Movement strategies for large-scale displacements in Vulturine guineafowl (Acryllium vulturinum)

Dispersal—the process by which individuals depart their natal range, transit through the environment, and settle into new areas—is one of the most fundamental and pervasive life history phases in the animal kingdom. Typically, dispersal is motivated by individuals’ need to avoiding breeding—and competing—with kin, or to secure access to the resources necessary to reproduce. In order to reap the benefits of dispersing, individuals often have to travel large distances—a process which can be subject to constraints on behavior and impose significant physiological costs. For dispersal to retain its adaptive value, selection should therefore favor behaviors which mitigate the costs of dispersing. In this thesis, I aimed to understand how the behavior of dispersing animals reflects the costs that they face in making such large movements, with the ultimate goal of understanding the strategies that have evolved to overcome these costs.Much of the study of dispersal to date has focused on individuals’ decisions to depart or settle in a given area. By contrast, there has been relatively little attention paid to the movements of transient individuals, despite transience being the active component of dispersal, and encompassing many of its associated behaviors. Many of the greatest barriers to successful dispersal are thought to be most present during this active stage, from increased risks of predation, to energy use, to navigational challenges. By investigating not only where, but how and when dispersers move while transient, research into this critical stage of dispersal will prove key to understanding how animals respond to these costs. However, studying transience behaviors is a particularly difficult endeavor, not only because of the challenge of tracking dispersing individuals, but also because of the need to establish a meaningful frame of reference against which to evaluate these behaviors. In this thesis, I studied the dispersal movements of transient animals through the use of high-resolution GPS tracking devices deployed in a wild population of free ranging vulturine guineafowl (Acryllium vulturinum) in Laikipia county, Kenya. In each of my chapters, I examined the changes in movement behaviors exhibited by transient individuals, and drew inferences about the strategies that they express by making direct comparisons between dispersing individuals’ behavior across different stages, and between dispersing and non-dispersing birds in similar time frames.In my first chapter, I integrated high-resolution GPS data with physiological models of the metabolic costs of movement to test a long-standing hypothesis that dispersal should be an energetically-costly endeavor given the distances that dispersers traverse. I hypothesized that such costs are result of 4 how animals move, and not only how far. My results show that dispersing animals are able to substantially increase the energetic efficiency of their movements during their transience period, primarily as a result of distinct changes in the speed and straightness of their movements.In my second chapter, I further examined the fine-scale changes in how dispersing animals move, using their diel patterns of movement as lens into the ways that ecological constraints affect when and how they move. A wide array of ecological constraints, from predation risks to elevated temperatures, can limit animals’ movements, resulting in distinct diel cycles with peaks and valleys in activity. I first proposed a general framework to help make inference about how animals might respond to constraints on movement, and predicted three possible patterns of correlation between the timing of dispersers’ normal movements and when they make the largest movements during dispersal. My results show that guineafowl express a positive correlation between the times when they typically move most, and the hours when they make the largest increases in their movement, suggesting that the ecological effects that constrain their movements outside of dispersal persist during transience.Finally, in my third chapter, I built upon the findings of chapter one by using the efficient movements of dispersing animals as a lens through which to re-examine the costs of movement in group-living animals. By extracting the largest movements made by groups, and comparing them to the highly-efficient movements of lone dispersers, I was able to test whether individuals’ capacity for efficient movements is constrained when moving as part of a collective. I found that individuals in groups are able to increase the energetic efficiency of their movements when making large collective movements, but that the scale of this increase is substantially less than that achieved by lone individuals, revealing a previously hidden cost of group living. These results also further highlight the strength of selection for efficient movement during dispersal.Together, these three chapters form the basis for a for a new understanding of the factors driving the evolution of strategies that allow animals to achieve extraordinary, landscape-scale movements, and the fine-scale, moment-by-moment behaviors that animals express in the face of significant energetic, environmental, and social constraints.publishe