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Background Spontaneous magnetic alignment (SMA), in which animals position their body axis in fixed alignments relative to magnetic field lines, has been shown in several classes of vertebrates and invertebrates. Although these responses appear to be widespread, the functional significance and sensory mechanism(s) underlying SMA remain unclear. An intriguing example comes from observations of wild red foxes (Vulpes vulpes) that show a ~fourfold increase in hunting success when predatory ‘mousing’ attacks are directed toward magnetic north-northeast. This form of SMA is proposed to receive input from a photoreceptor-based magnetoreception mechanism perceived as a ‘visual pattern’ and used as a targeting system to increase the accuracy of mousing attempts targeting hidden prey. However, similar to previous observational studies of magnetic orientation in vertebrates, direct evidence for the use of magnetic cues, and field-based experiments designed to characterize the biophysical mechanisms of SMA are lacking. Here, we develop a new approach for studies of SMA using triaxial accelerometer and magnetometer bio-loggers attached to semidomesticated red foxes. Results Accelerometer data were recorded from 415 ground-truth events of three behaviors exhibited by an adult red fox. A 5-nearest neighbor classifier was developed for behavioral analysis and performed with an accuracy of 95.7% across all three behaviors. To evaluate the generalizability of the classifier, data from a second fox were tested yielding an accuracy of 66.7%, suggesting the classifier can extract behaviors across multiple foxes. A similar classification approach was used to identify the fox’s magnetic alignment using two 8-way classifiers with differing underlying assumptions to distinguish magnetic headings in eight equally spaced 45° sectors. The magnetic heading classifiers performed with 90.0 and 74.2% accuracy, suggesting a realistic performance range for a classifier based on an independent set of training events equal in size to our sample. Conclusions We report the development of ‘magnetic ethograms’ in which the behavior and magnetic alignment of foxes can be accurately extracted from raw sensor data. These techniques provide the basis for future studies of SMA where direct observation is not necessary and may allow for more sophisticated experimental designs aimed to characterize the sensory mechanisms mediating SMA behavior. Published version false (Extension publication?)

In dieser Studie werden die Sinnessysteme des Rotfuchses behandelt, im Speziellen der Hörsinn, der visuelle Sinn sowie der Magnetsinn. Im ersten Kapitel präsentiere ich ein Verhaltensaudiogramm dreier Rotfüchse. Der Hörbereich des Rotfuchses umfasst 9,84 Oktaven und erstreckt sich von 51 Hz bis 48 kHz. Die absolute Sensitivität (-15 dB SPL bei 4 kHz) ist außergewöhnlich und übertrifft sogar jene der Katze. Ergänzend beschreibe ich die Morphologie des auditorischen Systems des Rotfuchses. Die Beschreibung umfasst die funktionell relevanten Parameter des Außen-, Mittel- und Innenohrs, wie z. B. Abmessungen und Gewichte der Gehörknöchelchen, Flächen der akustischen Membranen, Haarzelldichten sowie die Feinmorphologie der Cochlea. Anschließend zeige ich, dass sich die Sensitivität des auditorischen Systems gut in der Morphologie widerspiegelt und es nur aufgrund der morphologischen Parameter möglich ist, eine recht genaue Vorhersage des Audiogramms zu erstellen. Im zweiten Kapitel stelle ich morphologische Aspekte des visuellen Systems des Rotfuchses vor. Mithilfe von Nissl-Färbungen und Immunhistochemie kartiere ich die retinalen Ganglienzellen und Fotorezeptoren für kurz- (S) und langwelliges (M/L) Licht auf der Retina des Fuchses. Auf dieser Basis berechne ich die Sehschärfe auf 6,3 Zyklen/Grad und die Schalllokalisierungsfähigkeit auf 3-4 Grad, beides innerhalb der Bandbreite anderer Karnivoren liegend. Selbiges gilt für die Verteilung der Zapfen, wobei die M/L-Zapfen einen zentroperipher abfallenden Dichtegradienten aufweisen und die S-Zapfen entlang eines dorsoventralen Gradienten an Dichte zunehmen. Das dritte Kapitel behandelt den Magnetsinn. Für Rotfüchse wurde ein Magnetsinn postuliert, welcher ihnen womöglich bei der Jagd auf Kleinnager zunutze sein könnte. Da der Fuchs beim Jagen hauptsächlich akustische Reize benutzt, wurde ein Einfluss magnetischer Felder auf den Hörsinn hypothetisiert. Aufgrund dessen habe ich die Hörschwelle von Rotfüchsen unter verschiedenen magnetischen Bedingungen getestet, jedoch keinen Hinweis auf einen Einfluss gefunden, weshalb die Hypothese als widerlegt gelten kann. Allerdings konnte ich histologische Befunde sammeln, die für eine Alternativhypothese sprechen, die ein visuell-magnetisches System, analog wie es bei Vögeln vermutet wird, zur Annahme hat: Beim Rotfuchs befindet sich das potentielle Magnetsensormolekül der Vögel, Cryptochrom 1, in den S-Zapfen der Retina. Im abschließenden Teil des letzten Kapitels präsentiere ich die Ergebnisse von Nestbauexperimenten mit Waldmäusen, welche das Vorhandensein eines Magnetsinnes