The project leads for the collection of this data were Sara Holm with California Department of Fish and Wildlife and Mike Cox with Nevada Department of Wildlife. Carl Lackey and Cody Schroeder of the Nevada Department of Wildlife and Julie Garcia of California Department of Fish and Wildlife also contributed to the completion of the mapping and project. The Verdi-Truckee mule deer herd primarily winters south of Interstate 80 in the Carson Range along the California-Nevada border, although a portion of this herd also winters north and east of Verdi, Nevada on Peavine Mountain. Migration routes to summer range follow I-80 southwest along both sides of the Truckee River toward Martis Valley and Truckee, California. The summer range for this small herd (approximately 500 animals estimated in 2019) is located east the town of Truckee, California and includes portions of Juniper Flat, Martis Creek, and south of the Truckee River to the confluence of Gray Creek. Migration behavior and timing of migration is highly dependent on seasonal weather conditions and the depth of snow during late fall and early winter periods. Significant challenges to this deer herd include barriers to movement, such as Interstate 80 and associated vehicle collisions, as well as increased housing development on winter range in the Garson Road area and surrounding Verdi neighborhoods. Twenty-five adult female mule deer were captured and fitted with store-on-board GPS collars from 2009 to 2010, and additional deer were collared sporadically between 2012-2017. Between 2 and 22 location fixes were recorded per day. 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 deer 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 in a single deer population. Brownian Bridge Movement Models (BBMMs; Sawyer et al. 2009) were constructed with GPS collar data, including location, date, time, and average location error as inputs in Migration Mapper. Thirty-one deer contributing 91 migration sequences were used in the modeling analysis. 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. Winter range analyses were based on data from 31 individual deer and 74 wintering sequences using a fixed motion variance of 1000. 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 deer use per cell, with greater than or equal to 1 deer, greater than or equal to 3 deer (10% of the sample), and greater than or equal to 6 deer (20% of the sample) from the Loyalton dataset representing migration corridors, moderate use, 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.