Orientation of migratory birds under ultraviolet light.

In view of the finding that cryptochrome 1a, the putative receptor molecule for the avian magnetic compass, is restricted to the ultraviolet single cones in European Robins, we studied the orientation behaviour of robins and Australian Silvereyes under monochromatic ultraviolet (UV) light. At low intensity UV light of 0.3 mW/m(2), birds showed normal migratory orientation by their inclination compass, with the directional information originating in radical pair processes in the eye. At 2.8 mW/m(2), robins showed an axial preference in the east-west axis, whereas silvereyes preferred an easterly direction. At 5.7 mW/m(2), robins changed direction to a north-south axis. When UV light was combined with yellow light, robins showed easterly 'fixed direction' responses, which changed to disorientation when their upper beak was locally anaesthetised with xylocaine, indicating that they were controlled by the magnetite-based receptors in the beak. Orientation under UV light thus appears to be similar to that observed under blue, turquoise and green light, albeit the UV responses occur at lower light levels, probably because of the greater light sensitivity of the UV cones. The orientation under UV light and green light suggests that at least at the level of the retina, magnetoreception and vision are largely independent of each other.

Conditioning domestic chickens to a magnetic anomaly.

Young domestic chicks of two strains, ISA brown layers and White Leghorn X Australorps, were trained to associate a magnetic anomaly with food. This was done by feeding them in their housing boxes from a dish placed above a small coil that produced a magnetic anomaly roughly six times as strong as the local geomagnetic field. Unrewarded tests began on day 9 after hatching. In a square arena, two corresponding coils were placed underneath two opposite corners. One coil, the control coil, was double-wrapped producing no net magnetic field, while the other in the opposite corner produced a local magnetic anomaly similar to that experienced during feeding. The chicks favoured the corner with the anomaly from day 10 after hatching onward. Both strains of chickens showed this preference, indicating that they could sense the local changes in the magnetic field.

Avian orientation: the pulse effect is mediated by the magnetite receptors in the upper beak.

Migratory silvereyes treated with a strong magnetic pulse shift their headings by approximately 90 degrees , indicating an involvement of magnetite-based receptors in the orientation process. Structures containing superparamagnetic magnetite have been described in the inner skin at the edges of the upper beak of birds, while single-domain magnetite particles are indicated in the nasal cavity. To test which of these structures mediate the pulse effect, we subjected migratory silvereyes, Zosterops l. lateralis, to a strong pulse, and then tested their orientation, while the skin of their upper beak was anaesthetized with a local anaesthetic to temporarily deactivate the magnetite-containing structures there. After the pulse, birds without anaesthesia showed the typical shift, whereas when their beak was anaesthetized, they maintained their original headings. This indicates that the superparamagnetic magnetite-containing structures in the skin of the upper beak are most likely the magnetoreceptors that cause the change in headings observed after pulse treatment.

Light-dependent magnetoreception: orientation behaviour of migratory birds under dim red light.

Magnetic compass orientation in migratory birds has been shown to be based on radical pair processes and to require light from the short wavelength part of the spectrum up to 565 nm Green. Under dim red light of 645 nm wavelength and 1 mW m(-2) intensity, Australian silvereyes and European robins showed a westerly tendency that did not change between spring and autumn, identifying it as a 'fixed direction' response. A thorough analysis revealed that this orientation did not involve the inclination compass, but was a response based on the polarity of the magnetic field. Furthermore, in contrast to the orientation under short-wavelength light, it could be disrupted by local anaesthesia of the upper beak where iron-containing receptors are located, indicating that it is controlled by these receptors. The similarity of the response under dim red light to the response in total darkness suggests that the two responses may be identical. These findings indicate that the observed 'fixed direction' response under dim red light is fundamentally different from the normal compass orientation, which is based on radical pair processes.

Different responses in two strains of chickens (Gallus gallus) in a magnetic orientation test.

