Iron-mineral-based magnetoreception in birds: the stimulus conducting system

Birds are among the most throughly investigated model systems for the analysis of the impact of magnetic fields on behavior and physiology. They are known to be able to use astonishingly small changes in field intensity, direction and inclination between locations as a magnetic map and compass. However, the neurobiological mechanisms and the magnetophysical principles of the underlying sensory processes that lead to this ability are largely unknown. For many years these organisms have been treated as black box systems with magnetic field components as input and various behavioral phenomena as output. Many hypotheses that do not incorporate neurobiological principles or magnetophysical background knowledge have been derived based on the results of such studies. In this study, for the first time, we make use of physiological receptor paradigms in order to obtain a sound model for iron-mineral-based magnetoreception in birds. Based on histological and physicochemical data from a dendritic system in the avian beak, we present a model of the stimulus conducting system that recognizes the adequate stimulus. Special receptor features transform this stimulus into peripheral nervous system excitation, and the local magnetic field vector is then perceived via information processing performed by the central nervous system. Based on this approach, further neurobiological and behavioral experiments can be developed that critically test the proposed model of magnetoreception and, in particular, study the complex processes of perception and motor control that occur during magnetic field orientation in more depth.