Raptors (Birds of Prey)
More than a dozen raptor species can be seen in Yellowstone. Three-peregrine falcons, bald eagles, osprey-are carefully monitored. The peregrine falcon and eagle were formerly on the federal list of endangered and threatened species. Their monitoring is required by law. The fish-eating osprey is being monitored because it is especially vulnerable as cutthroat trout decline in Yellowstone Lake.
Monitored since the 1980s, when the bald eagle was placed on the federal list of threatened species, Yellowstone's population of bald eagles is relatively stable. In 2007, it was removed from the federal threatened species list, and monitoring continues. Each year, 40 to 60 percent of nests succeed (produce eggs), with each nesting pair producing an average of 0.71 eaglets (average from 1987-2012). These statistics are slightly lower than expected for a stable and healthy population, and may be explained by the park's harsh environment, especially during the early breeding season (February-April).
Finding Bald Eagles in Yellowstone
In 1962, Rachel L. Carson sounded an alarm about the irresponsible use of pesticides with her landmark book, Silent Spring. Among the dangers she described were the adverse effects of chemicals-particularly DDT-on the reproductive capacity of some birds, especially predatory species such as the bald eagle and peregrine flacon. Her book raised public awareness of this issue, and was one of the catalysts leading to the United States banning the most damaging pesticides.
The peregrine falcon was among the birds most affected by the toxins. It was listed on the endangered species list. Yellowstone National Park was a site for peregrine reintroduction in the 1980s, which were discontinued when the peregrine population began increasing on its own. The falcon made a comeback in much of its former range, and was delisted in 1999. For 15 years after the delisting, the peregrine will be monitored closely, and scientists will watch for threats to their population.
Yellowstone's relatively pristine conditions and long-term monitoring of peregrines provides baseline information to compare against other U.S. populations. Continued monitoring is essential, not only for comparisons with other populations, but also because peregrine falcons and other raptors are reliable indicators of contaminants (such as PBDE-polybrominated diphenyl ether) and climate change. For example, to assess the levels of PBDE, scientists collect eggshell remains after peregrines have left their nests for the season.
Like many other birds of prey, osprey populations declined due to pesticides in the mid-20th century. Its populations rebounded during the latter part of the 20th century. Monitored since the late 1980s, Yellowstone's population of osprey is considered relatively stable. On average, 50 percent of nests succeed (produce eggs) each year, with each nesting pair producing an average of 0.82 young (average from 1987-2012. These statistics are slightly lower than expected for a stable and healthy population, and may be explained by the park's harsh environment. The number of Ospreys nesting at Yellowstone Lake has declined since 2001 and those few pairs that continue to nest at the lake are generally unsuccessful. A recent study revealed that declines in cutthroat trout as a result of introduced lake trout are primarily responsible.
Did You Know?
There are more people hurt by bison than by bears each year in Yellowstone. Park regulations state that visitors must stay at least 25 yards away from bison or elk and 100 yards away from bears.