Pronghorn Migration Corridors - Bodie-Wassuk - 2014-2016 [ds3100]

The project leads for the collection of this data were Tim Taylor and Tom Stephenson. Pronghorn (20 adult females) were captured and equipped with GPS collars (Televilt Tellus Iridium, Sweden) transmitting data from 2014-2016. The Bodie-Wassuk herd contains migrants, but this herd does not migrate between traditional summer and winter seasonal ranges. Instead, much of the herd displays a somewhat nomadic migratory tendency, moving between the Bodie Hills east of U.S. Highway 395 in California to a basin west of the Wassuk Range between Aurora Crater and Corey Peak in Nevada. A few collared individuals moved as far north as the Gray Hills, staying west of the Wassuk Range, with one individual moving as far south as the Alkali Valley. Therefore, annual ranges were modeled using year-round data to demarcate high use areas in lieu of modeling the specific winter ranges commonly seen in other ungulate analyses in California. GPS locations were fixed at 4-hour intervals in the 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 pronghorn 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 the herd’s annual range and the identification and prioritization of migration corridors. Brownian Bridge Movement Models (BBMMs; Sawyer et al. 2009) were constructed with GPS collar data from 18 migrating pronghorn, including 102 migration sequences, location, date, time, and average location error as inputs in Migration Mapper. The average migration time and average migration distance for pronghorn was 4.85 days and 17.44 km, respectively. 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 rate of 1000. Annual range analyses were based on data from 17 pronghorn and 21 year-round sequences using a fixed motion variance of 1000. Annual range designations for this herd may expand with a larger sample, filling in some of the gaps between annual range polygons in the map. Corridors are visualized based on pronghorn use per cell, with less than or equal to1 pronghorn and less than or equal to 4 pronghorn (20 percent 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 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. Annual range is visualized as the 50th percentile contour of the annual range utilization distribution.