which they sharply decline, often
for undetermined reasons. In some instances,
it is undoubtedly failure of an ample food sup-

Photo by  courtesy, of  National  Park  > vio c
Deer at Mammoth Hot Springs, Yellowstone National Park.

ily, in others, disease, in still others, a com-
bination of factors may be operative. Epizootics
evidently provide the final check to overabun-
dance in all wild life, and correspond to epi-
demics in man.
Leading elements bearing usually in combina-
tion upon the fluctuation in numbers of game
and all wild life may be summarized as fol-
1. Game (and all wild life) has certain
biological requirements, imperfectly understood,
which must he met if it is to be maintained in
satisfactory numbers. A natural balance, never
perfect, has been overturned and proper game
administration should take its place.
2. Sufficient suitable food and water at all
seasons is vital, and if these are afforded rapid
increases may be expected as long as other con-
ditions are favorable. Inevitably, however, there
comes a time when increasing numbers have
outrun the food supply, or other changing con-
ditions apply a definite check.
3. The provision of suitable cover and of
adequate protection from predatory animals and
from over-hunting by man are obvious essen-
tials, the lack of which has led to extermination
over vast areas where game should remain
4. The final natural check to over-abun-
dance where others fail in any species seems to
be parasitism, or the development of epizootic
disease. A few parasites or disease organisms
may remain innocuous or fatal only to a few
individuals, but the ever-closer contacts result-
ing from over-population favor mass infection.
Under such conditions, disease organisms would
themselves tend to mount inordinately in num-
bers and possibly increase in virulence. At any
rate, epizootics as in the rabbit, grouse, and
many other wild species, correspond to such
human epidemics as influenza and bubonic
plague, which uncontrolled reduce populations
at a rapid rate. Human bubonic plague trans-
mitted through fleas from rats exemplifies the
complexity of biological contacts everywhere.
In proportion as we gain knowledge of all
the factors bearing upon fluctuation in num-
bers, and as we are able to apply the knowledge
acquired, we shall be successful in the admin-
istration of the game and other wild life assets
essential to our well being.