Nature Notes

Volume XXIV - 1993

sketch of peregrine falcon
Falco peregrinus

Peregrine Falcons Soar Over Crater Lake
By Scott Stonum

Peregrine Falcons (Falco peregrinus) are crow-sized falcons that are distributed throughout the world. Their diet consists of other birds. Chemicals such as Dichloro Diphenyl Trichloroethane (DDT) tend to accumulate in their system because the peregrine is at the top of the food chain. DDT, which was banned in the United States in 1972, has caused thinning of egg shells and dehydration. The chemical continues to be a problem because the pesticide is still being used in Mexico and South America, where many peregrines or their food sources migrate.

The only known active peregrine eyrie in Oregon in recent years was at Crater Lake National Park. It was discovered in 1979, and remained active until 1983, when both adult birds disappeared. Although the birds in the eyrie successfully fledged young in 1979, they were unsuccessful in 1980. Each of the three eggs laid the second year showed high levels of a derivative of DDT. As a result, young peregrines were fostered into the nest in 1981 and 1982.

When both adult peregrines disappeared in 1983, a method of releasing birds into the wild known as hacking was initiated. Twelve young were hacked over the next four years. Roaming peregrines were seen at the hack site in all four years, and non-breeding peregrines were seen in other areas around Crater Lake. An active pair was present at the historic eyrie in 1986, but successful breeding did not take place.

Nesting again took place at Crater Lake in 1987. The nest was manipulated to ensure that the pair would successfully fledge young. Four eggs were removed from the nest, three of which hatched and were fledged in California. Two captive-bred young were fostered into the Crater Lake eyrie. Unfortunately, one of the young was killed by a great horned owl (Bubo virginianus Gmelin). The other bird successfully fledged.

The peregrines again used the historic eyrie in 1988. They laid four eggs, of which three hatched. Approximately twelve days later all of the young and the adult female were killed by a great horned owl. In order to ensure fledging of peregrines in the Crater Lake area it was decided to cross-foster young peregrines into a nearby prairie falcon nest. This effort was successful in fledging two peregrines that year.

It is believed that the male returned with an immature female in 1989 and 1990, but monitoring during those years was limited. In 1991 the historic eyrie was again active. An adult peregrine pair was successful in fledging three young without any manipulation. Of interest was the male of the pair being identified as a released bird due to the band on its leg. The spring and summer of 1992 was also a successful breeding season for the falcons. Two eggs were produced in the eyrie with both young subsequently being fledged.

The successful fledging of young peregrines during the past two years is very promising and is the result of much effort and patience. The site will again be monitored during 1993. Should the falcons continue to nest at the same eyrie, steps may need to be taken to monitor great horned owls in the area and to evaluate the effects of predation on the peregrines. Although the hatching success in recent years has been good, analysis of the eggs shows significant thinning and that the female was subjected to pesticide contamination.

Air Quality at Crater Lake
By Heidi Lyn Ross and David Lee Fuller

Most people visiting Crater Lake find themselves in awe of the beautiful blue water. When they gasp at the beauty, they should also realize that they are breathing some of the cleanest air in the world.

The air is so pure at Crater Lake that on the clearest day you can see at least 190 miles, and occasionally to the 240 mile limit. Actual day to day visibility at Crater Lake averages about 105 miles.

There are some threats, however, to Crater Lake's air quality. Klamath Falls and Medford, each about 55 air miles from Crater Lake, are non-attainment areas in the state; this means that these cities do not comply with Oregon's goals for air quality in populated areas. Nevertheless, the small amount of pollution we do have is not directly associated with an urban or industrial corridor. Weather patterns in those areas usually trap the pollutants to the ground. At Crater Lake, air movement is generally characterized by westerly winds associated with the presence of weather systems formed over the Pacific Ocean. Air pollution over the park is usually particulate from slash burning, wildfires, and agricultural burning.

One big reason efforts are being made to protect our air is that preserving scenic vistas is a boon to tourism. Although fire danger is a compelling reason to prohibit slash burning during the summer months, land managers want to keep visibility at its best during the tourist season. Oregon hosts 11.8 million visitors every year who spend over $1.4 billion in the state. Roughly $17.4 million of that total is spent to visit the state's wilderness areas, including Crater Lake National Park.

The National Park Service and the Oregon Department of Environmental Quality monitor the air at Crater Lake in four different ways:

Standard Visual Range (SVR) data is collected by a 35mm camera which photographs a vista of known distance three times a day. Calculations are made of how far past, or in front of a known target the horizon can be seen in the photograph. Estimates of how many particles are in the air are made by calculating how well the target contrasts with the area in front of it and behind it. There are three SVR cameras in the park. One is located on Dutton Cliff and another is on Watchman; both are aimed at Yamsay Mountain to the east of the park. A third camera is at Rim Village, where it can view Mount Theilson to the north of Crater Lake.

The Transmissometer has a transmitting station at Rim Village that sends a light beam across the lake to a receiving station at Wineglass on the northeast side of the lake. By calculating how much light is sent and how much is received, the amount lost traveling from one site to another can be determined. The light is scattered by particles in the air, so the more light received, the cleaner the air.

The Nephelometer is an instrument that takes air into a vacuum tube and sends light through the sample. It then measures the intensity of light that is scattered by particles contained within the instrument's optical path. The less the light is scattered the cleaner the air. The park's Nephelometer is located at Rim Village.

Finally, the Improve pulls air through many different filters. Each filter is a different degree or size, meaning each filter will catch a different sized particle. To see what particles are in the air, each filter is chemically analyzed. This device is located at Park Headquarters.

Through use of this technology and other indicators, we know that the air quality over Crater Lake has been impacted by human activities. Presently, naked eye visibility at Crater Lake National Park is substantially impaired for 4.6 percent of all daylight hours. Nevertheless, this figure is impressive when compared with stations further north in Oregon. Crater Lake is, in fact, often the standard used when judging air quality in other areas. By contrast, Mount Hood's visibility is impaired 21 percent of the time, while Mount Washington's figure is 42 percent and Portland's is 85 percent.

Although a 4.6 percent impairment index may seem satisfactory when compared to other areas, this may rise to five, ten, or even 20 percent without the cooperation of people. We all have a responsibility to ensure clean air--our next breath depends on it.

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