Using Movement Ecology To Understand Flight Behavior In Soaring Birds
Understanding the process by which animals make decisions based on cues in their environment is a central challenge in behavioral ecology. We focus here on the process by which soaring migrant birds use landscape and weather features to make decisions during various aspects of flight. We examined how Tree Swallows weigh safety against speed in obstacleavoidance trials; how Turkey Vultures use artificial thermals to extend foraging past dusk; the movement ecology of migration in Turkey Vultures, including energetics, route choice, and use of surface features, turbulence, and winds; how migrating vultures vary in their use of these features according to whether they live in mountainous, flat, coastal, or inland environments; and how vultures vary in their use of weather features according to the time of year, and whether they are breeding, over-wintering, or migrating. To examine these questions, we employed a variety of experimental, computational, and statistical techniques. Birds were released in flight tunnels for obstacle avoidance trials, while vultures were implanted with heart rate loggers and tracked via satellite-based GPS to study movements. Weather variables were drawn from the North American Regional Reanalysis, a regional-scale meteorological model. In obstacle avoidance trials, we found no evidence that swallows exhibit side-bias to promote quick decision making. We found that, in nature, Turkey Vultures will forage past their normal daily activity period when presented with both an artificial food source and an artificial thermal, in the form of a methane-vent. A heart rate analysis of a migrating turkey vulture suggests that the act of migration is not energetically costly for soaring migrants. An analysis of movement paths in relation to turbulence, horizontal winds, terrain ruggedness, and other descriptors such as heat flux and boundary layer height shows that movement and navigation correlates with a variety of external factors, most notably turbulent kinetic energy, horizontal winds, and surface ruggedness. We found that the way in which vultures use weather features depends on the time of year, biological motivation, the presence of mountain ranges, and the way in which these variables interact with each other.
Flight behavior in Birds
dissertation or thesis