Avian magnetoreception: elaborate iron mineral containing dendrites in the upper beak seem to be a common feature of birds.

Gerald Falkenberg,Gerta Fleissner,Peter Thalau,Kirsten Schuchardt,Guenther Fleissner,Gerd Wellenreuther,Dominik Heyers,Henrik Mouritsen,Markus Kuehbacher,Eric Warrant

doi:10.1371/journal.pone.0009231

Abstract

The magnetic field sensors enabling birds to extract orientational information from the Earth's magnetic field have remained enigmatic. Our previously published results from homing pigeons have made us suggest that the iron containing sensory dendrites in the inner dermal lining of the upper beak are a candidate structure for such an avian magnetometer system. Here we show that similar structures occur in two species of migratory birds (garden warbler, Sylvia borin and European robin, Erithacus rubecula) and a non-migratory bird, the domestic chicken (Gallus gallus). In all these bird species, histological data have revealed dendrites of similar shape and size, all containing iron minerals within distinct subcellular compartments of nervous terminals of the median branch of the Nervus ophthalmicus. We also used microscopic X-ray absorption spectroscopy analyses to identify the involved iron minerals to be almost completely Fe III-oxides. Magnetite (Fe II/III) may also occur in these structures, but not as a major Fe constituent. Our data suggest that this complex dendritic system in the beak is a common feature of birds, and that it may form an essential sensory basis for the evolution of at least certain types of magnetic field guided behavior.

Highlights

Unlike most plants, which are fixed to the substrate in which they grow, animals are generally motile
Following the histological procedures described in detail for homing pigeons [20,32], we detected identical iron-mineral containing structures in the inner dermal lining of the upper beak (Figure 1) of the four avian species: homing pigeons (Figure 1A), garden warblers (Figure 1B), European robins (Figure 1C), and domestic chickens (Figure 1D)
In the newly investigated bird species, garden warbler, European robin and domestic chicken, the Prussian Blue (PB) positive dendrites occur in several distinct areas near the lateral margin of the beak resembling the known pigeon micro-architecture

Summary

Introduction

Unlike most plants, which are fixed to the substrate in which they grow, animals are generally motile. They must move through their daily and seasonally changing environment in order to find, for example, food, sexual partners or nest sites. For this free moving life style, animals must have evolved navigational systems that enable them to identify where they are, how to reach a distant goal, and how to return to a previously visited location. The magnetic sense must be addressed as an additional and stand-alone sense, besides vision, hearing, olfaction, taste, electroreception and mechanosensation

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