Elk Migration Corridors - East Shasta Valley - 1999-2001, 2016-2020 [ds2903]

The project leads for the collection of this data were Erin Nigon and Michael Hunnicutt. The East Shasta Valley sub-herd of Rocky Mountain elk (Cervus canadensis nelsoni) range as far east as the eastern foothills of Shasta Valley, as far north as the Klamath River, and as far south and east as Deer Mountain. In the winter, these elk spend most of their time on private ranchlands in Shasta Valley. This area offers patches of oak woodlands and grasslands on gentle slopes. In the spring, elk migrate to their summer range around Grass Lake, Bull Meadows, and Deer Mountain where the habitat is primarily characterized by mixed conifer timber stands of Ponderosa pine (Pinus ponderosa), lodgepole pine (Pinus contorta) and Douglas fir (Pseudotsuga menziesii). The meadows around Grass Lake seem especially important to this sub-herd, as neonatal calves have been documented in this area since at least 1984 (Fischer 1987). Some animals from this sub-herd have moved into Oregon periodically, while others have moved long distances eastward to other sub-herds, but Highway 97 presents a significant barrier to this movement. Most elk mortality due to vehicle collisions on Highway 97 has been documented to occur between Horsethief Creek, and Grass Lake Summit (California Department of Transportation, unpublished data). Because of this, a wildlife crossing is proposed for this area to promote habitat connectivity and wildlife movement. Elk (5 adult females, 5 juvenile [less than 1 year of age] males, and 8 juvenile females) were captured from 2016 to 2020 and equipped with Lotek satellite GPS collars. Additional GPS data was collected from elk (7 females and 1 male) in 1999-2001 and included in the analysis to supplement the small sample size of the 2016-2020 dataset. GPS locations were fixed at 4-hour intervals in the 2016-2020 dataset and 3 to 8-hour intervals in the 1999-2001 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 elk 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 18 migrating elk, including 59 migration sequences. GPS location, date, time, and average location error were used as inputs in Migration Mapper. Fifty-one migration sequences from 10 elk, with an average migration time of 4.87 days and an average migration distance of 22.14 km, were used from the 2016-2020 dataset. Fourteen migration sequences from 8 elk, with an average migration time of 7.43 days and an average migration distance of 30.08 km, were used from the 1999-2001 dataset. Average migration distance and time were higher in 1999-2001 dataset due to a single male elk outlier; removing this outlier led to a mean migration distance of 20.36 km and a mean migration time of 5.75 days for the 1999-2001 dataset. 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 of 1400. Winter range analyses were based on data from 15 individual elk and 28 wintering sequences using a fixed motion variance of 1400. Large water bodies were clipped from the final outputs. Corridors are visualized based on elk use per cell, with greater than or equal to 1 elk and greater than or equal to 4 elk (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 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.