Usefulness and limitation of a tiny light-temperature logger to monitor daily activity levels of arboreal squirrels in temperate areas

Abstract

Owing to recent advances in technology, biologging has revealed in-depth animal behavior at a level of detail that previously could not be obtained. However, previous studies were limited to relatively large species due to constraints caused by the size of data loggers. Some recent studies, however, applied tiny light loggers (geolocator) to monitor daily activity levels of small rodents in the southern arctic and far north Holarctic. In this study, we tested whether a similar method can be applied to arboreal squirrels in temperate regions, by combining light intensity and temperature data. Inside the squirrel’s nest was dark enough during daylight hours to capture out of nest activity with light intensity, clearly showing daily and seasonal changes in diel activity patterns. The new temperature function on the device showed consistently high temperature within the nests (35–37 °C) and suggested additional activity before sunrise; the squirrels were primarily diurnal, but occasionally left their nest for short periods (an average of 13 min) during the night. We also found that estimates of daily activity time changed depending on the threshold cut-off values of light intensity and provide a recommendation of 5 to 25 lx for future studies. In addition, temperature loggers were not always effective during summer when warmer ambient temperature approached the squirrel’s body temperature. While the inexpensive and tiny light-temperature logger has potential to monitor activity levels of small mammals, care should be taken when analyzing the output.