Animal perception of seasonal thresholds: changes in elephant movement in relation to rainfall patterns

Background: The identification of temporal thresholds or shifts in animal movement informs ecologists of changes in an animal’s behaviour, which contributes to an understanding of species’ responses in different environments.In African savannas, rainfall, temperature and primary productivity influence the movements of large herbivoresand drive changes at different scales. Here, we developed a novel approach to define seasonal shifts in movementbehaviour by examining the movements of a highly mobile herbivore (elephant; Loxodonta africana), in relation tolocal and regional rainfall patterns.Methodology/Principal Findings: We used speed to determine movement changes of between 8 and 14 GPS-collaredelephant cows, grouped into five spatial clusters, in Kruger National Park, South Africa. To detect broad-scalepatterns of movement, we ran a three-year daily time-series model for each individual (2007–2009). Piecewiseregression models provided the best fit for elephant movement, which exhibited a segmented, waveform patternover time. Major breakpoints in speed occurred at the end of the dry and wet seasons of each year. During thedry season, female elephant are constrained by limited forage and thus the distances they cover are shorter andless variable. Despite the inter-annual variability of rainfall, speed breakpoints were strongly correlated withboth local and regional rainfall breakpoints across all three years. Thus, at a multi-year scale, rainfallpatterns significantly affect the movements of elephant. The variability of both speed and rainfall breakpointsacross different years highlights the need for an objective definition of seasonal boundaries.Conclusions/Significance: By using objective criteria to determine behavioural shifts, we identified abiologically meaningful indicator of major changes in animal behaviour in different years. We recommend the use of such criteria, from an animal’s perspective, for delineating seasons or other extrinsic shifts in ecological studies, rather than arbitrarily fixed definitions based on convention or common practice.