Nature Notes From Crater Lake
Volume 24, 1993
Spotted Owl Survey
By Lori Stonum
The northern spotted owl (Strix
occidentalis caurina) is one of three subspecies of spotted owls. It
is a medium-sized forest owl distinguished by its large brown eyes and
mottled brown and white breast. The spotted owl is a monogamous,
long-lived species, that is mostly nocturnal. Ranging from southern
British Columbia to northern California, it is found on the east and
west slopes of the Cascade Range and on the Olympic Peninsula. Spotted
owls live mostly in low elevation coniferous old growth forests and have
a limited seasonal migration.
The first recorded observation of a
spotted owl at Crater Lake National Park was in 1934. Between 1934 and
1978, there were several other sightings reported. The first surveys of
the spotted owl at the park were conducted in 1978 in cooperation with
the Oregon Department of Fish and Wildlife and the U.S. Forest Service.
Sporadic studies have been conducted since then, but a complete census
was never conducted. Until 1986, studies within the park concentrated on
the west side of the Cascade Range. When the surveying resumed in 1990,
the southern portion of the park was included. The 1990 and 1991
surveys, however, consisted only of two-day projects with limited
coverage of the park's spotted owl habitat.
A more comprehensive survey of the
northern spotted owl at Crater Lake National Park commenced in May 1992.
This was the first year that a study of spotted owls in the park was
conducted according to standard protocol. Survey sites were determined
based on historic spotted owl sites, areas of good habitat, and the
location of proposed construction within the park. Since the survey was
started late in the season compared to others in the region, we
concentrated on historic owl sites and future construction zones, making
them our priority. New sites were added as time became available.
Overall, the number of owls found at
Crater Lake in 1992 was unexpected. We now know that the park holds
greater significance for spotted owls than previously thought. During
the 1990 and 1991 surveys, two pairs and one single male spotted owl
were found each year. By the end of the 1992 field season, we had
located seven pairs of spotted owls. Six of the seven pairs had two
juveniles. Three single owls of unknown reproductive status were also
found, making a total of 29 owls found in the park. Of these, 12 owls
were banded with the help of the Oregon Department of Fish and Wildlife
so that the owls can be identified in future studies.
The 1992 spotted owl survey produced
two significant findings. One was the large number of owls located on
the east side of the Cascade Range. Four pairs of spotted owls found in
the park this year were on the east side of the Cascades, which was
somewhat unexpected when considering that most spotted owls are found
west of the mountains. The second finding was the relatively high
elevation at which several owl pairs were living. For two years in a
row, Crater Lake National Park has held the state record for the highest
elevation at which a spotted owl pair was found. The Annie Creek site
was the 1991 state record at 1829 meters (6000 ft.), and in 1992 it was
the Crater Peak site at 1996 meters (6550 feet). In future studies we
hope to be able to focus on these east side and high elevation sites to
determine if there are factors influencing the owl's range and
reproductive status, as compared to west side and lower elevation sites.
There is still a lot of work to be done
in the park on spotted owls. Less than 30 percent of the 50,000 acres of
spotted owl habitat existing within Crater Lake National Park was
surveyed. Considering the exciting results of the 1992 survey, the
potential for even greater numbers of owls existing within the park is
very high. If the spotted owl program at Crater Lake can continue to
expand and survey more of the suitable habitat, perhaps the complete
status of the spotted owls at Crater Lake could be better known.
