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GLACIER National Park |
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Bald Eagles and Kokanee Salmon: A Recent Gathering 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.  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.  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.  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.  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. |
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Last Modified: Sat, Nov 4 2006 10:00:00 pm PST |
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