To study if homing pigeons can discriminate between the presence and absence of a magnetic anomaly in a conditioned choice experiment.
Two conflicting hypotheses compete to explain how a homing pigeon can return to its loft over great distances: One proposes the use of atmospheric odours and the other the use of geomagnetic field.
The pigeons were conditioned to jump onto a platform at one end of the cage when the anomaly was present and onto an identical platform at the other end of the cage when the anomaly was absent.; correct answers were rewarded with food whereas incorrect choices were punished with a time penalty. Two female and two male experienced racing pigeons were studied.
Different impairment experiments were performed (e.g. attachment of a magnet to the cere, local anaesthesia of the upper beak area, and bilateral section of the ophthalmic branch of the trigeminal nerve or of the olfactory nerve).
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| Additional info | Four individual trained pigeons were required to discriminate the presence or absence of an induced magnetic field anomaly while freely walking in a wooden tunnel. The birds were conditioned to jump onto a platform at one end of the tunnel or to an identical platform at the other end depending on the presence or absent of field. The correct choices were rewarded with food while the incorrect choices were punished with a time penalty. |
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| Chamber | Wooden tunnel (3.3 m long x 1.06 m wide x 0.96 m high) with two identical platforms (48 cm high) located at the opposite ends. Each platform was fitted with micro-switches to detect the pigeon and a rotating feeder disc for accessing food. Two transparent curtains were suspended from the ceiling of the tunnel forced the pigeon to walk and not fly between the platforms. The coils were located above and below the center of the tunnel. |
| Additional info | During the control experiment, five 6.8 ohm resistors were wired parallel to match the effect of the coils load on the power source. Successful discrimination of the MF anomaly permitted a series of impairment experiments. In the first series of experiments, a small but strong rare earth magnets (NdFeB cylinders of 3 mm diameter and 2 mm in length with a field strength of 2500 µT at 1 cm) were attached to the cere. The orientation of the magnet was either south-up or north-up for two groups each consisting of 2 pigeons. Control session were carried out by replacing magnets with brass weights. In the second series of experiments, the olfactory cavity (upper beak area) was locally anesthetized using a 2% lignocaine hydrochloride solution. In the third series of experiments bilateral sectioning of the ophthalmic branch of trigeminal nerve was performed. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 44 µT | minimum | unspecified | - | inclination of -64° |
| magnetic flux density | 189 µT | maximum | unspecified | - | inclination of -80° |
The data demonstrate that homing pigeons can discriminate between the presence and absence of a magnetic anomaly. This discrimination is impaired by attachment of a magnet to the cere, local anaesthesia of the upper beak area, and bilateral section of the ophthalmic branch of the trigeminal nerve, but not of the olfactory nerve.
These results indicate that magnetoreception (probably magnetite-based) occurs in the upper beak area of the pigeon.
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