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The project leads for the collection of this data were Julie Garcia and Evan King. Mule deer (32 adult females) from the Kern River herd were captured and equipped with Lotek LiteTrack Iridium collars, transmitting data from 2020-2022. GPS fixes were set for 2-hour intervals. The Kern River herd migrates from winter ranges in Sequoia National Forest north of Johnsondale and east of Slate Mountain northward to the area around Redrocks Meadows and along the Kern Canyon ridgeline to Sequoia National Park. Due to a high percentage of poor fixes, likely due to highly variable topographic terrain, between 2-18% of GPS locations per deer, or 5.78% of the entire dataset, were fixed in 2-dimensional space and removed to ensure locational accuracy.
The methodology used for this migration analysis allowed for the mapping of winter ranges and the identification of migration corridors and stopovers. Brownian Bridge Movement Models (BBMMs; Sawyer et al. 2009) were constructed with GPS collar data from 27 migrating deer, including 75 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 15.76 days and 31.51 km, respectively. Corridors and stopovers were prioritized based on the number of animals moving through a particular area. Separate models using Brownian bridge movement models (BMMM) and fixed motion variances (FMV) of 1000 were produced per migration sequence. Due to high variances, Only FMV models were retained. Corridors 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 28 individual deer and 59 wintering sequences using a fixed motion variance of 1000. 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. Additional migration routes and winter range areas likely exist beyond what was modeled in our output.
Corridors are visualized based on deer use per cell in the BBMMs, with greater than or equal to 1 deer, greater than or equal to3 deer (10% of the sample), and greater than or equal to 6 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 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.