Pronghorn Migration Corridors - Lassen - 2014-2016 [ds2933]

The project leads for the collection of this data were Brian Ehler and Kristin Denryter. Pronghorn (7 adult females) were captured and equipped with GPS collars (Sirtrack, Havelock North, NZ) transmitting data from 2014-2016. The Lassen herd winters in lower elevations in the Secret Valley, Bull Flat, and Mud Flat north of the Skedaddle Mountains and east of Shaffer Mountain, as well as in the Dry Valley Rim Wilderness Study Area. Summer ranges are spread out, with some individuals migrating north to the Five Springs Wilderness Study Area and others heading east to Tunnison Mountain Wilderness Study Area and Eagle Lake. GPS locations were fixed between 1-6 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 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 7 migrating pronghorn, including 14 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 18.43 days and 36.30 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 12 hours. Due to varying fix rates in the data, separate models using Brownian bridge movement models (BMMM), with an adaptable variance rate, 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 (78% of sequences selected with BBMM). Winter range analyses were based on data from 6 individual deer and 9 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. Large water bodies were clipped from the final outputs. Corridors are visualized based on pronghorn use per cell, with greater than or equal to 1 deer and greater than or equal to 2 pronghorn (20% 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. Winter range is visualized as the 50th percentile contour of the winter range utilization distribution.