The project leads for the collection of this data were Erin Zulliger and Richard Shinn. The winter range of the West Goose Lake Rocky Mountain elk (Cervus canadensis nelsoni) sub-herd is located north of Alturas and west of Highway 395 within the Devil’s Garden Ranger District of the Modoc National Forest. This area is characterized by juniper (Juniperus occidentalis) woodlands, and sagebrush flats with some stands of lodgepole (Pinus contorta) and ponderosa pine (Pinus ponderosa) throughout flat, rocky terrain. From this area, a portion of the herd migrates approximately 50 miles north into Oregon’s Fremont National Forest, habitat that primarily consists of lodgepole and ponderosa pine forests. Minimal barriers exist along this migration route since the corridor primarily occurs on land managed by the US Forest Service. Additionally, although the core migration route does cross Highway 140, little to no impacts are known to exist from this crossing. Elk (12 adult females, 1 adult male, and 3 juvenile [less than 1 year of age] males) were captured from 2018 to February 2020 and equipped with Lotek and Vectronic satellite GPS collars. Additional GPS data was collected from elk (2 females and 1 male) in 1999-2002 and included in the analysis to supplement the small sample size of the 2018-2020 dataset. GPS locations were fixed at 4-hour intervals in the 2018-2020 dataset and 6 to 8-hour intervals in the 1999-2002 dataset. To improve the quality of the data set as per Bjørneraas et al. (2010), the GPS data were filtered prior to analysis to remove locations which were: i) further from either the previous point or subsequent point than an individual elk is able to travel in the elapsed time, ii) forming spikes in the movement trajectory based on outgoing and incoming speeds and turning angles sharper than a predefined threshold , or iii) fixed in 2D space and visually assessed as a bad fix by the analyst.

The methodology used for this migration analysis allowed for the mapping of winter ranges and the identification and prioritization of migration corridors. Brownian Bridge Movement Models (BBMMs; Sawyer et al. 2009) were constructed with GPS collar data from 12 migrating elk, including 25 migration sequences, location, date, time, and average location error as inputs in Migration Mapper. Five migration sequences from 3 elk, with an average migration time of 6.8 days and an average migration distance of 16.14 km, were used from the 1999-2002 dataset. All three of these elk were used to supplement the eastern members of this herd, which travel shorter distances between summer and winter range than western individuals in the sample. Twenty migration sequences from 9 elk, with an average migration time of 11.2 days and an average migration distance of 57.75 km, were used from the 2018-2020 dataset. Corridors and stopovers were prioritized based on the number of animals moving through a particular area. BBMMs were produced at a spatial resolution of 50 m using a sequential fix interval of less than 27 hours and a fixed motion variance of 1400. Winter range analyses were based on data from 11 individual elk and 18 wintering sequences using a fixed motion variance of 1400. Winter range designations for this herd would likely expand with a larger sample, filling in some of the gaps between winter range polygons in the map. Large water bodies were clipped from the final outputs.

Corridors are visualized based on elk use per cell, with greater than or equal to 1 elk and greater than or equal to 3 elk (20% of the sample) representing migration corridors and high use corridors, respectively. Stopovers were calculated as the top 10 percent of the population level utilization distribution during migrations and can be interpreted as high use areas. Stopover polygon areas less than 20,000 m2were removed, but remaining small stopovers may be interpreted as short-term resting sites, likely based on a small concentration of points from an individual animal. Winter range is visualized as the 50thpercentile contour of the winter range utilization distribution.