The project leads for the collection of these data were Shelly Blair (CDFW) and Jerrod Merrell (University of Nevada Reno). Mule deer (52 adult females) from the Pacific herd were captured and equipped with store-onboard GPS collars (Vectronic Plus Vertex Survey Iridium), transmitting data from 2015-2020. Pacific mule deer are found on the western slope of the Sierra Nevada in eastern California and exhibit largely traditional seasonal migration strategies. This population migrates from a multitude of lower elevation areas in the foothills of El Dorado National Forest in winter westward into higher elevation summer ranges. Migrants vary in their movements from shorter (6 km) to longer (41 km) distances.

GPS locations were fixed between 1-13 hour intervals in the dataset. To improve the quality of the dataset, the GPS data were filtered prior to analysis to remove locations which were 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 43 migrating deer, including 149 migration sequences, location, date, time, and average location error as inputs in Migration Mapper. The average migration time and average migration distance for deer was 7.79 days and 26.72 km, respectively. Corridors and stopovers were prioritized based on the number of animals moving through a particular area. Corridors and stopovers were best visualized using a fixed motion variance of 500 per sequence. Winter range was processed with a fixed motion variance of 1000. All products were produced at a spatial resolution of 50 m using a sequential fix interval of less than 27 hours. Winter range analyses were based on data from 32 individual deer and 54 wintering sequences. 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.

Corridors are visualized based on deer use per cell, with greater than or equal to 1 deer, greater than or equal to 5 deer (10 percent of the sample), and greater than or equal to 9 deer (20 percent of the sample) representing migration corridors, moderate use 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 m2 were 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 50th percentile contour of the winter range utilization distribution.