Magnetic map navigation in a migratory songbird requires trigeminal input

Abstract

Recently, virtual magnetic displacement experiments have shown that magnetic cues are indeed important for determining position in migratory birds; but which sensory system(s) do they use to detect the magnetic map cues? Here, we show that Eurasian reed warblers need trigeminal input to detect that they have been virtually magnetically displaced. Birds with bilaterally ablated ophthalmic branches of the trigeminal nerves were not able to re-orient towards their conspecific breeding grounds after a virtual magnetic displacement, exactly like they were not able to compensate for a real physical displacement. In contrast, sham-operated reed warblers re-oriented after the virtual displacement, like intact controls did in the past. Our results show that trigeminally mediated sensory information is necessary for the correct function of the reed warblers' magnetic positioning system.

Figure 1

Centre: map of natural magnetic field parameters of the capture site (Rybachy, Kaliningrad region) and the site of virtual displacement (Zvenigorod, Moscow region). The solid arrow on the map shows the virtual displacement direction and distance. The red and blue lines on the map are the magnetic declination and magnetic intensity isolines, respectively. The circular diagrams show the orientation of the Eurasian reed warblers tested at the capture site before surgical treatment and virtual displacement ((A) real V1-sectioned group, (B) sham-sectioned group) and the same birds’ orientation after a purely magnetic 1,000 km virtual eastward displacement ((C) V1-sectioned group, (D) sham-operated group). Each dot at the circle periphery indicates the mean orientation of one individual bird; arrows show mean group vectors; the dashed circles indicate the radius of the group mean vector needed for 5% and 1% levels of significance according to the Rayleigh test of uniformity; solid lines flanking mean group vectors give 95% confidence intervals for the group mean directions. Geographic North corresponds to 0°, magnetic North (mN) is shown by a red triangle outside the circle (+5.5° declination in Rybachy and +10.1° declination in Zvenigorod). The map was produced in R 3.2.5 (R Foundation for Statistical Computing, http://www.R-project.org/) using packages “map”, “mapproj” and “mapdata”.