Abstract
The gravity vector theory postulates that birds determine their position to set a home course by comparing the memorized gravity vector at the home loft with the local gravity vector at the release site, and that they should adjust their flight course to the gravity anomalies encountered. As gravity anomalies are often intermingled with geomagnetic anomalies, we released experienced pigeons from the center of a strong circular gravity anomaly (25 km diameter) not associated with magnetic anomalies and from a geophysical control site, equidistant from the home loft (91 km). After crossing the border zone of the anomaly – expected to be most critical for pigeon navigation – they dispersed significantly more than control birds, except for those having met a gravity anomaly en route. These data increase the credibility of the gravity vector hypothesis.
FOOTNOTES
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Author contributions
H.-P.L. and V.K. conceived and designed the experiments; N.B. and H.P.L. performed the experiments; N.B., S.G., H.P.L. and D.P.W. analyzed the data; S.G. and V.E. assembled geophysical maps and analyzed pigeon tracks; N.B. and H.-P.L. wrote the manuscript; H.-P.L. created the supplementary graphs.
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Competing interests
The authors declare no competing financial interests.
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Funding
Swiss National Science Foundation (SNF 31-122589), SCOPES IZ73Z0_128166 (Swiss-Ukrainian Research Cooperation), and intramural funds of the University of Zürich (F-41002-01-01).
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Supplementary material
Supplementary material available online at http://jeb.biologists.org/lookup/suppl/doi:10.1242/jeb.108670/-/DC1
- © 2014. Published by The Company of Biologists Ltd
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