Scavengers on the Move: Behavioural Changes in Foraging Search Patterns during the Annual Cycle

Abstract

BackgroundOptimal foraging theory predicts that animals will tend to maximize foraging success by optimizing search strategies. However, how organisms detect sparsely distributed food resources remains an open question. When targets are sparse and unpredictably distributed, a Lévy strategy should maximize foraging success. By contrast, when resources are abundant and regularly distributed, simple Brownian random movement should be sufficient. Although very different groups of organisms exhibit Lévy motion, the shift from a Lévy to a Brownian search strategy has been suggested to depend on internal and external factors such as sex, prey density, or environmental context. However, animal response at the individual level has received little attention.Methodology/Principal FindingsWe used GPS satellite-telemetry data of Egyptian vultures Neophron percnopterus to examine movement patterns at the individual level during consecutive years, with particular interest in the variations in foraging search patterns during the different periods of the annual cycle (i.e. breeding vs. non-breeding). Our results show that vultures followed a Brownian search strategy in their wintering sojourn in Africa, whereas they exhibited a more complex foraging search pattern at breeding grounds in Europe, including Lévy motion. Interestingly, our results showed that individuals shifted between search strategies within the same period of the annual cycle in successive years.Conclusions/SignificanceResults could be primarily explained by the different environmental conditions in which foraging activities occur. However, the high degree of behavioural flexibility exhibited during the breeding period in contrast to the non-breeding period is challenging, suggesting that not only environmental conditions explain individuals' behaviour but also individuals' cognitive abilities (e.g., memory effects) could play an important role. Our results support the growing awareness about the role of behavioural flexibility at the individual level, adding new empirical evidence about how animals in general, and particularly scavengers, solve the problem of efficiently finding food resources.

Liberating Lévy walk research from the shackles of optimal foraging

“…The maximum likelihood estimate for the Lévy exponent is 1.8, and application of the Akaike information criterion indicates that a power-law distribution is convincingly favoured over both exponential and Gaussian distributions. Analogous results have also been reported for the movement patterns of the insectivorous bat, Myotis mystacinus, and the Egyptian vulture, Neophron percnopterus [196,197]. These observations are intriguing because they mirror observations of heavy-tailed velocity distributions in single cells, which also have Lévy walk movement patterns [102].…”

“…A new direction of travel is then chosen at random and the cycle repeats. regularly timed locational fixes, rather than between consecutive turns [195][196][197]. The former is a proxy for the velocity distribution while the latter is the standard hallmark of a Lévy walk.…”

Environmental drivers of variability in the movement ecology of turkey vultures (Cathartes aura) in North and South America

“…With a few notable exceptions (see [59]), previous studies of satellite-tracked birds have focused largely on migratory movements rather than on movements during the breeding and non-breeding seasons. Here, we highlight several findings from our turkey vulture dataset that suggest opportunities for future study of movements during non-migration periods.…”

Optimal foraging strategies: Lévy walks balance searching and patch exploitation under a very broad range of conditions

“…Benhamou, 2007;Oshanin et al, 2009;Plank and James, 2008;Plank and Codling, 2009;Raposo et al, 2003;Reynolds and Bartumeus, 2009;Reynolds and Rhodes, 2009), yet burgeoning empirical evidence of Lévy patterns in recorded animal movements (de Jager et al, 2011;Humphries et al, 2012;Humphries et al, 2010;López-López et al, 2013;Sims et al, 2012;Sims et al, 2008). Consequently, it seems appropriate to present a thorough exploration of Lévy walks as a foraging strategy with the aim of clarifying the conditions under which a Lévy walk provides an advantageous search pattern and gaining a better understanding of when such patterns might be observed in free-ranging animals.…”