Does the geomagnetic field intensity affect the flight path of homing pigeons?

Analysis of GPS recorded tracks of intact trigeminal sectioned pigeons.

Conditioning studies have shown that the ophthalmic branch of the trigeminal nerve is functionally involved in the perception of the geomagnetic field intensity. However, homing experiments conducted in the field with homing pigeons demonstrated that trigeminal mediation of magnetoreception is neither necessary nor sufficient for navigation from unfamiliar distant locations.

Nevertheless, the magnetic landscape and, in particular, local magnetic anomalies – as other topographical features (rivers, roads, mountains, coastlines) – might locally affect the flight path of pigeons during homing, producing deviations from the home direction. This could explain the results of some studies reporting the tendency of homing pigeons to fly either parallel or perpendicular to the magnetic isoclines.

In order to test this hypothesis we have conducted a series of releases with intact pigeons and birds subjected to section of the ophthalmic branch of the trigeminal nerve, whose tracks were recorded with GPS data loggers. If the local geomagnetic intensity affects the orientation of the birds, we should be able to detect a difference in the flight path orientation of the trigeminal sectioned and intact pigeons. Therefore, we have undertaken an analysis of the deviation from both the direction of the local geomagnetic gradient and the home direction at the release sites. Moreover, we have correlated the deviation of the flight path of each bird from the direction of the local magnetic gradient, with the deviation from the home direction “en route”, expecting that a significant correlation would be more likely in the intact group in comparison with the trigeminal sectioned group. Our results indicate that the flight path orientation both at the release site and “en route” is affected neither by the local geomagnetic field nor trigeminal nerve section.

A De Santis¹, C Filanino², P Ioalè², E and Qamili¹, M Savini², M Wild³, A. Gagliardo^2 1Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma, Italy, ²University of Pisa,, ³University of Auckland, New Zealand.