AMoveE 2014: Orr Spiegel
Channel: Movebank
Date: 2014-05-23

This talk was presented by Orr Spiegel on 7 May 2014 as part of the Symposium on Animal Movement and the Environment, held at the North Carolina Museum of Natural Sciences in Raleigh.

Spiegel O, Harel R, Centeno-Cuadros A, Hatzofe O, Getz WM, Nathan R, 2014, "Moving beyond curve-fitting: complementary evidence on vultures' long-range forays contradicts Lévy foraging hypothesis"

Abstract: Animal movements exhibit an almost universal pattern of fat-tailed step-size distributions. The Lévy flight foraging hypothesis asserts that this pattern reflects an optimal search strategy for unpredictable sparse resources, combining many short steps of local search with rare and much longer steps of inter-patch movements. Despite empirical and theoretical support, this hypothesis remains controversial and alternative explanations have rarely been tested with complementary data. To confront alternative explanations for observed fat-tailed distributions, we tracked three vulture species (Gyps fulvus, G. africanus and Torgos tracheliotus) in two very different ecosystems in Africa and the Middle East using high-resolution GPS/accelerometer tags accompanied by behavioral, genetic and morphological data for G. fulvus. Maximum-likelihood estimation of alternative probability density functions revealed fat-tailed step-size distributions with three distinct superimposed movement modes for all species. These modes, with characteristic scales of reorientation every 46--83m, 2--4km and 12--31km, respectively corresponded to (i) local moves and stops, (ii) foraging flights within core parts of the home range, and (iii) long-range movements outside the core area. The latter include long-range forays (LRFs)—short-term, large-scale circular journeys exceeding beyond the typical foraging range—that contributed to the observed fat-tailed pattern. Nevertheless, analysis of the complementary behavioral and energy expenditure data reveal that vultures' LRFs entail high energy costs and low food intake, thus contrasting the most basic expectations of the Lévy foraging hypothesis. Analyses of additional morphological, meteorological and genetic datasets, refuted alternative LRF explanations based on preferred weather conditions or population genetic structure. In contrast, female biased sex ratios, distinct seasonality (pre-breeding period) and behavior (frequent roost alternation at the LRFs wandering phase) jointly suggest that LRFs in these species might represent failed breeding dispersal attempts to find mates at remote colonies. We conclude that inference about the mechanisms underlying commonly observed movement patterns should always be confronted with data other than just spatial locations and call for investigating the hypothesis invoking superposition of distinct behavioral movement modes as a general explanation for animals fat-tailed step-size distributions.