On the role of topography and atmospheric conditions to support efficient movement : How flying animals use the energy in the landscape to travel efficiently

Abstract

Movement is a scale-dependent process which permeates all aspects of life on Earth. Depending on the scale at which we observe movement in its external context, we will notice that this can be facilitated or constrained by different factors, which in the case of humans and animals, translates to a change of the energetic cost required to move between two locations. During my PhD I investigated factors in the physical environments that can define the energetic cost of movement through the landscape based on previously collected bio-logging data. I focused on flying animals, as the three-dimensional aerial environment in which they move is complex and extremely dynamic, constantly providing animals moving in this medium with challenges and opportunities to remain aloft. The advances in bio-logging devices currently allow us to record animal movement at extremely high spatial and temporal resolution. However, the comparability of data collected with different methodologies is rarely investigated. I therefore focused the first chapter of my thesis on testing the comparability of movement data collected through two common types of device attachments, to pool data from different studies. I dedicated the other three chapters of my thesis to investigate the proportion in which topography and atmospheric conditions contribute to creating potential energy in the environment, allowing flying animals across taxa to travel with low energetic cost. I first focused on soaring birds, which strongly rely on environmental support - in terms of vertical air currents - to move across the landscape. I finally applied a similar methodology and research questions to bats, a completely different study system in which the role of environmental support during flight had been largely overlooked. My PhD work suggests that both weather and static landscape features contribute to creating energy in the landscape. It hints to the existence of converging patterns in the way taxonomically distant species use the potential energy available in the landscape to fly efficiently. At the same time, it highlights the species-specificity of energy landscapes, according to which the same landscape provides different species with different low-cost flight opportunities, depending on their behaviour, morphology and on their ability to interpret the landscape. From a methodological and applied perspective, this translates to the need of different combination of environmental parameters to predict the flight behaviour of different species, with clear consequences for their conservation. Finally, my results show that the different contributions of weather versus static landscape features are also a consequence of the spatial and temporal resolution at which these environmental information are available. This highlights the scale-dependent nature of the movement process and the importance of matching the scale and resolution at which the movement phenomenon and its environmental context are observed and investigated.