Factors influencing foraging search efficiency: Why do scarce lappet-faced vultures outperform ubiquitous white-backed vultures?

Orr Spiegel*, Wayne M. Getz, Ran Nathan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

62 Scopus citations


The search phase is a critical component of foraging behavior, affecting interspecific competition and community dynamics. Nevertheless, factors determining interspecific variation in search efficiency are still poorly understood. We studied differences in search efficiency between the lappet-faced vulture (Torgos tracheliotus; LFV) and the white-backed vulture (Gyps africanus; WBV) foraging on spa-tiotemporally unpredictable carcasses in Etosha National Park, Namibia. We used experimental food supply and high-resolution GPS tracking of free-ranging vultures to quantify search efficiency and elucidate the factors underlying the observed interspecific differences using a biased correlated random walk simulation model bootstrapped with the GPS tracking data. We found that LFV's search efficiency was higher than WBV's in both first-to-find, first-to-land, and per-individual-finding rate measures. Modifying species-specific traits in the simulation model allows us to assess the relative role of each factor in LFV's higher efficiency. Interspecific differences in morphology (through the effect on perceptual range and motion ability) and searchers' spatial dispersion (due to different roost arrangements) are in correspondence with the empirically observed advantage of LFV over WBV searchers, whereas differences in other aspects of the movement patterns appear to play a minor role. Our results provide mechanistic explanations for interspecific variation in search efficiency for species using similar resources and foraging modes.

Original languageAmerican English
Pages (from-to)E102-E115
JournalAmerican Naturalist
Issue number5
StatePublished - May 2013


  • Avian visual acuity
  • Individual-based simulation model
  • Interspecific competition
  • Movement ecology
  • Optimal foraging
  • Vulture conservation


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