Elk Home Range - Sherwood - 2022-2023 [ds3086]

The project lead for the collection of this data was Carrington Hilson. Elk (2 adult females) were captured and equipped with GPS collars (Lotek Iridium) transmitting data from 2022-2023. The Sherwood herd does not migrate between traditional summer and winter seasonal ranges. Therefore, annual home 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 between 1-7 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 home range. Brownian bridge movement models (BBMMs; Sawyer et al. 2009) were constructed with GPS collar data from 2 elk, including 2 annual home range sequences, location, date, time, and average location error as inputs in Migration Mapper. BBMMs were produced at a spatial resolution of 50 m using a sequential fix interval of less then 27 hours. Home range is visualized as the 50th percentile contour (high use) and the 99th percentile contour of the year-round utilization distribution. Home range designations for this herd may expand with a larger sample.本数据集的项目负责人为卡林顿·希尔森（Carrington Hilson）。研究团队捕获2头成年雌性马鹿（Elk），并为其佩戴Lotek铱星GPS项圈（Lotek Iridium），该设备于2022至2023年间持续传输定位数据。谢伍德种群（Sherwood herd）不会在传统的夏、冬季活动范围之间进行迁徙，因此本研究未效仿加州其他有蹄类动物分析中常见的做法单独建模冬季活动范围，而是采用全年定位数据对年度家域（home range）进行建模，以划定该种群的高频使用区域。本数据集中的GPS定位点采用1至7小时的固定间隔进行采集。为提升数据集质量，参照比约纳拉斯等人（Bjørneraas et al., 2010）的研究方法，分析前对GPS数据实施滤波处理，以移除以下三类不合格定位点：其一，与前一定位点或后一定位点的距离超出叉角羚（pronghorn）在该间隔时间内的可行移动范围；其二，基于出射速度、入射速度及大于预设阈值的转弯角度，在运动轨迹中形成尖峰的点位；其三，仅采用二维定位且经分析人员目视判定为无效的定位点。本次迁徙分析所采用的方法可实现该种群家域的可视化制图。研究以2头马鹿的GPS项圈数据为输入参数，在Migration Mapper软件中构建布朗桥运动模型（Brownian bridge movement models, BBMMs；Sawyer et al., 2009），输入内容包含2组年度家域序列、定位坐标、日期、时间及平均定位误差。该模型以50米的空间分辨率、小于27小时的连续定位间隔生成。家域通过全年利用分布（utilization distribution）的50%分位数等高线（高频使用区）与99%分位数等高线进行可视化呈现。该种群的家域范围可能随着后续样本量的扩大而进一步拓展。