eNut: A Sensing System to Measure the Acquisition of Foraging Proficiency in Wild Tree Squirrels

We present a three-part sensing system to measure the acquisition of foraging proficiency in wild tree squirrels. The first component is the eNut: a 3-D printed enclosure in the size and shape of a large food item, such as a walnut. The eNut contains an inertial measurement unit (IMU), consisting of an accelerometer and a gyroscope, along with a capsule containing a food reward (e.g., chopped nuts), motivating the squirrel to manipulate the eNut to open the reward capsule. The second component is a radio frequency identification (RFID) gate that can detect the presence of a known individual. The reader generates time-stamped labels for the analysis of simultaneous video recordings of the squirrel movements. Finally, the third component is a data collection pipeline, which aggregates the sensor data in a cloud backend server. The design process culminated in a fully functional prototype system tested under three field conditions: two outdoor sites used for juvenile squirrel rehabilitation and a third site with free-ranging adult squirrels. The accuracy of the collected data is assessed by leveraging laboratory settings in which acceleration and rotation were checked against reference values produced by a testing infrastructure, custom-built for this application. Finally, we present an inventory of food item manipulation movements (rotation and shaking) that are identified and quantified with the eNut system. This system allows a level of granular analyses of foraging decisions that was not feasible with prior technology, which would have important translational value in paradigms of animal behavior and wildlife rehabilitation.