Living on the edge - circadian habitat usage in pre-weaning European hares (Lepus europaeus) in an intensively used agricultural area

Over the last decades, the European hare (Lepus europaeus) has become the subject of many interdisciplinary studies due to the sharp Europe-wide population decline. In European hares, the first stage of life until weaning and the subsequent dispersal have been sparsely studied, in particular, habitat selection, movements and survival rate, as juveniles´ precocial lifestyle is dominated by concealment, motionlessness and inconspicuousness. In this study, free-living juvenile European hares (leverets) were detected systematically by thermography (n = 394), radio-tagged or marked (n = 122) from birth until the fifth week of life to research their habitat usage and pre-dispersal movements. The day-resting places and night locations, as well as the distance moved by leverets with aging, were evaluated by generalized linear mixed effect models. In addition, the habitat preference was assessed by a conservative use-availability analysis. Up to the fifth week of life, 30.5% of all leverets used cultivated areas in the daytime. In contrast, the remaining 69.4% animals inhabitated linear or small planar structures in the daytime, with the edges of field tracks, hedges and some ruderal structures clearly being preferred. At nighttime, 93% of all juveniles, which occupied linear structures in the daytime, used the adjoining fields up to 20 m away from the next linear structure. Nocturnal distances of more than 60 m to the next edge rarely occurred before the end of the pre-weaning phase. The time of day and age have a significant influence on the distance moved by juvenile hares. With increasing age, leverets moved less during the day and roamed further at night. The results are largely consistent with the behavioral patterns found in the few previous studies on pre-weaning European hares and show the importance of hiding places for leverets in early life stages. This study should contribute to a better understanding of behavior in juvenile life-history stages of European hares that may help to identify vulnerable phases in their lifecycle. In addition, the findings can refine existing population models and improve conservation efforts.近数十年来，因欧洲全境欧洲野兔（Lepus europaeus）种群数量急剧下降，该物种已成为诸多跨学科研究的核心研究对象。现有针对欧洲野兔的研究中，关于其断奶前生命初始阶段以及后续扩散过程的内容仍较为匮乏，尤其是幼崽的生境选择、活动移动与存活率——这是由于幼崽的早成性生活模式以隐蔽、静止与低可见性为主要特征。本研究通过热成像（thermography）系统探测到野生幼年欧洲野兔（幼野兔，leverets）共394只，其中122只被施以无线电标记或个体标识，跟踪周期覆盖其出生至出生后第五周，以探究其生境利用规律与扩散前的移动模式。研究人员采用广义线性混合效应模型（generalized linear mixed effect models）分析了幼野兔的日间休憩位点、夜间活动位置，以及随日龄增长的移动距离；此外还通过保守型利用-可用性分析（use-availability analysis）评估了其生境偏好。截至出生后第五周，共有30.5%的幼野兔会在日间利用耕作农田生境。与之相对，剩余69.4%的个体日间会选择线性或小型面状生境，其中田埂边缘、树篱与部分荒生植被结构（ruderal structures）为其显著偏好的休憩位点。夜间时段中，日间选择线性生境的幼野兔中有93%会利用紧邻该线性结构、距离不超过20米的周边农田生境。在断奶前阶段结束前，幼野兔夜间移动距离超过60米至相邻生境边缘的情况极少出现。日龄与日间时段对幼野兔的移动距离存在显著影响。随着日龄增长，幼野兔日间的移动量逐渐减少，而夜间的活动范围则逐步扩大。本研究结果与既往针对断奶前欧洲野兔的少量研究中观察到的行为模式大体一致，同时证实了早期生命阶段中隐蔽位点对幼野兔的重要性。本研究有助于更深入地理解欧洲野兔幼年期的生命史行为模式，或可帮助识别其生命周期中的脆弱阶段；此外，本研究的发现还可优化现有种群模型，助力野生动物保护工作的改进。