Elsevier

Animal Behaviour

Volume 71, Issue 1, January 2006, Pages 183-191
Animal Behaviour

Experimental evidence for a magnetic sense in Neotropical migrating butterflies (Lepidoptera: Pieridae)

https://doi.org/10.1016/j.anbehav.2005.04.013 Get rights and content

We tested whether migrating Aphrissa statira butterflies orient with a magnetic compass. We captured migrants flying over Lake Gatún, Panama, and exposed experimental butterflies to a strong magnetic field. These and unmanipulated control butterflies were released back over the lake. Experimental butterflies had a more dispersed pattern of orientation than control butterflies. The average direction adopted was northeast, 160° anticlockwise to the natural migratory direction. Unmanipulated control butterflies adopted two diametrically opposed orientations: one shifted 33° clockwise, and another 147° anticlockwise, to the migratory direction. Control and experimental butterflies differed in that some controls oriented towards the migratory direction. These differences in orientation support the hypothesis of a sense for magnetic orientation cues. Unmanipulated butterflies released over the lake when the sky was completely overcast were significantly oriented towards their direction before capture (187° and 203°, respectively), further supporting the magnetic compass hypothesis. In a third experiment, we obstructed sun compass cues and reversed the horizontal component of the local geomagnetic field to position magnetic north towards the geographical south pole within a flight arena into which we released individual butterflies. Experimental butterflies experiencing the reversed magnetic field oriented on average 180° opposite to their natural migratory direction. Control butterflies, for which the position of magnetic north was unaltered, were oriented both towards and 180° opposite to the natural migratory direction. This difference between orientations of control and experimental butterflies also supports the hypothesis of a sense for magnetic orientation cues.

Section snippets

Experimental disruption of the magnetic sense

Information that arises from the geomagnetic field may be disrupted by application of a strong magnetic field. This technique has been used successfully with migrating passerine birds (Wiltschko et al. 1994) and monarch butterflies (Perez et al. 1999). We applied a strong magnetic field to experimental butterflies, whereas a control group was handled in the same manner but a strong magnetic field was not applied. We predicted that unmanipulated control butterflies would adopt the natural

Natural Flight Directions

We captured butterflies flying over the Panama Canal (Lake Gatún) between 0900 and 1200 hours for midday experiments and for experiments the following morning (refer to Srygley et al. 1996 for a map of the flyway and Oliveira et al. 1998 for the phenology of the Aphrissa migration). Data were collected during the migratory seasons of 2001, 2002 and 2003 (specifically 24 June–7 July 2001, 13 May–23 July 2002 and 21 May–6 June 2003). Prior to capture of each butterfly as it migrated naturally

Strong Magnet Experiments

When released, control butterflies were significantly oriented on an axis (68° and 248°; axial analysis, Rayleigh test: r = 0.36, N = 57, P < 0.01; Fig. 1a). Before capture, these same butterflies had a mean orientation of 215° (±9°, 95% confidence interval; Fig. 1b). The 95% confidence interval for the released control butterflies (±28°) overlapped with the 95% confidence interval of the mean orientation before capture, but their axial orientation upon release was obviously different from their

Discussion

We have presented experimental evidence for a magnetic sense in migratory A. statira butterflies. Orientations of butterflies experimentally exposed to a strong magnetic field were significantly more dispersed than those of control butterflies. Significant differences between experimental and control groups indicate behavioural sensitivity to magnetic perturbation, although additional factors pertain in the interpretation of the orientational distributions. In addition, butterflies released

Acknowledgments

This research was funded with a grant from the National Geographic Society Committee for Research and Exploration. In addition, R.B.S. was supported by a Senior Postdoctoral Fellowship from the Smithsonian Institution Office of Fellowships and Grants, Washington, DC and the Korean Science and Engineering Foundation supported preparation of the manuscript. E.G.O. was supported by a CNPq Postdoctoral Fellowship. We thank the National Geographic Society and the Smithsonian Tropical Research

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  • Cited by (0)

    1

    R. Dudley is at the Department of Integrative Biology, University of California-Berkeley, Berkeley, CA 94720-3140, U.S.A.

    2

    E. G. Oliveira is at the Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, 30161-970 Belo Horizonte, MG, Brazil.

    3

    A. J. Riveros is now at the Center for Insect Science, Arizona Research Laboratories, University of Arizona, 611 Gould-Simpson Science Building, 1040 E. Fourth, Tucson, AZ 35721-0101, U.S.A.

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