Investigating the impact of weak geomagnetic fluctuations on pigeon races.

The existence of avian magnetic orientation has been proved by many experimental studies, however, evidence for the use of magnetic cues by homing pigeons remains controversial. To investigate magnetic orientation by homing pigeons, we analyzed the results of pigeon races relative to weak fluctuations in the geomagnetic field, assuming that such disturbances could impact navigational efficiency if based on magnetoreception. Whereas most of the previous studies recorded and analyzed vanishing bearing of individually released pigeons, we evaluated relative duration of the homeward flight (homing speed, as a proxy of navigational efficiency) and its dependence on specific geomagnetic indices in racing pigeons released collectively. Our analysis of orientation efficiency of about 289 pigeon races over 15 years suggested slight negative correlations between geomagnetic fluctuations and homing time. Although the interpretation of this finding is manifold and not clear, it suggests that natural magnetic variations or disturbances can affect the homing orientation performance of pigeons. We suggest that studying pigeon races may have a heuristic potential and since these races are regularly and frequently organized in many countries all over the globe, examining homing performance relative to a suite of environmental variables may be useful for exploring hypotheses about pigeon navigation.

Magnetic sorbents biomineralization on the basis of iron sulphides.

Biomineralization means mineral formation under the influence of organisms. Sulphate-reducing bacteria (SRB) constitute an essential role of iron sulphide minerals precipitation. Their composition involves amorphous, non-stoichiometric or crystalline iron sulphides, weakly or strongly magnetic. Variation in environmental conditions can alter the reactive iron species within the mineral, potentially modifying their magnetic properties. Biogenic iron sulphide minerals can be used as heavy metals and toxic ions adsorbents in soil or water remediation. For these reasons, a series of laboratory-scale iron sulphide synthesis experiments with the aim to study the chemical composition, mineralogy and magnetic properties of iron sulphide precipitates were carried out using SRB under various cultivation mode and nutrient medium composition. Energy-dispersive X-ray analysis (EDX) showed formation of iron sulphides in all biogenic samples and iron phosphates in abiotic controls. Results of X-ray diffraction analysis (XRD) in biomineralized samples confirmed nanocrystalline greigite, mackinawite and sulphur alpha. Magnetic measurements showed that sample prepared by static cultivation without addition of fresh nutrient medium was the most magnetic, magnetic hysteresis of sample formed under semicontinuous mode without any nutrient supply was the lowest. Abiotic samples contained only vivianite and they did not prove any significant response to magnetic field.

Magnetically induced behaviour of ferritin corpuscles in avian ears: can cuticulosomes function as magnetosomes?

Magnetoreception is an enigmatic, poorly understood sensory ability, described mainly on the basis of behavioural studies in animals of diverse taxa. Recently, corpuscles containing superparamagnetic iron-storage protein ferritin were found in the inner ear hair cells of birds, a predominantly single ferritin corpuscle per cell. It was suggested that these corpuscles might represent magnetosomes and function as magnetosensors. Here we determine ferritin low-field paramagnetic susceptibility to estimate its magnetically induced intracellular behaviour. Physical simulations show that ferritin corpuscles cannot be deformed or rotate in weak geomagnetic fields, and thus cannot provide magnetoreception via deformation of the cuticular plate. Furthermore, we reached an alternative hypothesis that ferritin corpuscle in avian ears may function as an intracellular electromagnetic oscillator. Such an oscillator would generate additional cellular electric potential related to normal cell conditions. Though the phenomenon seems to be weak, this effect deserves further analyses.

Iron-based granules in body of bumblebees.

The paper deals with the presence of iron-based granules in body parts of bumblebees. Two groups of bumblebees were collected from their natural habitat, industrial landscape, and from a breeding station. Detection of the magnetic particles was performed by a vibratory magnetometer and their morphology and elemental composition was analysed by scanning electron microscopy with EDX microanalysis. By means of the EDX spectra, wild bumblebees were found to have many magnetic and non-magnetic particles on their body, containing Fe, O, Al, Si, Bi, Mg, K, and Ni, likely having origin in the industrial pollution of the environment. In the case of bred bumblebees the presence of iron-rich granules, which occurred more abundantly in subsurface tissues on the head and wings, was observed. Phase analysis based on X-ray diffraction shows that iron-based granules contain magnetite and wuestite and Mössbauer spectroscopy admits a superparamagnetic form of these minerals. Magnetoreception, i.e. the sensory function of these granules, is discussed within the paper.

Hypothetical superparamagnetic magnetometer in a pigeon's upper beak probably does not work.

We reanalysed the role of superparamagnetic magnetite clusters observed in a pigeon's upper beak to decide if this matter can be a component of some sort of pigeon magnetometer for Earth orientation. We investigated the mutual interaction of the magnetite clusters induced by the geomagnetic field. The force sensitivity of the hypothetical magnetometer in a pigeon's upper beak was estimated considering the previously presented threshold magnetic sensitivity of pigeons, measured in electrophysiological and behavioural investigations. The typical intercluster magnetic force seems to be 10(-19)N well above the threshold magnetic sensitivity. To strengthen our results, we measured the magnetic susceptibility of superparamagnetic magnetite using a vibrating sample magnetometer. Finally we performed theoretical kinematic analysis of the motion of magnetite clusters in cell plasma. The results indicate that magnetite clusters, constituted by superparamagnetic nanoparticles and observed in a pigeon's upper beak, may not be a component of a measuring system providing the magnetic map.