In 1916 the kokanee salmon, a small, land-locked form of the Pacific
coast species, was planted in the Flathead drainage. With the first
planting augmented by additional stockings, the fish thrived in
cold, deep Flathead Lake, and, to a lesser extent, in Lake McDonald.
The salmon fed almost exclusively on zooplankton.
By the mid-1930s, salmon runs were becoming established. The outlet
of Lake McDonald provides an ideal spawning site for the salmon. The
fast-flowing water is clear, cold, and shallow, and the creek bed is
gravelly.
Averaging 0.3 meters in length and weighing less than a half-kilo,
the 4-year-old adult salmon cease feeding and begin to migrate. Many
thousands swim the 100 kilometers from Flathead Lake to McDonald
Creek. Males appear in the creek first, arriving in late September,
and are soon followed by the females.
Using her tail to dig a redd (a shallow nest depression), the female
deposits about 650 eggs. After fertilization by the male, the eggs
are covered over. The adults die within three weeks after spawning,
their bodies exhausted from the rigorous migration journey and the
weeks-long lack of sustenance.
Egg fatalities are high, due to stream erosion and disturbance by
other spawning salmon. Hatching in late March, the fry work their
way out of the gravel and migrate downstream.
Attracted to the 75,000-150,000 salmon concentrated in a 3-kilometer
stretch of shallow water, bald eagles begin gathering at McDonald
Creek in October. It is not known where the eagles come from or
where they go after the spawning run. Glacier has fewer than 20
summer-resident bald eagles, and these are distributed among the
remote lakes of the North Fork area.
In 1939, 37 bald eagles were counted along the creek. By 1969, 373
were reported, representing approximately 10 percent of that year’s
estimated winter population for the contiguous United States. Since
1960, the count has averaged 240 birds. (In 1977 there were 444.)
Eagles feed by swooping down to pluck salmon from the water or by
wading out to grab a fish stranded on a shallow riffle. An eagle may
consume as many as six fish a day. Immature birds are not as adept
at catching fish and may harry adults or other immatures into
releasing their catch.
[Illustration: From its vantage point, this mature bald eagle
examines the waters of McDonald Creek. Average weight is 5.7
kilograms; average wingspan is 2.2 meters. Females are slightly
larger than males.]
[Illustration: This immature bald eagle lacks the familiar white
head and tail of the adult birds. It will not acquire those markings
until it is several years old.]
[Illustration: Breeding male and female kokanee salmon are easily
distinguishable; as spawning time approaches, they change
appearance. The dark gray backs turn red; heads become green, and
the males develop humped backs and hooked jaws.]
[Illustration: Swooping upward with a fish, a mature eagle heads for
a convenient perch to consume its catch. A strategically located
tree may contain 30 birds.]