bei diesen Tieren demonstrieren. Weiterhin scheint dieser Magnetsinn durch sehr schwache Radiofrequenzfelder beeinflussbar zu sein – ein Charakteristikum des Radikalpaar-Mechanismus der Magnetwahrnehmung. Dies ist der erste starke Hinweis für das Vorkommen eines derartigen Systems bei einem Säugetier. This study deals with the sensory systems of the red fox, more specifically with audition, vision, and magnetoreception. In the first chapter, I present the behavioural audiograms of three red fox specimens obtained by psychoacoustic procedures. The hearing range of the red fox covers 9.84 octaves ranging from 51 Hz to 48 kHz. The absolute sensitivity (-15 dB SPL at 4 kHz) of the red fox auditory sense is extraordinary, even exceeding that of the domestic cat. Complementary, I describe in detail the morphology of the red fox auditory system, including functionally relevant parameters of the outer, middle and inner ear, such as ossicle measurements and weight, acoustic membrane areas, sensory hair cell densities, and cochlear fine morphology. Subsequently, I demonstrate that the hearing sensitivity of the red fox is well reflected in the measurements and can be predicted with good accuracy on the morphological basis alone. The second chapter is a treatise of some morphological aspects of the visual system of the red fox. By means of Nissl staining and immunohistochemistry, I map the distribution of retinal ganglion cells and short (S) as well as long (M/L) wavelength photoreceptors over the fox retina. Based on the retinal ganglion cell maps the visual acuity of the red fox is assumedly 6.3 cy-cles/degree and the sound localization ability within the range of 3-4 degrees, thus, within the range of other carnivores. The same holds true for the cone distribution, with a centroperipheral decreasing gradient of M/L cones and a dorsoventral increasing density of S cones. The third chapter deals with the sense of magnetoreception. Foxes have been postulated to be magnetosensitive as that might help them during capture of small rodents. As prey capture is mainly auditorily guided, one hypothesis states an influence of magnetic fields on hearing sensitivity. Therefore, I determine the auditory sensitivity of red foxes in different magnetic fields and show that no influence I detectable, making the hypothesis unlikely. However, I show histological evidence in support of an alternative hypothesis which assumes a visual-magnetic system aiding prey capture, similar to the magnetosensitive system in birds: Red foxes, but not rodents, possess the potential magnetosensor of birds, cryptochrome 1 in the S cones of their retina. As an additional part of this chapter I present the results of nest building experiments with wood mice that demonstrates the existence of a magnetic sense and furthermore suggests sensitivity to very weak radiofrequency fields, characteristic for a radical-pair based system of magnetoreception. This is the first strong evidence for such a system in mammals. Dissertation, Universität Duisburg-Essen, 2014

Introduction: Several mammalian species spontaneously align their body axis with respect to the Earth's magnetic field (MF) lines in diverse behavioral contexts. Magnetic alignment is a suitable paradigm to scan for the occurrence of magnetosensitivity across animal taxa with the heuristic potential to contribute to the understanding of the mechanism of magnetoreception and identify further functions of magnetosensation apart from navigation. With this in mind we searched for signs of magnetic alignment in dogs. We measured the direction of the body axis in 70 dogs of 37 breeds during defecation (1,893 observations) and urination (5,582 observations) over a two-year period. After complete sampling, we sorted the data according to the geomagnetic conditions prevailing during the respective sampling periods. Relative declination and intensity changes of the MF during the respective dog walks were calculated from daily magnetograms. Directional preferences of dogs under different MF conditions were analyzed and tested by means of circular statistics.Results: Dogs preferred to excrete with the body being aligned along the North-South axis under calm MF conditions. This directional behavior was abolished under unstable MF. The best predictor of the behavioral switch was the rate of change in declination, i.e., polar orientation of the MF.Conclusions: It is for the first time that (a) magnetic sensitivity was proved in dogs, (b) a measurable, predictable behavioral reaction upon natural MF fluctuations could be unambiguously proven in a mammal, and (c) high sensitivity to small changes in polarity, rather than in intensity, of MF was identified as biologically meaningful. Our findings open new horizons in magnetoreception research. Since the MF is calm in only about 20% of the daylight period, our findings might provide an explanation why many magnetoreception experiments were hardly replicable and why directional values of records in diverse observations are frequently compromised by scatter. © 2013 Hart et al.; licensee BioMed Central Ltd. OA Förderung 2013