Seeming to skate on its own reflection, a spotted sandpiper comes in low
over the quiet water, wingtips almost touching the surface of the lake.
It alights at the shore and folds its wings. Amid the rounded rocks,
this plain but elegant little shorebird is all but swallowed up.
Teetering constantly on long legs, it sets off along the water’s edge,
pecking here and there, coming closer and closer, never forgetting to
stop and curtsy, as if acknowledging, while hurrying offstage, the
applause of an audience.
As it draws near, several water striders skate away from the shore. A
stonefly, scuttling between two rocks, is deftly speared. So large a
morsel makes the bird pause and rough its feathers, then scamper into
the water to take a drink. Teetering again, it passes in front of me and
continues down the shore, where I soon lose sight of it rounding a rocky
point.
I am sitting at the foot of Lake McDonald, watching the darkness gather
over the valley, seeing the last light slide upward to the tips of the
distant mountains. As daylight dissolves, this long fleet of familiar
peaks seems almost to glide toward darkness, slow and silent as sailing
ships.
The sheet of motionless water stretches many kilometers away between
tree-covered moraines. The water is deep and cold. No emergent plants
line the barren shore. It would seem that no life, except for the single
gull that rests on the water far away, exists in this nearly
thousand-meter-high lake.
■
Considering the great volume of Glacier’s large, deep lakes, the life
they support is indeed meager. A large part of the reason lies with the
nature of their shores, where almost no plants grow. A combination of
factors prevents the development of a lush shoreline growth.
Contoured like bathtubs, these steep-sided lakes exhibit narrow or
non-existent shoreline shallows, which are vital for the production of
rooted plants. Strong wave action and extensive seasonal fluctuations in
the level of these natural reservoirs prevent the development of
emergent water plants in locations where they might otherwise be
expected.
Since sunlight cannot penetrate to the bottom of these deep lakes, they
are deprived of bottom-anchored plants in midlake as well. As a result,
herbivorous animal life must depend almost wholly on algal growth. Wave
action inhibits the spread of free-floating algae by washing much of it
onto the shore. Deep lakes are also low in available oxygen, preventing
the development of bottom decomposers, which would rapidly release
nutrients as they break down the accumulating debris washed into the
lake. Without a steady supply of nutrients, plant growth is retarded.
Since the food chain depends upon green plants, the ability of a lake to
support higher animals such as fish depends upon its ability first to
produce adequate plant growth. The production of one kilo of trout
requires that a lake produce about 1,000 kilos of plants to support 100
kilos of herbivorous invertebrates, which are eaten by 10 kilos of
carnivorous insects, on which the trout feed.
Compared to smaller shallow lakes, which teem with visible life, cold,
deep, nutrient-poor lakes such as McDonald appear to be watery deserts.
Yet because of their great volume—Lake McDonald contains 5 or 6 cubic
kilometers of water—these large lakes do sustain significant numbers of
fish. Of the 22 kinds of fishes found within the park, most are
coldwater species. Trout, whitefish, grayling, suckers, minnows, and
carp fill the roles of herbivore, carnivore, and scavenger. Agile,
highly mobile, and acutely sensitive, fish represent the most successful
total adaptation to the aquatic environment.
Through the stocking of nonnative species, including plantings in
formerly fish-free lakes, the natural aquatic communities of many of
Glacier’s lakes and streams have been permanently modified.
Aquatic food chains are not confined to the water. Ospreys, ducks,
mergansers, otter, mink, and many other semi-aquatic or terrestrial
birds and mammals utilize the plants and animals of the water. In fall,
a remarkable spectacle occurs along the outlet of Lake McDonald.
Attracted to the kokanee salmon concentrations, which run from Flathead
Lake to spawn and die in these clear, shallow waters, bald eagles
collect to exploit the vulnerable fish. In 1977, 444 eagles were counted
in one census. This food resource is also exploited by grizzlies,
coyotes, skunks, gulls, loons, and other animals. On occasion, even
white-tail deer have been observed swallowing salmon!
[Illustration: Sunset]