Decision-making by a soaring bird: time, energy and risk considerations at different spatio-temporal scales

Abstract

One contribution of 17 to a theme issue 'Moving in a moving medium: new perspectives on flight'. Natural selection theory suggests that mobile animals trade off time, energy and risk costs with food, safety and other pay-offs obtained by movement. We examined how birds make movement decisions by integrating aspects of flight biomechanics, movement ecology and behaviour in a hierarchical framework investigating flight track variation across several spatio-temporal scales. Using extensive global positioning system and accelerometer data from Eurasian griffon vultures (Gyps fulvus) in Israel and France, we examined soaring-gliding decision-making by comparing inbound versus outbound flights (to or from a central roost, respectively), and these (and other) homerange foraging movements (up to 300 km) versus long-range movements (longer than 300 km). We found that long-range movements and inbound flights have similar features compared with their counterparts: individuals reduced journey time by performing more efficient soaring -gliding flight, reduced energy expenditure by flapping less and were more risk-prone by gliding more steeply between thermals. Age, breeding status, wind conditions and flight altitude (but not sex) affected time and energy prioritization during flights. We therefore suggest that individuals facing time, energy and risk trade-offs during movements make similar decisions across a broad range of ecological contexts and spatial scales, presumably owing to similarity in the uncertainty about movement outcomes.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'.

Moving in a moving medium: new perspectives on flight

“…The results are consistent with a strategy to reduce the aerodynamic costs of transport in relation to headwinds. Flight speeds were also among the parameters quantified by Harel et al [20] in rich, long-term and high-resolution movement datasets from Eurasian griffon vultures (Gyps fulvus). These authors compared three proxies of time, energy and risk minimization across three spatio-temporal scales, ranging from seconds and metres, to months and thousands of kilometres.…”

“…These simulations provide new opportunities for understanding the world in which animals fly, incorporating not only the mean flow, but also the variability and predictability of that flow. Such high-resolution eddy-resolving simulations are computationally expensive and primarily research tools, however lower resolution simulations (of the order of a few kilometres resolution and Harel et al [20] use RAMS with a spatial resolution of 1 km and temporal resolution of 5 minutes) are now run routinely both for general weather forecasting (e.g. the UK Met Office forecast model runs at 1.5 km resolution), and specifically for forecasting flight conditions for glider pilots (e.g.…”

“…The behavioural responses of animals to variable airflows, in terms of route and speed selection could potentially inform UAV flight path planning in this regard, particularly as their responses probably represent strategies that reconcile different currencies of risk and cost minimization (cf. [20,38]). …”

Meteorological and environmental variables affect flight behaviour and decision‐making of an obligate soaring bird, the California Condor Gymnogyps californianus

“…, Harel et al . ), trained Himalayan Griffon Vultures Gyps himalayensis in France (Duriez et al . ), and Turkey Vultures Cathartes aura in North America (Mandel et al .…”

“…Specialists and generalists also differ in how they trade off risks against constraints linked to time and energy (Hedenström , Alerstam & Hedenström , Harel et al . , Miller et al . ).…”