## Journal article: Moving beyond Curve Fitting : Using Complementary Data to Assess Alternative Explanations for Long Movements of Three Vulture Species

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February 2015
Spiegel, Orr
Getz, Wayne M.
Nathan, Ran
Journal article
Published
##### Abstract
Animal movements exhibit an almost universal pattern of fat-tailed step-size distributions, mixing short and very long steps. The Lévy flight foraging hypothesis (LFFH) suggests a single optimal food search strategy to explain this pattern, yet mixed movement distributions are biologically more plausible and often convincingly fit movement data. To confront alternative explanations for these patterns, we tracked vultures of three species in two very different ecosystems using high-resolution global positioning system/accelerometer tags accompanied by behavioral, genetic, and morphological data. The Lévy distribution fitted the data sets reasonably well, matching expectations based on their sparsely distributed food resources; yet the fit of mixed models was considerably better, suggesting distinct movement modes operating at three different scales. Specifically, long-range forays (LRFs)—rare, short-term, large-scale circular journeys that greatly exceed the typical foraging range and contribute to the tail-fatness of the movement distribution in all three species—do not match an optimal foraging strategy suggested by the LFFH. We also found no support for preferred weather conditions or population genetic structure as alternative explanations, so the hypothesis that LRFs represent failed breeding dispersal attempts to find mates remains our most plausible explanation at this time. We conclude that inference about the mechanisms underlying animal movements should be confronted with complementary data, and suggest that mixed behavioral modes likely explain commonly observed fat-tailed movement distributions.
##### Subject (DDC)
570 Biosciences, Biology
##### Keywords
movement ecology, Lévy flight foraging hypothesis, sexbiased dispersal, fat-tailed step-size distribution, wildlife biotelemetry, 3-D accelerometers
##### Published in
The American Naturalist ; 185 (2015), 2. - pp. E44-E54. - University of Chicago Press. - ISSN 0003-0147. - eISSN 1537-5323
##### Cite This
ISO 690SPIEGEL, Orr, Roi HAREL, Alejandro CENTENO-CUADROS, Ohad HATZOFE, Wayne M. GETZ, Ran NATHAN, 2015. Moving beyond Curve Fitting : Using Complementary Data to Assess Alternative Explanations for Long Movements of Three Vulture Species. In: The American Naturalist. University of Chicago Press. 185(2), pp. E44-E54. ISSN 0003-0147. eISSN 1537-5323. Available under: doi: 10.1086/679314
BibTex
@article{Spiegel2015-02Movin-51506,
year={2015},
doi={10.1086/679314},
title={Moving beyond Curve Fitting : Using Complementary Data to Assess Alternative Explanations for Long Movements of Three Vulture Species},
number={2},
volume={185},
issn={0003-0147},
journal={The American Naturalist},
pages={E44--E54},
author={Spiegel, Orr and Harel, Roi and Centeno-Cuadros, Alejandro and Hatzofe, Ohad and Getz, Wayne M. and Nathan, Ran}
}

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<dcterms:abstract xml:lang="eng">Animal movements exhibit an almost universal pattern of fat-tailed step-size distributions, mixing short and very long steps. The Lévy flight foraging hypothesis (LFFH) suggests a single optimal food search strategy to explain this pattern, yet mixed movement distributions are biologically more plausible and often convincingly fit movement data. To confront alternative explanations for these patterns, we tracked vultures of three species in two very different ecosystems using high-resolution global positioning system/accelerometer tags accompanied by behavioral, genetic, and morphological data. The Lévy distribution fitted the data sets reasonably well, matching expectations based on their sparsely distributed food resources; yet the fit of mixed models was considerably better, suggesting distinct movement modes operating at three different scales. Specifically, long-range forays (LRFs)—rare, short-term, large-scale circular journeys that greatly exceed the typical foraging range and contribute to the tail-fatness of the movement distribution in all three species—do not match an optimal foraging strategy suggested by the LFFH. We also found no support for preferred weather conditions or population genetic structure as alternative explanations, so the hypothesis that LRFs represent failed breeding dispersal attempts to find mates remains our most plausible explanation at this time. We conclude that inference about the mechanisms underlying animal movements should be confronted with complementary data, and suggest that mixed behavioral modes likely explain commonly observed fat-tailed movement distributions.</dcterms:abstract>
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