Data from: A preliminary range-wide distribution model for the Sacramento Valley red fox (Vulpes vulpes patwin)

The Sacramento Valley red fox (Vulpes vulpes patwin) of California (USA) is a newly named subspecies recently found to be distinct both from other native red foxes and nearby introduced populations. The Sacramento Valley red fox experienced a historical demographic bottleneck resulting in a critically small genetic effective population size, causing concern over its current status and management requirements, yet little is known about its contemporary abundance, demographic trajectory, or habitat use. The hot, arid Sacramento Valley contrasts starkly in climate and physiography with the boreal habitats of other indigenous red foxes in western North America, indicating the need to obtain information specifically on the habitat requirements of this subspecies. A 3-year effort to locate reproductive den sites throughout the Sacramento Valley resulted in 42 independent dens and 28 Sacramento Valley red foxes killed by vehicles (road kills), which we used to obtain preliminary information on habitat use and to develop a distribution model for this subspecies. Foxes were present significantly more than expected in grasslands and less than expected in wetlands and flooded agriculture and also tended to occur in proximity to human development, potentially as refuges from coyotes (Canis latrans). We used Maxent to build predictive models. The best model, which incorporated vegetation/land-use classes and proximity to human development, identified 24% of the study area as predicted-presence habitat, which contained 76% of the den sites used to construct the model and 89% of independent road kill locations used to test the model. Our model greatly narrowed the area over which foxes are predicted to occur and will facilitate future surveys to assess occupancy and ultimately abundance and population trends.

美国加利福尼亚州的萨克拉门托河谷赤狐（Vulpes vulpes patwin）是新近定名的亚种，研究证实其既区别于其他本土赤狐类群，也不同于邻近的引入种群。该亚种曾经历历史种群瓶颈，遗传有效种群规模极小，这引发了学界对其当前生存现状与管理需求的担忧，但目前对其当代种群数量、种群动态轨迹乃至栖息地利用情况的了解仍十分有限。炎热干旱的萨克拉门托河谷在气候与地形地貌上，与北美西部其他本土赤狐所栖息的北方生境形成鲜明对比，这表明亟需针对性获取该亚种的栖息地需求相关信息。我们历时3年在萨克拉门托河谷全境搜寻繁殖巢穴，共找到42处独立巢穴，以及28只因道路交通事故致死的萨克拉门托河谷赤狐（路杀个体），并以此为基础获取了该亚种栖息地利用的初步信息，同时构建了其分布预测模型。研究发现，赤狐在草地生境中的出现频率显著高于预期，而在湿地与淹水农田中的出现频率则低于预期；同时它们倾向于在人类开发区域附近活动，这可能是为了规避郊狼（Canis latrans）的捕食。我们采用最大熵模型（Maxent）构建预测模型，最优模型整合了植被/土地利用类型与距人类开发区域的距离两个变量，将研究区域的24%划定为预测适宜生境，该区域涵盖了建模所用76%的巢穴点位，以及用于模型验证的89%的路杀个体点位。本模型大幅缩小了该赤狐亚种的潜在分布范围，将为后续开展种群占用率评估，乃至最终的种群数量与种群趋势监测提供有力支撑。