1. We present a novel application using unoccupied aircraft systems (UAS; drones) for structure-from-motion three-dimensional (3-D) photogrammetry of multiple, free-living animals simultaneously. Pinnipeds reliably haul out on shore for pupping and breeding each year, accompanied by dramatic female-to-pup mass transfer over a short lactation period and males lose mass while defending mating territories. This provides a tractable study system for validating the use of UAS as a non-invasive tool for tracking energy dynamics in wild populations.
2. UAS imagery of grey seals Halichoerus grypus was collected at Saddle Island, Nova Scotia. A multirotor UAS was piloted in 360-degree orbits around relatively dense animal aggregations and georeferenced images were used for construction of a 3-D point cloud, orthomosaic and Digital Surface Model for animal volumetric measurements. Directly following UAS survey, a subset of adult females were hand-measured (morphometrics, blubber depth, n = 21 handlings [15 were unique animals]) and female–pup pairs were weighed (adult females: n = 32 [24]; pups: n = 33 [23]) to validate that UAS 3-D photogrammetric models provided accurate animal volume and mass estimates.
3. UAS two-dimensional body length measurements were sensitive to animal recumbency and posture. The new UAS 3-D photogrammetric method overcame these constraints, and aerial-derived body volume measurements were equivalent to those collected from the ground. UAS body volume measurements precisely predicted ‘true’ body mass (mean absolute error, adult female: 3.8 kg, 2.1% body mass; pup: 4.1 kg, 9.8%), and exhibited a stronger relationship with total body mass than with blubber volume.
4. The method was applied to 673 free-living animals to characterize volume and mass dynamics across lactation and breeding for a much larger sample size than would be possible using traditional ground methods. Indeed, 1–46 animals (M ± SE: 9.2 ± 1.2) were modelled concurrently within the focal area of a UAS flight. Application of the method also captured significant inter-annual variation in body volume/mass dynamics, and female-to-pup energy transfer efficiencies were lower when there was low sea ice extent. The UAS 3-D photogrammetric method presented in this study is likely to be broadly applicable to other species, and the ability to measure whole groups of free-living animals at once makes strides towards ‘weighing populations’.

中文翻译：

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使用无人飞机系统和三维摄影测量跟踪野生动物能量动态

1. 我们提出了一种使用无人飞机系统（UAS；无人机）同时对多个自由生活动物进行结构-运动三维 (3-D) 摄影测量的新应用。鳍足类动物每年都会可靠地上岸进行幼崽和繁殖，伴随着在较短的哺乳期期间雌性与幼崽之间的戏剧性质量转移，雄性在保卫交配领地时会失去质量。这提供了一个易于处理的研究系统，用于验证 UAS 作为跟踪野生种群能量动态的非侵入性工具的使用。
2. 在新斯科舍省的马鞍岛收集了灰海豹Halichoerus grypus 的UAS 图像。多旋翼无人机在 360 度轨道上围绕相对密集的动物群进行飞行，地理参考图像用于构建用于动物体积测量的 3D 点云、正射镶嵌和数字表面模型。紧接着 UAS 调查，对一部分成年雌性进行了手工测量（形态测量学、鲸脂深度、n  = 21 次处理 [15 是独特的动物]）并称重雌性-幼崽对（成年雌性：n  = 32 [24]；幼崽） : n  = 33 [23]) 以验证 UAS 3-D 摄影测量模型提供了准确的动物体积和质量估计。
3. UAS 二维体长测量对动物的卧姿和姿势很敏感。新的 UAS 3-D 摄影测量方法克服了这些限制，空气衍生的人体体积测量值与从地面收集的测量值等效。UAS 体重测量精确地预测了“真实”体重（平均绝对误差，成年女性：3.8 公斤，2.1% 体重；幼犬：4.1 公斤，9.8%），并且与总体质量的关系比与脂肪体积的关系更强。
4. 该方法应用于 673 只自由生活的动物，以表征哺乳期和繁殖期间的体积和质量动态，样本量比使用传统地面方法可能的样本量大得多。实际上，在 UAS 飞行的焦点区域内同时模拟了1-46 只动物（M  ±  SE：9.2 ± 1.2）。该方法的应用还捕获了身体体积/质量动力学的显着年际变化，并且当海冰范围较低时，雌性到幼犬的能量转移效率较低。本研究中提出的 UAS 3-D 摄影测量方法可能广泛适用于其他物种，并且一次测量整个自由生活动物群体的能力向“称重种群”迈进了一大步。