This project was initiated by the CDFW Central Region and was conducted on a portion of the Tuolumne herd that migrate to the Jawbone Ridge flats in the winter in Tuolumne County, Mariposa County, and Alpine County. Jawbone Ridge and the adjacent winter range habitat was further divided into the Clavey and Cherry sub-herd units. Additionally, a small sample of deer were captured from the Yosemite herd (south of the Tuolumne herd) to determine herd overlap. The raw dataset consisted of GPS way points collected from Advanced Telemetry Solutions (ATS) store on board GPS collars (G2110B/D model) and were placed on female mule deer only. Individuals were captured via darting or clover traps. This data was collected from 2009-2015 by Nathan Graveline and Ronald Anderson. GPS collars were set to take a location every 7 hours, and emit a signal Monday through Friday, 9am to 5pm. Some GPS collars were set to take a location fix every hour during periods of time when deer were thought to be migrating (May and November). The Clavey and Cherry sub-herd units support the highest concentration of wintering deer within the Tuolumne deer herd range. The majority of deer in these two sub-herds migrate east into the Emigrant and Yosemite Wilderness, with a few heading north to the Carson-Iceberg Wilderness. Low density populations of non-migratory deer are present in the winter range. Forest practices, wildfires, and recreation (hunting, camping, OHV) represent the most significant impacts to this herd. To improve the quality of the data set as per Bjørneraas et al. (2010), theGPS 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 from 83 deer, including location, date, time, and average location error as inputs in Migration Mapper. 245 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. Due to varying fix rates, separate models using Brownian bridge movement models (BMMM) and fixed motion variances of 1000 were produced per migration sequence and visually compared for the entire dataset, with best models being combined prior to population-level analyses (25% of sequences selected with BMMM). Migration corridors, stopovers, and winter range analyses were produced separately for the Yosemite Herd sample (n = 6) and merged with the Tuolumne dataset given the smaller capture effort and intention to prioritize moderate and high use corridors specifically in the Tuolumne herd. Winter range analyses were based on data from 85 individual deer in total. A separate BBMM was created for all deer locations designated as winter range using a fixed motion variance parameter of 1000. Winter range designations for this herd would likely expand with a larger sample south of Jawbone Ridge (Yosemite Herd) due to a small capture sample size from this area, 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 in the BBMMs, with greater than or equal to 1 deer, greater than or equal to 9 deer (10% of the sample), and greater than or equal to 17 deer (20% of the sample) 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 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.