Significant changes in the bird population are taking place in Yellowstone National Park.
I learned this 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 are present in streams feeding the lake. In early summer, when Grizzly sows had cubs, they depended on those trout for food.
Without the trout the bears began to prey on Elk calves. Bears now kill more of those than do the wolves in the park.
Cutthroat Trout are shallow-water fish. Ospreys ate them. Lake Trout are deep-water fish. Ospreys could 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.
Common Loons are under attack, the eagles hunting not only chicks but also adults.
The same problem exists for the park's small colonies of Caspian Terns, American White Pelicans, and California Gulls. The eagles also take Double-crested Cormorants.
Canada Geese in recent years have established a growing population in the park. There are plenty of goslings to eat. This has not reduced predation of other birds, according to park officials quoted in the story. The goslings simply are helping the population of eagles grow, providing more eagles.
There is fear than other bird species found in the park also will see decline caused by eagle predation.
Shooting the eagles would be a solution, but unthinkable.
The current solution is to remove the Lake Trout to give the Cutthroat a chance to recover. Millions of dollars have been spent gill-netting Lake Trout. Millions of fish have been taken.
Maybe this will make a difference. Succes is uncertain.
Known for sure is that we should not mess with Mother Nature.