Previous studies demonstrated that layer strain domestic chicks bred for egg production can orient using directional cues from the magnetic field; here we report that chicks from a broiler strain bred for meat production do not use magnetic cues for orientation. We imprinted both strains of chicken on a red ball and subsequently trained them in a featureless testing arena. Between rewarded trials in the geomagnetic field, we inserted unrewarded tests under the following conditions: (1) in the geomagnetic field, (2) in a magnetic field with North shifted by 90 degrees and (3) in a magnetic field with the inclination inverted. The layer chicks made a correct axial response in 75-80% of the tests, shifting their choices following a rotation of magnetic North. Chicks of the broiler strain, in contrast, performed at chance level with between 47 and 60% of choices on the correct axis. This difference between the strains does not appear to be due to substantial strain differences in motivation to perform the task. It therefore appears possible that the selection of the broiler strain has led to the elimination of the specific ability to respond to magnetic cues in the test situation.

Gorillas are a host for Dientamoeba fragilis: an update on the life cycle and host distribution.

Dientamoeba fragilis is a gastrointestinal protozoan that has a worldwide distribution and is emergeing as a common cause of diarrhea. As D. fragilis has a propensity to cause chronic illness with symptoms similar to irritable bowel syndrome (IBS) it is not surprising that some patients with D. fragilis are misdiagnosed as having IBS. In contrast to most other pathogenic protozoa very little is known about its life cycle, epidemiology and mode of transmission. What role animal reservoirs play in the transmission of this parasite is unknown. Consequently we undertook a prospective study to determine the host distribution of D. fragilis. Over a 2-year-period, 608 faecal samples from a wide range of animal and bird species, including pigs and other food species, were screened using permanent stained smears for the presence of D. fragilis. Trophozoites of D. fragilis were only detected in Western lowland gorillas (3/10) (Gorilla g. gorilla) and confirmed by PCR targeting the SSU rRNA gene. The limited host range detected suggests human infection may not involve transmission from other animal species. In addition, we provide an update on the limited knowledge about the life cycle of this parasite and its host distribution.

Lateralized response of chicks to magnetic cues.

Previous research has shown that the ability to orient with the use of directional cues from the geomagnetic field is lateralized in three avian species: orientation is possible when the birds are restricted to use of their right eye, but not when they have to use their left eye. This has been interpreted as possible lateralization of the perception mechanisms for magnetic cues in favour of the right eye. Recent discovery of magnetic compass orientation in domestic chicks, a species in which lateralization has been well studied, has made available a model system in which to explore these lateralized processes more fully. Hence we tested chicks monocularly in the same test conditions as used previously to demonstrate the chick's use of a magnetic compass. In a magnetic field with North shifted by 90 degrees , chicks using their right eye oriented according to magnetic cues, whereas chicks using the left eye did not, but continued to prefer the original direction. Analysis of the times taken to respond indicated longer latencies in the chicks using their left eye, suggesting a possible conflict between cues. The different behaviour of the chicks using their left eye might not be a matter of a right eye-left hemisphere specialization for detecting magnetic directions, but of hemispheric specialization for attending to specific types of cues.

The magnetic compass of domestic chickens, Gallus gallus.

By directional training, young domestic chickens have been shown to use a magnetic compass; the same method has now been used to analyse the functional characteristics and the physical principles underlying the chickens' magnetic compass. Tests in magnetic fields with different intensities revealed a functional window around the intensity of the local geomagnetic field, with this window extending further towards lower than higher intensities. Testing chickens under monochromatic 465 nm blue and 645 nm red light suggested a wavelength dependence, with orientation possible under blue but not under red light. Exposing chickens to an oscillating field of 1.566 MHz led to disorientation, identifying an underlying radical pair mechanism. Local anesthesia of the upper beak, where iron-rich structures have been described as potential magnetoreceptors, did not affect the performance, suggesting that these receptors are not involved in compass orientation. These findings show obvious parallels to the magnetic compass described for European robins, indicating that chickens and small passerines use the same type of magnetic compass mechanism. This suggests that the avian magnetic compass may have evolved in the common ancestor of all present-day birds to facilitate orientation within the home range.

Magnetite-based magnetoreception: the effect of repeated pulsing on the orientation of migratory birds.

