The magnetite-based receptors in the beak of birds and their role in avian navigation

R Wiltschko,W Wiltschko

doi:10.1007/s00359-012-0769-3

Abstract

Iron-rich structures have been described in the beak of homing pigeons, chickens and several species of migratory birds and interpreted as magnetoreceptors. Here, we will briefly review findings associated with these receptors that throw light on their nature, their function and their role in avian navigation. Electrophysiological recordings from the ophthalmic nerve, behavioral studies and a ZENK-study indicate that the trigeminal system, the nerves innervating the beak, mediate information on magnetic changes, with the electrophysiological study suggesting that these are changes in intensity. Behavioral studies support the involvement of magnetite and the trigeminal system in magnetoreception, but clearly show that the inclination compass normally used by birds represents a separate system. However, if this compass is disrupted by certain light conditions, migrating birds show ‘fixed direction’ responses to the magnetic field, which originate in the receptors in the beak. Together, these findings point out that there are magnetite-based magnetoreceptors located in the upper beak close to the skin. Their natural function appears to be recording magnetic intensity and thus providing one component of the multi-factorial ‘navigational map’ of birds.

Highlights

The literature on the avian magnetic compass, showing its functional properties, the underlying physical radical pair processes and its association with the visual system, has been discussed in several recent reviews (e.g., Ritz et al 2010; Ritz 2011; W. Wiltschko et al 2011)
These findings provide some information on the receptors in question: the effect of the strong, short magnetic pulse on the orientation of birds indicates that the receptors are based on magnetic material like magnetite
Zapka et al (2009) obtained similar results by cutting the ophthalmic nerve. All these findings clearly show that the magnetite-based receptors are not involved in the avian magnetic compass

Summary

Introduction

The literature on the avian magnetic compass, showing its functional properties, the underlying physical radical pair processes and its association with the visual system, has been discussed in several recent reviews (e.g., Ritz et al 2010; Ritz 2011; W. Wiltschko et al 2011). The literature on the avian magnetic compass, showing its functional properties, the underlying physical radical pair processes and its association with the visual system, has been discussed in several recent reviews Wiltschko et al 2011). The other avian magnetoreception system, based on magnetite and associated with the trigeminal system, has received less attention and has not been summarized in a review so far. We will describe the respective findings, mostly behavioral that support the existence of magnetite-based magnetoreceptors in the beak of birds and provide some insight in their structure, their function and their role in avian navigation

Biogenic magnetite and its possible role in magnetoreception

Magnetite found in birds

The pioneering studies by Beason and Semm

Pulse experiments to indicate magnetite

What kind of information is mediated?

Conclusion