Print PageRegular return migrations are known from seasonal environments but rather uncommon in tropical equatorial habitats where opportunistic movements prevail. Here we show here that Galapagos tortoises on Santa Cruz Island anticipate, and make use of, the seasonal temperature and food flush in the Galapagos archipelago by conducting altitudinal return migrations. As an ectotherm, Galapagos tortoise behavior is directly linked to ambient temperature and we investigate how temperature influences movement in over multiple temporal scales. We begin by using latent-state movement models that allow us to integrate relocation and accelerometer data to describe behavior over the course of the day. We then discuss how broader trends in temperature are correlated with the timing of upward and downward migration. Lastly we explore seasonal size and sex based biases in the population distribution along an altitudinal gradient.
Results/Conclusions
Using accelerometer and relocation data we are able to distinguish activity and relate it to temperature. Over the course of a day, Tortoises regulate their behavior to avoid exposure to temperature extremes. The timing of activity differs between individuals in the two populations because of the prevailing aspect in these two portions of the Island. We also show that the movements of individuals and the timing of population redistribution are linked to cooling and warming. The beginning of seasonal warming is associated with upward migration and the beginning of cooling is associated with downward migration. Using population surveys we also detail sex and size biases in the population distribution along an altitudinal gradient. Tortoises live for decades to centuries, however as juveniles they are more sensitive to temperature fluctuations, have lower reserves and move less efficiently. As a consequence, they are less likely to undergo altitudinal migration and are restricted to lower altitudes throughout the year.