Previous studies have shown that a magnetic pulse affected the orientation of passerine migrants for a short period only: for about 3 days, the birds' headings were deflected eastward from their migratory direction, followed by a phase of disorientation, with the birds returning to their normal migratory direction after about 10 days. To analyze the processes involved in the fading of the pulse effect, migratory birds were subjected to a second, identical pulse 16 days after the first pulse, when the effect of that pulse had disappeared. This second pulse affected the birds' behavior in a different way: it caused an increase in the scatter of the birds' headings for 2 days, after which the birds showed normal migratory orientation again. These observations are at variance with the hypothesis that the magnetite-based receptor had been fully restored, but also with the hypothesis that the input of this receptor was ignored. They rather indicate dynamic processes, which include changes in the affected receptor, but at the same time cause the birds to weigh and rate the altered input differently. The bearing of these findings on the question of whether single domains or superparamagnetic particles are involved in the magnetite-based receptors is discussed.

Bird navigation: what type of information does the magnetite-based receptor provide?

Previous experiments have shown that a short, strong magnetic pulse caused migratory birds to change their headings from their normal migratory direction to an easterly direction in both spring and autumn. In order to analyse the nature of this pulse effect, we subjected migratory Australian silvereyes, Zosterops lateralis, to a magnetic pulse and tested their subsequent response under different magnetic conditions. In the local geomagnetic field, the birds preferred easterly headings as before, and when the horizontal component of the magnetic field was shifted 90 degrees anticlockwise, they altered their headings accordingly northwards. In a field with the vertical component inverted, the birds reversed their headings to westwards, indicating that their directional orientation was controlled by the normal inclination compass. These findings show that although the pulse strongly affects the magnetite particles, it leaves the functional mechanism of the magnetic compass intact. Thus, magnetite-based receptors seem to mediate magnetic 'map'-information used to determine position, and when affected by a pulse, they provide birds with false positional information that causes them to change their course.

Magnetic orientation in birds: non-compass responses under monochromatic light of increased intensity.

Migratory Australian silvereyes (Zosterops lateralis) were tested under monochromatic light at wavelengths of 424 nm blue and 565 nm green. At a low light level of 7 x 10(15) quanta m(-2) s(-1) in the local geomagnetic field, the birds preferred their seasonally appropriate southern migratory direction under both wavelengths. Their reversal of headings when the vertical component of the magnetic field was inverted indicated normal use of the avian inclination compass. A higher light intensity of 43 x 10(15) quanta m(-2) s(-1), however, caused a fundamental change in behaviour: under bright blue, the silvereyes showed an axial tendency along the east-west axis; under bright green, they showed a unimodal preference of a west-northwesterly direction that followed a shift in magnetic north, but was not reversed by inverting the vertical component of the magnetic field. Hence it is not based on the inclination compass. The change in behaviour at higher light intensities suggests a complex interaction between at least two receptors. The polar nature of the response under bright green cannot be explained by the current models of light-dependent magnetoreception and will lead to new considerations on these receptive processes.

Magnetite-based magnetoreception in birds: the effect of a biasing field and a pulse on migratory behavior.

To test the hypothesis that single domain magnetite is involved in magnetoreception, we treated Australian silvereyes Zosterops l. lateralis with a strong, brief pulse designed to alter the magnetization of single domain particles. This pulse was administered in the presence of a 1 mT biasing field, either parallel to the direction of the biasing field (PAR group) or antiparallel (ANTI group). In the case of magnetoreceptors based on freely moving single domain particles, the PAR treatment should have little effect, whereas the ANTI treatment should cause remagnetization of the magnetite particles involved in a receptor and could produce a maximum change in that receptor's output for some receptor configurations. Migratory orientation was used as a criterion to assess the effect on the receptor. Before treatment, both groups preferred their normal northerly migratory direction. Exposure to the biasing field alone did not affect their behavior. Treatment with the pulse in the presence of the biasing field caused both the PAR and the ANTI birds to show an axial preference for the east-west axis, with no difference between the two groups. Although these results are in accordance with magnetite-based magnetoreceptors playing a role in migratory orientation, they do not support the hypothesis that single domains in polarity-sensitive receptors are free to move through all solid angles. Possible interpretations, including other arrangements of single domains and superparamagnetic crystals, are discussed.