Tracking toads from dusk till dawn: Linking inter- and intra-individual variation in movement behavior

Abstract

Animals can differ in their individual movement behaviors during their daily displacements. Studies of animal movement patterns often disregard the need to understand individual variation in these patterns and the role of this variation in shaping population distributions of movements. To assess the link between individual movements and population distributions, we radio tracked 13 Fowler’s Toads (Anaxyrus fowleri) in Long Point, Ontario, Canada, after their breeding season. We recorded individual coordinates every 30 minutes, from the moment they emerged from their burrows around dusk until they burrowed in the morning, and obtained a total of 157 movements. We used the resulting series of step lengths and turning angles in a Hidden Markov Model to estimate movement type as ‘directed’ or ‘non-directed’. We also assigned to each encounter one of three space-dependent movement states: ‘foraging’, ‘in transit’, or ‘searching’, and found that movement type and state switched within individuals irrespective of time during a single night. We find that switching between movement types varied throughout the night, leading to stochastic within-individual variation in movements, and the distribution of movement distances differed significantly among individuals. Movement states, however, were time dependent, suggesting displacement routines were similar across individuals. Variation in movement behavior within individuals scales up to result in variation among individuals which, in turn, was found to shape the distribution of sampled individuals in the population. Our findings therefore underline the importance of a multi-scale approach in the study of movement.