Significant changes in its bird population are taking place in Yellowstone National Park.
This comes from an article in the July 2 issue of the "National Geographic" magazine. The story illustrates that you cannot change one thing in nature without influence on many other things. Life is one long chain.
It begins 25 years ago when Lake Trout were introduced to Yellowstone Lake. The trout are not native to that lake. They fed — are feeding — on Yellowstone Cutthroat Trout, a native species.
The Lake Trout have at this point eliminated about 90 percent of the Cutthroat, according to the article. The Cutthroats also are present in streams feeding the lake. In early summer, when Grizzly sows have cubs, they depend on those trout for food.
With fewer trout. the bears are preying on Elk calves. Bears now kill more elk calves than the wolves in the park.
Cutthroat Trout are shallow-water fish. Ospreys eat them. Lake Trout are deep-water fish. Ospreys can not use them as food. Most of the nesting Ospreys have abandoned the park for lack of food. In the early 1990s there were 62 documented Osprey nests in the park. In 2017 there were three.
Bald Eagles also ate the Cutthroats. When they could not find enough to meet their needs, the eagles did not leave. Instead, they began to prey on birds.
The park's Trumpeter Swan population is threatened. Eagles are eating young swans.
