Elk Home Range - Cortina Ridge - 2017-2022 [ds3030]

The project leads for the collection of this data were Josh Bush and Tom Batter. Elk (7 adult females, 8 adult males) from the Cortina Ridge herd were captured and equipped with Lotek GPS collars (LifeCycle 800 GlobalStar, Lotek Wireless, Newmarket, Ontario, Canada), transmitting data from 2017-2022. The study area was within the Bear Valley Elk Management Unit, east of Route 20 and southeast of Mendocino National Forest. Route 20 appears to be a barrier to movement, as these elk do not overlap with the Bear Creek Ranch – Antelope Valley herd on the other side of the road. The Cortina Ridge herd contains short distance, elevation-based movements likely due to seasonal habitat conditions, but this herd does not migrate between traditional summer and winter seasonal ranges. Instead, the herd displays a residential pattern, slowly moving up or down elevational gradients. 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 at 13-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 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 analysis allowed for the mapping of the herd’s annual range based on a small sample. Brownian Bridge Movement Models (BBMMs; Sawyer et al. 2009) were constructed with GPS collar data from 12 elk in total, including 31 year-long sequences, location, date, time, and average location error as inputs in Migration Mapper to assess annual range. Annual range BBMMs were produced at a spatial resolution of 50 m using a sequential fix interval of less than 27 hours. Population-level annual range designations for this herd may expand with a larger sample, filling in some of the gaps between high-use annual range polygons in the map. Annual range is visualized as the 50th percentile contour (high use) and the 99th percentile contour of the year-round utilization distribution.本数据集的采集项目负责人为乔希·布什（Josh Bush）与汤姆·巴特（Tom Batter）。研究对象为科蒂纳岭鹿群（Cortina Ridge herd）的15头麋鹿：7头成年雌性、8头成年雄性。研究人员对其实施捕捉并佩戴Lotek GPS项圈（LifeCycle 800 GlobalStar，加拿大安大略省纽马克特市Lotek无线公司生产），数据采集时段为2017年至2022年。本研究区域位于贝尔谷麋鹿管理区（Bear Valley Elk Management Unit），地处20号公路以东、门多西诺国家森林（Mendocino National Forest）东南侧。观测表明20号公路构成了麋鹿移动的屏障，该鹿群与公路另一侧的溪溪牧场——羚羊谷鹿群（Bear Creek Ranch – Antelope Valley herd）不存在活动区域重叠。科蒂纳岭鹿群存在基于海拔的短距离移动，该现象大概率与季节生境条件相关，但该鹿群并未在传统的夏季与冬季活动范围间进行迁徙。相反，该鹿群呈现定居模式，仅缓慢沿海拔梯度上下移动。因此，研究采用全年采集的数据对年度活动范围进行建模，以划定高频使用区域，而非效仿加州其他有蹄类动物分析的常规做法，单独针对冬季活动范围开展建模。本数据集的GPS定位间隔为13小时。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，研究人员在正式分析前对GPS数据进行了滤波处理，移除以下三类定位点：i） 与前一个或后一个定位点的距离超出单头麋鹿在对应时段内可移动的最大距离；ii） 基于进出速度与转弯角度判定的运动轨迹尖峰，且转弯角度较预设阈值更为锐利；iii） 采用二维定位且经分析师目视判定为无效的定位点。本分析采用的方法可基于小样本量绘制该鹿群的年度活动范围。研究借助迁移映射器（Migration Mapper），以共计12头麋鹿的GPS项圈数据为输入项（包含31组全年序列、定位坐标、日期、时间与平均定位误差），构建了布朗桥运动模型（Brownian Bridge Movement Models，BBMMs），以此评估年度活动范围。模型空间分辨率设置为50米，采用的连续定位间隔小于27小时。若后续样本量扩大，该鹿群的种群级年度活动范围划定范围可能会进一步扩展，填补地图中高频使用年度活动范围多边形间的部分空白。本研究将年度活动范围可视化呈现为全年利用分布的50%分位数轮廓（高频使用区域）与99%分位数轮廓。