Dens are important for species that need to survive and reproduce during harsh winters. Brown bears (Ursus arctos) in Romania, listed by the European Union as a population of concern, use dens for several months each year. To date, few quantitative assessments of denning habitat have been carried out for this population or others in Europe. In 2008–2013 and 2015–2017, we used local knowledge and telemetry data from brown bears fitted with GPS collars to identify 115 winter dens and eight open ground nests used by bears in eastern Transylvania, Romania. We located most dens in mountainous areas (64%) and fewer in foothills (36%). Den entrances in mountainous areas were significantly narrower than entrances in foothills, likely due to the need for reduced thermal loss during more severe winters at higher elevations. We selected seven habitat characteristics (abiotic and biotic) and human-related covariates associated with known locations of dens and open nests to identify potential brown bear denning habitat using maximum entropy modeling. We found that terrain ruggedness was the single most important factor when predicting bear denning habitat. The habitat map derived from this study can be used in the future to safeguard bear denning areas from potential human disturbances.

中文翻译：

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罗马尼亚东部特兰西瓦尼亚棕熊巢穴特征与选择

巢穴对于需要在严冬中生存和繁殖的物种很重要。罗马尼亚的棕熊 (Ursus arctos) 被欧盟列为受关注种群，每年都有几个月的时间使用巢穴。迄今为止，几乎没有对欧洲的这一种群或其他种群进行过栖息地的定量评估。在 2008-2013 年和 2015-2017 年，我们利用当地知识和来自装有 GPS 项圈的棕熊的遥测数据，确定了罗马尼亚特兰西瓦尼亚东部的熊使用的 115 个冬季巢穴和 8 个露天巢穴。我们的大多数窝点位于山区 (64%)，而在山麓 (36%) 的窝点较少。山区的巢穴入口明显比山麓的入口窄，这可能是因为需要在海拔较高的更严冬期间减少热量损失。我们选择了七个栖息地特征（非生物和生物）以及与已知的巢穴和开放巢穴位置相关的人类相关协变量，以使用最大熵模型确定潜在的棕熊栖息地。我们发现，在预测熊窝栖息地时，地形崎岖是最重要的一个因素。从这项研究中得出的栖息地地图可以在未来用于保护熊栖息地免受潜在的人类干扰。