has yet been able to give the slightest indication of what the magnetic-sensitive organs are, nor whether they have sufficient acuity for us to be able to speak of a menotaxis, let alone orientation. By contrast, the bird’s eye is a very highly developed sense organ. Recent work suggests that European robins do not even detect north from the polarity of the magnetic field but from its angle to the horizon (43).Hypotheses that the earth magnetic field could provide a navigational grid date as far back as the work Viguier completed in 1882. The outcome of his work suggested that birds could detect and measure three components of the field, its intensity, inclination (the angle which a compass needle makes with the horizontal) and declination (the angle between magnetic and geographical north). These three components vary more or less with independence of one another so that their isolines would form a complex grid. Over the next few years, several different scientists restated this hypothesis, with minor variations. The complete lack of evidence for any direct reaction to a magnetic field in birds is a very questionable issue (Carthy 46). Can birds actually use magnetic stimuli as an internal compass? Well Casamajor (1927) and Wodzicki (1939) found that fixing magnets to the head of the Pigeon and the Stork, had no effect on their homing ability. There are many other theoretical difficulties that may provide an answer as to why the magnets did not affect the homing ability of the two animals in question (48). An important one is that measurement of declination requires an exact knowledge of geographical north. Elimination of the declination isolines from the magnetic grid reduces the plausibility of the whole scheme, since the inclination and intensity isolines generally cross one another at oblique angles making good ‘fixes’ impossible (Lincoln 79).With these initial theoretical difficulties in mind the conc...
