European robin (Copyright: iStock)
Micro-SXRF Fe-maps of dendritic areas in four avian species. (Credit: G. Falkenberg et al.)
- new study of iron containing sensory dendrites
A team of scientists from HASYLAB/DESY, University of Oldenburg, and Helmholtz-Zentrum Berlin led by Frankfurt University researchers, discovered that iron containing sensory dendrites in the inner dermal lining of the upper beak are a candidate structure for an avian magnetometer system of birds. The physicochemical studies were performed at DORIS III. Previously published results, obtained by scientists of this team, offered an deeper insight into the iron-containing structures in the beaks of homing pigeons.
In this new study the scientists showed that similar structures occur in two species of migratory birds (e.g. the European robin ('Rotkehlchen'), see photo) and a non-migratory bird, the domestic chicken. In all these different bird species, histological data have revealed dendrites of similar shape and size. They are all containing iron minerals within distinct subcellular compartments of nervous terminals of the median branch of the Nervus ophthalmicus.
By using microscopic X-ray absorption spectroscopy the scientists found the composition of the involved iron minerals in the dendrits to be identical in all samples. The authors assume, that this complex dendritic system in the beak is a common feature of birds. It may form an essential sensory basis for the evolution of at least certain types of magnetic field guided behavior, provided that such a sense would be sensitive to minuscule changes in magnetic field intensity and inclination.
The figure on the right shows only Fe-maps. Areas with iron containing dendrites are selected for micro-SXRF maps in different bird species (A) garden warbler, (B) European robin, (C) domestic chicken, (D) homing pigeon. (10 µm sections mounted on Ultralene foil). (figure no. in paper: doi:10.1371/journal.pone.0009231.g004).
Since the orientation and navigation behavior of the investigated bird species are very different, the results may be surprising. A magnetic map is important at all the different navigation scales. Not only short to long-distance migrants but also resident birds need to find their way over long or short distances.
(...from paper and authors)
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