BALD EAGLE, OSPREY, AND COMMON LOON SURVEYS
AT BULL RUN LAKE, 2006
Charlotte C. Corkran, Northwest Ecological Research Institute
NERI Report # 06-02
INTRODUCTION
As part of the 1998 Bull Run Lake Mitigation and Monitoring Implementation Plan (Plan), biannual monitoring of bald eagle (Haliaeetus leucocephalus) and osprey (Pandion haliaetus), and
annual monitoring of common loon (Gavia immer), are required. Ground-based surveys were
conducted during 2006.
The bald eagle is listed by the US Fish and Wildlife Service and the Oregon Department of Fish
and Wildlife as a Threatened Species. Both the common loon and osprey are considered potential
indicators of the presence of a prey base adequate to support bald eagles. Bald eagles are
occasionally seen at the Lake and elsewhere in the Bull Run Watershed, but there are no known
nest sites in the Watershed (Frank Isaacs, various reports and personal communication). Osprey
are known to nest annually in the Watershed, and at the Lake in many years (Corkran, Wetland
Wildlife Watch Annual Reports, 1987 to 2005). Loons occasionally are observed on the Lake
and are regularly observed in the Watershed. There is circumstantial evidence that loons may
have nested at the Lake in the late 1970s, but there has never been a loon nest confirmed in the
Watershed (Clyde Shaver, FS, pers. comm.; Rick Kneeland, FS, pers. comm.; Corkran,
unpublished reports, 1986 to 2003).
METHODS
As specified in the Plan, surveys were supposed to be conducted once every other week between
April 15 and July 1. However, I had to delay the schedule due to logistical difficulties and the
heavy and late snow pack in the mountains. The dates of the surveys were: April 28, May 14,
May 27, June 26, and July 3. Access to the Lake was by cross-country skis for the first visit.
None of the surveys was conducted by boat. On June 26, before visiting the lake, I tried viewing
it from a ridge just off the Pacific Crest Trail. Only one visit occurred between sunrise and five
hours after sunrise as specified in the Plan, and one visit occurred near sunset. The duration of
each observation period was between one and five hours, with most of the time spent scanning
from the porch of the cabin, and a portion of each survey was spent observing from the dike.
Binoculars (10 X) and spotting scope (20 X) were used from both positions.
RESULTS
No bald eagles, osprey, or loons nested at Bull Run Lake in 2006.
One observation of a bald eagle was made at the Lake. A sub-adult (probably 4 year old) was
seen perched on a snag on the island near the dike, but it was not seen on any other visits. Only
one other eagle sighting was made anywhere in the Watershed during the survey period, an adult
near Dam Number 1 on April 16.
Osprey was recorded only once at the Lake, on May 27 when a single bird was seen fishing and
then flying down the Bull Run River. The nest that remained from 2003, near Tributary 2 along
the northeast shoreline, never appeared to have been refurbished in 2006.
No sightings of common loon were made at the Lake during the survey period in 2006.
DISCUSSION
Osprey numbers in the Bull Run Watershed appeared to be about normal. I found 4 pairs active
at nests this year. Nest success was not fully monitored. Common loon activity was about
comparable to the last few years, with little or no pair activity on any of the reservoirs, but an
individual loon observed repeatedly in the same section of Reservoir #1 over several weeks.
There has been no evidence of loons nesting at the Lake or elsewhere in the Watershed since an
apparent failed nesting attempt at the upper end of Reservoir #1 in 1986.
Although observations of the three subject species were rare at Bull Run Lake during the 2006
surveys, a prey base appeared to be available for eagles. On one occasion, it appeared that an
osprey came to the Lake from elsewhere in order to forage, which could indicate that the Lake's
prey base was part of the territory of an osprey pair nesting in another location. On most visits, it
was possible to observe the dimples from fish foraging at the surface, not just around the
shoreline but throughout the northwest half of the Lake.
On the surveys conducted at midday and particularly the evening survey, it became apparent that
early morning may not be the best time of day for making eagle observations at the Lake. In
early morning, the observer is looking directly into the sun and at the shaded ridge slope to the
East. At midday, the light is good for observations in all directions, although eagles and other
birds may not be as active at that time. The late evening survey, besides yielding the only eagle
sighting this year, put strongly contrasting light directly on the slopes requiring scanning, and
made any bird or nest stand out in sharp relief. I recommend that future surveys include at least
two of the five visits in the evening. Maximum opportunity for observing bald eagles would be
gained by evening surveys combined with a continuation early the following morning (but that
would necessitate camping at the Lake).
ACKNOWLEDGMENTS
I thank Dave Corkran and Tara Pelletier for their assistance with some of the surveys, and Dave
for helping pioneer the Pacific Crest Trail eagle observation post.