June 10, 2010
A Tale of Two Yellowstone Birds
Peregrine falcons and trumpeter swans are two of the most important and charismatic birds in Yellowstone National Park. Both are also species of national concern, as they have each faced extinction during the last century. Habitat in Yellowstone plays a key role in maintaining viable populations of both peregrines and trumpeters, yet one of these bird species is now flourishing while the other is floundering. Now researchers are trying to figure out why.
Peregrine Falcons: An Astonishing Recovery
By the 1960s, peregrine falcons had been wiped out in Yellowstone due to the use of organochlorine pesticides, such as DDT, and by 1970 were considered in danger of extinction. However, since the United States banned the chemicals in 1972, peregrines have made an astonishing recovery from the brink of extinction and have returned to Yellowstone. Peregrines were delisted in 1999, but remain a Species of Concern and are closely monitored in the Park.
With a wingspan of about 40 inches, the peregrine falcon is among the world’s fastest birds, flying at 40– 55 mph and diving at more than 200 mph when striking avian prey in mid-air.
In addition to their impressive physical feats, as mid-level avian predators, peregrines have an important ecological function in the Park’s food chain. As migrants, they also serve as “sentinels” for identifying exterior environmental contamination affecting the Greater Yellowstone ecosystem.
Trumpeter Swans: A Grave Situation
Trumpeter swans, a species unique to North America, were nearly exterminated due to unrestricted killing for feather harvesting. By 1935, the only trumpeter swans thought to exist in the lower 48 states were 69 birds living year-round in the Greater Yellowstone Ecosystem. Conservation efforts during the late 20th century saved the species from extinction. Throughout this time, the small flock persisted in Yellowstone and reached an all-time high of 100 swans in 1992.
Despite population increases in recent years -- a continent-wide survey in 2005 found 34,803 birds -- trumpeters are still designated a Species of Concern, and have been declining rapidly in Yellowstone. Reproduction is low and cygnet mortality is high. In 2009, there were no cygnets produced in the Park.
While more than a hundred trumpeters that migrate from Canada spend the winter in Yellowstone, the known resident population is now down to six birds. The prospect of future extinction of Yellowstone’s resident population is highly likely if current trends continue.
Causes of the decline are not entirely known, but it is assumed that the Yellowstone population is affected by the environment, as well as feeding and management practices at a nearby wildlife refuge, and possibly predation. Drought conditions over the last decade are believed to affect the wetlands used for nesting.
The trumpeter swan, so named for its resonant, trumpet-like call, was known to exist in Yellowstone when the Park was established in 1872. It is North America’s largest wild waterfowl. Facing a future without Yellowstone’s stately and beloved swans, the National Park Service is prioritizing research on why trumpeters are dwindling in such an alarming way.
Peregrine Falcon & Trumpeter Swan Monitoring Project
The Yellowstone Park Foundation is supporting a three-year research project to monitor the Park’s populations of these two birds. The goals are to determine what environmental and other factors affect these species, and generate recommendations on how they should be conserved in the future.
Peregrines are the most sought after species for recreational falconers and illegal taking of chicks does occur. Knowledge of all eyries (nests) in the Park will aid Yellowstone law enforcement in protecting this iconic bird. It will also give Park managers a better understanding of the distribution of peregrines and the full extent of recovery. There are currently at least 32 known eyries in Yellowstone.
Park biologists, joined by one outside researcher, will locate peregrine falcon eyries in the Park, monitor eyrie occupancy, determine nest success, and document any environmental contaminants from tissue samples or egg shells. The egg shells are significant because the earlier decline in the population was caused by a pollutant -- DDT -- which thinned the egg shells. Locating potential nest sites is time consuming and labor intensive, as likely sites are high cliffs, with open air space below, near water.
In the case of the trumpeter swan, the researchers are conducting an inventory of habitat conditions and gathering information on possible causes of the population decline. Aerial photographs are being used to locate and map the Park for wetlands, and wetlands will be assessed and compared using historic photographs. Swan nests will be plotted using GIS software and analyzed against wetland change.
The funds for the Peregrine Falcon & Trumpeter Swan Monitoring Project are supporting the allocation of staff so that surveys -- both ground and aerial – can occur to help locate and track both bird populations. Additional expenses include sampling equipment and supplies. No bird capture is planned for this study.
Ultimately, the knowledge gained from concentrated research and monitoring will enable Park biologists and managers to work toward maintaining healthy populations of peregrine falcons and trumpeter swans in Yellowstone.
Watch a 2-minute video on trumpeter swans>>
Read more about peregrine falcons>>
Learn some interesting facts about trumpeter swans>>