Tool-use frequency by individual sea otters in California

Sea otters are well-known tool users, employing objects such as rocks or shells to break open invertebrate prey. We used a series of generalized linear mixed effect models (GLMEs) to examine observational data on prey capture and tool use from 211 tagged individuals from five geographically defined study areas throughout the sea otters range in California. Our best supported model was able to explain 75% of the variation in the frequency of tool-use by individual sea otters with only ecological and demographic variables. In one study area, where sea otter food resources were abundant, all individuals had similar diets focusing on preferred prey items and used tools at low to moderate frequencies (4-38% of prey captures). In the remaining areas, where sea otters were food-limited, individuals specialized on different subsets of the available prey and had a wider range of average tool-use frequency (0-98% of prey captures). The prevalence of difficult-to-access prey in individual diets was a major predictor of tool use, and increased the likelihood of using tools on prey that were not difficult to access as well. Age, sex, and feeding habitat also contributed to the probability of tool use, but to a smaller extent. We developed a conceptual model illustrating how food abundance, the prevalence of difficult-to-access prey, and individual diet specialization interacted to determine the likelihood that individual sea otters would use tools and considered the models relevance to other tool-using species.

The dataset is an excel spreadsheet of tool-use frequency based on observed foraging behaviors of tagged sea otters in California. Foraging data was collected opportunistically on each individual over time (typically 1-3 years). For each successful foraging dive, observers recorded the type of habitat the sea otter was using, the prey type consumed, and whether a tool use used to open the prey item. These observations are summarized as the percent prey captures with tool-use observed for each grouping of prey type, habitat type, and individual sea otter. Dataset also includes the age, sex, and general location of each individual.

海獭是广为人知的工具使用物种，会借助石块、贝壳等物体破开无脊椎动物猎物。本研究采用一系列广义线性混合效应模型（Generalized Linear Mixed Effect Models, GLMEs），对加利福尼亚州海獭分布范围内5个地理研究区域内211只标记个体的猎物捕获与工具使用观测数据进行分析。最优拟合模型仅通过生态变量与种群统计变量，即可解释75%的个体海獭工具使用频率变异。在一处海獭食物资源充足的研究区域中，所有个体的食性均较为相似，以偏好猎物类群为主，工具使用频率处于中低水平（占猎物捕获事件的4%~38%）。在其余食物资源受限的研究区域中，海獭个体特化取食可获得猎物的不同子类群，平均工具使用频率的分布范围也更广（0%~98%的猎物捕获事件）。个体食谱中难获取猎物的占比是工具使用的核心预测因子，其不仅会提升个体对难获取猎物的工具使用概率，同时也会增加对非难获取猎物使用工具的可能性。年龄、性别与觅食生境也会对工具使用概率产生影响，但影响程度相对较弱。本研究构建了概念模型，用以阐释食物丰度、难获取猎物占比以及个体食性特化三者如何共同作用，决定海獭个体使用工具的概率，并探讨了该模型对其他工具使用物种的参考价值。
本数据集为Excel电子表格，记录了加利福尼亚州标记海獭觅食行为观测所得的工具使用频率数据。研究人员随时间对每只个体进行机会性觅食数据采集（通常为1~3年）。对于每一次成功的觅食潜水，观测人员会记录海獭所处的生境类型、取食的猎物种类，以及是否使用工具破开猎物。这些观测数据被汇总为：按猎物类型、生境类型与个体海獭分组后，各分组内使用工具完成的猎物捕获事件占比。数据集同时包含每只个体的年龄、性别与大致分布区域信息。