Bear in mind! Bear presence and individual experience with calf survival shape the selection of calving sites in a long-lived solitary ungulate

Female moose were immobilized with a CO2-powered dart gun (DANiNJECT, Kolding, Denmark) from a helicopter with a mixture of etorphine-acepromazine-xylazine or etorphine-xylazine (Evans et al., 2012; Græsli et al., 2020; Kreeger & Arnemo, 2007; Lian et al., 2014). Each female was equipped with a neck collar with a global positioning system (GPS) device, including a very high frequency (VHF) transmitter, a global system for mobile (GSM) communication, an ambient temperature recorder, and an acceleration sensor to monitor their movement over time (Vectronic Aerospace GmbH, Berlin, Germany, 2022). Using the GSM network or satellite, the tracking device sends continuous positions to the existing database Wireless Remote Animal Monitoring (WRAM; Dettki et al., 2014), which allows us to monitor females remotely in near real-time. The GPS provided half-hourly locations of the moose females, which we resampled for the habitat selection analysis to four times a day (00.00h, 06.00h, 12.00h, and 18.00h). Since moose are mostly active during dusk and dawn and females with calves move small distances during this period of the year (Neumann et al., 2012), we deemed four samples a day sufficient to capture female positions during both resting and active times to describe their major habitat selection. Moose are long-lived, mostly solitary-living, capital breeders with a life span of more than 20 years (Ericsson & Wallin, 2001). Females usually calve every year but their fertility decreases after the age of 15 years (Niedzialkowska et al., 2022). In our study, female age averaged 8.3 years (range 4-16 years) at their time of capture as indicated by their tooth wear (Ericsson & Wallin, 2001). All personnel handling the moose were certified according to the standards of the Swedish Animal Welfare Agency and the Swedish Board of Agriculture. The marking of moose has been approved by the Animal Care Committee in Umeå, Sweden (DNR A116-09, A12-12, A50-12, A205-12, A14-15, A3-16, A28-17, A11-2020). For each female, we linked movement data to her age and reproductive success in a given year (i.e. calf survival, calf loss due to predation or an unknown cause), resulting in a dataset including the calving date, the number of calves born, their summer survival, and the movement and age of the female. To study the effect of the female experience on her selection for habitat structures at the calving site during the first four weeks following parturition in a given year, we built step selection functions using five random steps for each observed step. We extracted habitat features at the end of the step to test for the selection of a given habitat feature (R package ‘amt’, Signer et al., 2019). To test for site fidelity of female moose in relation to the bear presence and females’ experience over the years, we modeled the observed inter-annual distances between calving site locations in successive years calculated as Euclidean distances (km) separately for each female. For each female, we calculated this distance as the distance between the daily average GPS collar locations in successive years, for each day, starting from the birth date (day 0) through the end of the first week after calving (day 7). This allowed us to compare female selection (i.e. derived by the coordinates) both at the date of calving and during the first week among successive years.

研究人员借助直升机，使用二氧化碳驱动的飞镖枪（DANiNJECT，丹麦科灵市）为雌性驼鹿实施麻醉，麻醉方案采用埃托啡-乙酰丙嗪-赛拉嗪混合剂或埃托啡-赛拉嗪混合剂（Evans et al., 2012; Græsli et al., 2020; Kreeger & Arnemo, 2007; Lian et al., 2014）。每头雌性驼鹿均佩戴集成有全球定位系统（Global Positioning System, GPS）设备的颈圈，该设备包含甚高频（Very High Frequency, VHF）发射器、全球移动通信系统（Global System for Mobile Communications, GSM）通信模块、环境温度记录仪与加速度传感器，用于长期监测其活动轨迹（德国柏林Vectronic Aerospace GmbH，2022）。追踪设备可通过GSM网络或卫星将实时位置数据传输至已有的无线远程动物监测（Wireless Remote Animal Monitoring, WRAM; Dettki et al., 2014）数据库，实现对雌性驼鹿的近实时远程监测。GPS设备每半小时记录一次雌性驼鹿的位置数据，我们将其重采样为每日4次（00:00、06:00、12:00及18:00），用于后续栖息地选择分析。鉴于驼鹿多在黄昏与黎明时段活跃，且带幼崽的雌性驼鹿在该年度时段活动范围相对有限（Neumann et al., 2012），我们认为每日4次采样足以覆盖雌性驼鹿休息与活动的核心时段，从而准确刻画其主要栖息地选择行为。驼鹿为长寿、独居型资本繁育者，自然寿命可达20年以上（Ericsson & Wallin, 2001）。雌性驼鹿通常每年产崽，但15岁后生育能力会出现显著下降（Niedzialkowska et al., 2022）。本研究中，通过牙齿磨损情况判定，雌性驼鹿被捕获时的平均年龄为8.3岁（年龄范围4~16岁）（Ericsson & Wallin, 2001）。所有接触驼鹿的实验人员均已通过瑞典动物福利署与瑞典农业委员会的资质认证，该驼鹿佩戴项圈的实验方案已获得瑞典于默奥大学动物护理委员会批准（DNR A116-09、A12-12、A50-12、A205-12、A14-15、A3-16、A28-17、A11-2020）。我们将每头雌性驼鹿的活动数据与其年龄以及特定年份的繁殖成功率（即幼崽存活率、因捕食或未知原因导致的幼崽死亡数）进行关联，最终构建得到包含产崽日期、产崽数量、幼崽夏季存活率以及雌性驼鹿活动轨迹与年龄信息的数据集。为探究雌性驼鹿的繁殖经验对其在特定年份产崽后前四周内选择产崽地栖息地结构的影响，我们针对每一条观测到的移动步长，生成5条随机步长以构建步长选择函数，并提取步长终点的栖息地特征，以此检验其对特定栖息地特征的选择偏好（R包‘amt’，Signer et al., 2019）。为检验雌性驼鹿的巢址保真度与熊类存在情况以及多年间繁殖经验的关联，我们针对每头雌性驼鹿，分别计算其连续年份间产崽地位置的欧氏距离（千米），以此作为年度间移动距离。具体计算方式为：以产崽当日（第0天）至产崽后第一周结束（第7天）的每日平均GPS项圈位置为基准，计算连续年份间的上述距离。该方法可用于比较不同年份间雌性驼鹿在产崽当日及产崽后第一周的栖息地选择（即通过坐标推导得出）情况。