CWMP 2017-2018 Winter Report
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Methodology
Study Area
Snoqualmie Pass (3022 feet, 921 meters) is the lowest pass in the Washington Cascades.
Interstate 90 traverses the pass from west to east as a divided highway with two to four
lanes of traffic in each direction throughout the study area. A large downhill ski complex
sits at the summit of the pass, along with associated human infrastructure. A few miles east
of the pass, a large irrigation water reservoir on the headwaters of the Yakima River fills
much of the valley bottom. The human footprint at the pass along with the high speed and
heavily trafficked interstate highway makes Snoqualmie Pass the most tenuous wildlife
corridor in the Washington Cascades. Ongoing reconstruction by the Washington
Department of Transportation on Interstate 90 east of Snoqualmie Pass has been designed
to improve road safety for motorists and increase the permeability of the road for wildlife.
Field Methods
CWMP employs trained volunteers to walk transects adjacent to the interstate and
document the tracks of wildlife. Set transects are monitored three times over the course of
the winter on average and were established at locations where crossing structures either
exist and are being improved or have been targeted for installation. Transects run parallel
to the highway about 150 meters from the roadbed. Field teams document tracks and signs
of any mammal species larger than a snowshoe hare found along the route. At least one set
of tracks is trailed on each transect per visit in an attempt to document the animal's
relationship to the interstate. Observations are photo-documented in the field and all
photos are reviewed by expert observers out of the field to assess observer reliability. All
species of high conservation value are thoroughly documented, including photo-
documentation, to ensure the accuracy of identification.
American marten surveys are not along prescribed routes. Rather, general locations are
assigned to a field team to survey. These survey areas are based on an attempt to fill in a
more complete picture of landscapes currently occupied and unoccupied by the species
adjacent to the highway corridor. This information will hopefully help identify the closed
points of linkage for northern and southern populations and obstacles to connectivity for
them. A route is selected based on access considerations and how to best cover the area.
Teams record a GPS track of the route they take so that the project can track locations that
have been surveyed and the amount of effort. Teams record tracks of American marten
when they are detected as per the project protocol for on-transect surveys.
Results
Summary of 2018 Transect Data
During the winter field season 62 species detections were made across all 10 transects, 41
detections (66 %) were identified to species (8 species total, Figure 1) and the remaining
21 were ambiguous. Across detections, 33 were travelling parallel to roadway, 7 away from
the roadway, and 14 towards the roadway. The remaining 7 had an unknown relationship
to the roadway. Only a single level-one species was detected, a cougar at Price Noble. Two
