Mass swarming of tens of thousands of common pipistrelles in front of hibernacula of the Carpathian Mountains suggests that bats may originate from a large catchment area. However, until now neither banding nor molecular data have resolved the geographic origin of common pipistrelles at these sites. Here, we measured the acoustic activity of bats and the stable hydrogen isotope ratios (δ2H) in metabolically inert fur keratin of bats to infer the relative swarming activity and the putative summer origin of bats, respectively, observed in autumn at Erňa cave, one of the largest bat hibernacula in Europe. Swarming activity declined with decreasing ambient temperature during the early season, while it increased during colder days towards the onset of hibernation. Based on δ2H values, we deduced that about 50% of the animals did not have a local origin. Provenance of all but one of these migrants was identified as the Pannonian Basin, while a single long-distance migrant may have originated from the northern margin of the species’ European distribution range. Modelling the variation in δ2H values of bats in response to sex, body condition and season suggested that, towards the onset of hibernation, males of low body condition were likely to be of distant geographic origin. Throughout the swarming season, females were mostly of local origin, yet towards the onset of hibernation, their body condition was not as variable as in males. We conclude that common pipistrelles observed at this mass hibernacula site are facultative migrants, which may undertake long-distance seasonal movements occasionally. At our study site, common pipistrelles are more likely to include long-distance migrants because of the mass occurrence of this species at this large hibernaculum.

中文翻译：

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追踪在大量冬眠中蜂拥而至的普通 pipistrelles (Pipistrellus pipistrellus) 的地理起源

喀尔巴阡山脉冬眠区前数以万计的普通 pipistrelles 的大量涌入表明蝙蝠可能来自一个大的集水区。然而，直到现在，条带和分子数据都没有解决这些地点常见 pipistrelles 的地理起源。在这里，我们测量了蝙蝠的声学活动和蝙蝠代谢惰性毛皮角蛋白中的稳定氢同位素比 (δ2H)，以分别推断蝙蝠的相对蜂群活动和假定的夏季起源，这是在秋季在 Erňa 洞穴观察到的欧洲最大的蝙蝠冬眠区。蜂群活动在早期随着环境温度的降低而下降，而在较冷的日子里随着冬眠的开始而增加。根据 δ2H 值，我们推断大约 50% 的动物没有本地来源。除了其中一个移民外，所有移民的出处都被确定为潘诺尼亚盆地，而单个长途移民可能起源于该物种欧洲分布范围的北缘。对蝙蝠 δ2H 值随性别、身体状况和季节的变化进行建模表明，在冬眠开始时，身体状况不佳的雄性可能来自遥远的地理起源。在整个蜂拥季节，雌性大多是本地人，但在冬眠开始时，它们的身体状况不像雄性那样多变。我们得出结论，在这个大规模冬眠地点观察到的常见 pipistrelles 是兼性迁徙者，它们偶尔会进行长距离的季节性运动。在我们的研究现场，