Lemming monitoring on Bylot Island, Nunavut, Canada

Lemming abundance and demography are monitored using three methods: Capture by snap trapping is done using Museum Special traps at three sites during the summer from mid-July to early August since 1994. At least 500 trap-nights are cumulated annually at each site. From 1994 to 2006, there were 50 trapping stations with one trap per station and trapping sessions lasted for 10 or 11 consecutive days. Trapping stations were spaced out every 10 m along two or more parallel trapping lines separated by 100 m (Gruyer et al. 2008). The sampling protocol changed from 2007 onward. There are now 80 trapping stations (except in 2007 and 2008 when there were only 68 stations) with three traps per station and trapping sessions last for 3 or 4 consecutive days. Each trapping stations are spaced out every 15 m along two or more parallel trapping lines which are separated by 100 m (Fauteux et al. 2018). All captured animals are identified at the species level. Capture-mark-recapture by live trapping animals is conducted using Longworth traps on three grids, one of 7 ha (96 to 100 traps depending of the year) and two of 11 ha (144 traps; from 2004 to 2005, only 7 ha and 100 traps)), in wetland (one grid) and mesic (two grids) habitats since 2004. Traps are positioned in a Cartesian plane and spaced out every 30 m. Traps are checked every 12 hrs during trapping sessions that last three consecutive days (4 or 5 days in 2004 to 2007) and which are repeated three times (four times in 2005 to 2007) during the summer from mid-June to mid-August. Since 2015, three grids of 7 ha (96 to 100 traps/grid) were added in mixed habitat (wetland and mesic). Those three grids are monitored for only one trapping session in mi-July. The species, age (juvenile or adult, based on body mass), sex and reproductive condition of captured animals is determined (for more details, see Gruyer et al. 2010, Bilodeau et al. 2013 and Fauteux et al. 2018). One of the live-trapping grids in mesic habitat (the one of 7 ha) was subjected to various experimental manipulations. From 2007 to 2011, snow fences were used to enhance snow depth to determine its effect on lemming abundance and distribution. Snow fences (1.3 m high) were erected in six rows of fencing 270 m-long each and perpendicular to the prevailing wind (spacing varied between 30 and 50 m). Since 2013, this grid is used for a predator control experiment. All terrestrial and avian predators (except ermine) are excluded by a 1.3 to 2-m high fence made of chicken wire surrounding the grid and covered by criss-crossing fishing line spaced every 50 cm on top. Lemming winter nests are surveyed after snow-melt in early July using the line transect method since 2007. Each transect is permanent (since 2009), is 500 m long and is randomly located within each habitat. A total of 60 line transects were surveyed in wetlands, mesic tundra and streams in mesic tundra (20 transects/habitat) between 2009 and 2014. In 2007 and 2008, the number of transects were 75 (25 per habitat) and 30 (10 per habitat), respectively. Between 2015 and 2017, 66 line transects were added to increase the spatial coverage of the monitoring for a total of 126 permanent line transects (between 5 and 20 transects/habitat/sector). Between 2015 and 2019, several line transects were added to increase the spatial coverage of the monitoring for a total of 139 permanent line transects (between 6 and 20 transects/habitat/sector). The exact position of each nest found along the transect is recorded. In addition, each spring, all winter nests are systematically counted on three live trapping grids by walking parallel lines 10 m apart. Winter nests found opportunistically are also collected in years of low lemming abundance. All nests are dissected to determine the lemming species using it, reproductive activity and signs of predation (for more details, see Duchesne et al. 2011a, b and Fauteux et al. 2018).

自1994年起，通过三种方法对鼠兔种群丰富度和种群学特征进行监测：采用博物馆专用捕捉器进行捕捉，自7月中旬至8月初在三个地点进行，每年每个地点累积至少500个捕捉夜。1994年至2006年间，设有50个捕捉站点，每个站点一个捕捉器，捕捉周期为10或11个连续日。捕捉站点沿两条或多条相距100米的平行捕捉线均匀分布，间距为10米（Gruyer等，2008年）。自2007年起，采样方案有所变更。目前有80个捕捉站点（2007年和2008年除外，当时仅有68个站点），每个站点配备三个捕捉器，捕捉周期为3或4个连续日。每个捕捉站点沿两条或多条相距100米的平行捕捉线均匀分布，间距为15米（Fauteux等，2018年）。所有捕获的动物均按物种进行鉴定。

通过现场捕捉动物进行捕捉-标记-重捕，采用Longworth捕捉器在三个网格上进行，其中一个是7公顷（每年96至100个捕捉器），另外两个是11公顷（2004年至2005年，仅7公顷和100个捕捉器），自2004年起在湿地（一个网格）和温带生境（两个网格）中进行。捕捉器在笛卡尔平面上定位，间距为30米。捕捉周期为连续三天（2004年至2007年为4或5天），每年夏季从6月中旬至6月中旬重复三次（2005年至2007年为四次）。自2015年起，在混合生境（湿地和温带）中增加了三个7公顷的网格（每个网格96至100个捕捉器），仅在7月中旬进行一次捕捉。捕获动物的物种、年龄（幼年或成年，根据体重）、性别和繁殖状况得到确定（更多细节，见Gruyer等，2010年，Bilodeau等，2013年，Fauteux等，2018年）。

在温带生境中的一个7公顷的现场捕捉网格进行了各种实验处理。从2007年到2011年，使用雪篱来增加雪的深度，以确定其对鼠兔种群丰富度和分布的影响。雪篱（高1.3米）被安装在六排270米长的围栏中，与盛行风向垂直（间距在30至50米之间）。自2013年起，该网格用于捕食者控制实验。通过一个由鸡丝网制成、高1.3至2米、顶部覆盖交叉鱼线的围栏将所有陆地和鸟类捕食者（除貂之外）排除在外。自2007年以来，利用线样法对鼠兔冬季巢穴进行调查，每个样线均为永久性（自2009年起），长度为500米，在每种生境内随机定位。2009年至2014年间，在湿地的湿地、温带苔原和温带苔原的溪流中调查了60条样线（每个生境20条样线）。2007年和2008年，样线数量分别为75条（每个生境25条）和30条（每个生境10条）。2015年至2017年，增加了66条样线，以增加监测的空间覆盖范围，总数达到126条永久样线（每个生境/区域5至20条样线）。2015年至2019年间，又增加了几条样线，以增加监测的空间覆盖范围，总数达到139条永久样线（每个生境/区域6至20条样线）。沿样线找到的每个巢穴的确切位置都得到记录。此外，每年春天，通过沿10米间隔的平行线行走，对三个现场捕捉网格上的所有冬季巢穴进行系统计数。在鼠兔种群丰富度低的年份，也会收集偶然发现的冬季巢穴。所有巢穴都被解剖，以确定使用的鼠兔物种、繁殖活动和捕食迹象（更多细节，见Duchesne等，2011a，b，Fauteux等，2018年）。