title: Optimal orientation in flows: providing a benchmark for animal movement strategies.
abstract: Animal movements in air and water can be strongly affected by experienced flow. While various flow-orientation strategies have been proposed and observed, their performance in variable flow conditions remains unclear. We apply control theory to establish a benchmark for time-minimizing (optimal) orientation. We then define optimal orientation for movement in steady flow patterns and, using dynamic wind data, for short-distance mass movements of thrushes (Turdus sp.) and 6000 km non-stop migratory flights by great snipes, Gallinago media. Relative to the optimal benchmark, we assess the efficiency (travel speed) and reliability (success rate) of three generic orientation strategies: full compensation for lateral drift, vector orientation (single-heading movement) and goal orientation (continually heading towards the goal). Optimal orientation is characterized by detours to regions of high flow support, especially when flow speeds approach and exceed the animal's self-propelled speed. In strong predictable flow (short distance thrush flights), vector orientation adjusted to flow on departure is nearly optimal, whereas for unpredictable flow (inter-continental snipe flights), only goal orientation was near-optimally reliable and efficient. Optimal orientation provides a benchmark for assessing efficiency of responses to complex flow conditions, thereby offering insight into adaptive flow-orientation across taxa in the light of flow strength, predictability and navigation capacity.
authors: Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands j.d.mclaren@uva.nl.
authors: James D
authors: JD
authors: McLaren
authors: Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands.
authors: Judy
authors: J
authors: Shamoun-Baranes
authors: Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands Dutch Centre for Avian Migration and Demography, Department of Animal Ecology, Netherlands Institute for Ecology (NIOO-KNAW), Wageningen, The Netherlands.
authors: Adriaan M
authors: AM
authors: Dokter
authors: Dutch Centre for Avian Migration and Demography, Department of Animal Ecology, Netherlands Institute for Ecology (NIOO-KNAW), Wageningen, The Netherlands Dutch Montagu's Harrier Foundation, Animal Ecology Group, University of Groningen, Groningen, The Netherlands.
authors: Raymond H G
authors: RH
authors: Klaassen
authors: Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands.
authors: Willem
authors: W
authors: Bouten
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D046091:Charadriiformes / Q000502:physiology*; D005426:Flight, Animal / Q000502:physiology*; D008962:Models, Theoretical; D009949:Orientation / Q000502:physiology*; D020308:Songbirds / Q000502:physiology*; D013045:Species Specificity; D013997:Time Factors; D014919:Wind
keywords: animal navigation; flow orientation; lateral drift; migration; movement ecology; optimization