The project leads for the collection of this data were Erin Zulliger and Richard Shinn. Elk (6 adult females, 3 juvenile [less than 1 year of age] males, and 2 juvenile females) were captured in 2017 and equipped with Lotek satellite GPS collars or VHF tags, transmitting data from 2017-2020. Additional GPS data was collected from elk (6 females) in 2001-2002 and included in the analysis to supplement the small sample size of the 2017-2020 dataset. The Egg Lake elk herd migrates from a winter range surrounding Egg Lake in Modoc County, California eastward into Siskiyou County for the summer. GPS locations were fixed at 4-hour intervals in the 2017-2020 dataset and 3 to 8-hour intervals in the 2001-2002 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 11 migrating elk, including 22 migration sequences, location, date, time, and average location error as inputs in Migration Mapper. Nine migration sequences from 5 elk, with an average migration time of 6.78 days and an average migration distance of 26.83 km, were used from the 2000-2001 dataset. Fourteen migration sequences from 6 elk, with an average migration time of 7.79 days and an average migration distance of 42.40 km, were used from the 2017-2020 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 22 wintering sequences using a fixed motion variance of 1400. Winter range designations for this herd may 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.