Night-migratory garden warblers can orient with their magnetic compass using the left, the right or both eyes - PubMed (original) (raw)

Night-migratory garden warblers can orient with their magnetic compass using the left, the right or both eyes

Christine Maira Hein et al. J R Soc Interface. 2010.

Abstract

Several studies have suggested that the magnetic compass of birds is located only in the right eye. However, here we show that night-migrating garden warblers (Sylvia borin) are able to perform magnetic compass orientation with both eyes open, with only the left eye open and with only the right eye open. We did not observe any clear lateralization of magnetic compass orientation behaviour in this migratory songbird, and, therefore, it seems that the suggested all-or-none lateralization of magnetic compass orientation towards the right eye only cannot be generalized to all birds, and that the answer to the question of whether magnetic compass orientation in birds is lateralized is probably not as simple as suggested previously.

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Figures

Figure 1.

Figure 1.

ZENK activation, which mirrors neuronal activation in cluster N, is reduced to a background level when garden warblers wore hoods covering both eyes. (a) Schematic drawing of cluster N (area within dashed line). (b,c) Photos of sagittal brain slices through the centre of cluster N stained against ZENK protein. (b) ZENK activation of cluster N in a garden warbler that had both eyes open. The small black dots are ZENK-positive neuron nuclei, i.e. these neurons were active when a garden warbler had both eyes open during the night under the dim-light conditions of our wooden testing huts. (c) ZENK activation of cluster N in a garden warbler that wore one of our hoods covering both eyes. Notice that the ZENK activation level and thus the number of active neurons are reduced to the background level. Consequently, our hoods are light-tight and seem to effectively block input to the brain area cluster N, which is required for magnetic compass orientation and which seems to be involved in the processing of magnetic compass information (Zapka et al. 2009). Scale bar in (a) (for a_–_c) = 400 µm. DNH, dorsal nucleus of the hyperpallium; H, hyperpallium; MD, mesopallium dorsale; MV, mesopallium ventrale; N, nidopallium.

Figure 2.

Figure 2.

Control experiments showed that the birds were in migratory mood and able to perform magnetic compass orientation. (a) Our garden warblers oriented in their typical south-westerly migratory direction in autumn in the NMF when no hood was attached to their head. (b) The same birds’ orientation without hoods in a magnetic field turned 120° counterclockwise (CMF). mN, magnetic North. The arrows indicate the group mean vectors. The inner and outer dashed circles indicate the radius of the group mean vector needed for directional significance according to the Rayleigh test (p < 0.05 and p < 0.01, respectively). The radial lines flanking the group mean vector indicate the 95% confidence intervals for the group mean direction.

Figure 3.

Figure 3.

Garden warblers wearing hoods can use their magnetic compass if light and/or visual input reaches any one eye. (a,b) The results from birds equipped with hoods with an 8 mm diameter hole in front of both eyes. (c,d) The results from birds equipped with hoods allowing light and visual input to reach only the left eye. (e,f) The results from birds equipped with hoods allowing light and visual input to reach only the right eye. The data in (a,c,e) were collected in an unchanged magnetic field (NMF). The data in (b,d,f) were collected in a magnetic field turned 120° counterclockwise (CMF). mN, magnetic North. For a description of the circular diagrams, see the legend to figure 2.

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