Mixed strategies of griffon vultures' (Gyps fulvus) response to food deprivation lead to a hump-shaped movement pattern

Orr Spiegel*, Roi Harel, Wayne M. Getz, Ran Nathan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

65 Scopus citations


Background: The need to obtain food is a critical proximate driver of an organism's movement that shapes the foraging and survival of individual animals. Consequently, the relationship between hunger and foraging has received considerable attention, leading to the common conception that hunger primarily enhances a "food-intake maximization" (FIMax) strategy and intensive search. A complementary explanation, however, suggests a trade-off with precautions taken to reduce the risk of physiological collapse from starvation, under a strategy we denote as "energy-expenditure minimization" (EEMin). The FImax-EEmin trade-off may interact with the forager's hunger level to shape a complex (non-monotonic) response pattern to increasing hunger. Yet, this important trade-off has rarely been investigated, particularly in free-ranging wild animals. We explored how hunger affects the movements of adult griffon vultures (Gyps fulvus) in southern Israel. Transmitters combining GPS and accelerometers provided high-resolution data on vultures' movements and behavior, enabling the identification of feeding events and the estimation of food deprivation periods (FDPs, measured in days), which is used as a proxy for hunger. Results: Data from 47 vultures, tracked for 339±36days, reveal high variability in FDPs. While flight speed, flight straightness and the proportion of active flights were invariant in relation to food deprivation, a clear hump-shaped response was found for daily flight distances, maximal displacements and flight elevation. These movement characteristics increased during the first five days of the FDP sequence and decreased during the following five days. These characteristics also differed between short FDPs of up to four days, and the first four days of longer FDP sequences. These results suggest a switch from FIMax to EEMin strategies along the FDP sequence. They also indicate that vultures' response to hunger affected the eventual duration of the FDP. During winter (the vultures' incubation period characterized by unfavorable soaring meteorological conditions), the vultures' FIMax response was less intensive and resulted in longer starvation periods, while, in summer, more intensive FIMax response to hunger resulted in shorter FDPs. Conclusions: Our results show a flexible, non-monotonic response of free-ranging wild animals to increasing hunger levels, reflecting a trade-off between increasing motivation to find food and the risk of starvation. The proposed trade-off offers a unifying perspective to apparently contradictory or case-specific empirical findings.

Original languageAmerican English
Article number5
JournalMovement Ecology
Issue number1
StatePublished - 5 Jul 2013

Bibliographical note

Funding Information:
The authors wish to thank the Israeli Nature Protection Authority for a long and fruitful cooperation. For invaluable help during fieldwork, special thanks are due to the following NPA staff: A. Atar, A. Basbusa-Rashaide, A. Zabari, B. Woodley, D. Zackai, O. Goelman, O. Yahalomi, Y. Miller, Y. Sinai and, above all, to O. Hatzofe. We are also grateful to F. Kuemmeth and W. Heidrich and the members of the Movement Ecology Laboratory, and especially Y. Bartan for their help at various phases of the research. The manuscript also benefited from comments by N. Ben-Eliahu, L. Borger, K. Bildstein and two anonymous reviewers. This research was supported by a NIH grant GM083863 to WMG and by the U.S.–Israel Bi-national Science Foundation (BSF 255 ⁄ 2008) and the special BSF Multiplier Grant Award from the Rosalinde and Arthur Gilbert Foundation to RN and WMG. We also acknowledge funding from the Rothschild Fellowship of Yad Hanadiv and the Eshkol Fellowship of the Israeli Ministry of Science to OS, from the Adelina and Massimo Della Pergola Chair of Life Sciences and the Friedrich-Wilhelm-Bessel Research Award of the Humboldt Foundation to RN.

Publisher Copyright:
© 2013 Spiegel et al.; licensee BioMed Central Ltd.


  • Fasting period
  • GPS-ACC tracking
  • Internal motivation
  • Movement ecology
  • Non-linear response
  • Optimal foraging
  • Starvation risks
  • Supplementary feeding management
  • Vulture conservation


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