Modeling raptor migration pathways using a fluid-flow analogy

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Modeling raptor migration pathways using a fluid-flow analogy

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Title: Modeling raptor migration pathways using a fluid-flow analogy
Author: Brandes, David; Ombalski, D. W.
Abstract: We describe an approach to mathematical modeling of raptor migration nuclei-conditions in which terrain updrafts are the primary source of lift. The model is based on the analogy of laminar fluid flow to raptor migration, with the assumption that migration flux at. a particular location is proportional to terrain conductivity and the local energy gradient driving migration. The terrain conductivity parameter is taken to be the relative updraft strength, which is calculated using wind direction, terrain slope, and terrain aspect data determined from a digital-elevation model of the area of interest. By imposing a directional energy gradient (a preferred axis of migration [PAM]) across the resulting conductivity field, flow (i.e., migration) is generated, and the predominant migration paths through the region are determined. We apply the model by simulating the spring migration of Golden Eagles (Aquila chrysaetos) through central Pennsylvania under eight different wind scenarios. The locations of the simulated migration tracks depended on wind direction, PAM direction, and the spatial arrangement and orientation of terrain features. Migration tracks showed a marked tendency to converge toward a small number of preferred pathways as the migration proceeds. The overall pattern of simulated migration was consistent with available count data. Model results showed that south/southeast and north/northwest winds provided the best conditions for rapid migration across the region, as was suggested by field data.
URI: http://hdl.handle.net/10385/915
Date: 2004

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