Zebra finches have a light-dependent magnetic compass similar to migratory birds

Abstract

Birds have a light-dependent magnetic compass that provides information about the spatial alignment of the geomagnetic field. It is proposed to be located in the avian retina and mediated by a lightinduced, radical-pair mechanism involving cryptochromes as sensory receptor molecules. To investigate how the behavioural responses of birds under different light spectra match with cryptochromes as the primary magnetoreceptor, we examined the spectral properties of the magnetic compass in zebra finches. We trained birds to relocate a food reward in a spatial orientation task using magnetic compass cues. The birds were well oriented along the trained magnetic compass axis when trained and tested under low-irradiance 521 nm green light. In the presence of a 1.4 MHz radio-frequency electromagnetic (RF)-field, the birds were disoriented, which supports the involvement of radical-pair reactions in the primary magnetoreception process. Birds trained and tested under 638 nm red light showed a weak tendency to orient ∼45 deg clockwise of the trained magnetic direction. Under low-irradiance 460 nm blue light, they tended to orient along the trained magnetic compass axis, but were disoriented under higher irradiance light. Zebra finches trained and tested under high-irradiance 430 nm indigo light were well oriented along the trained magnetic compass axis, but disoriented in the presence of a RF-field. We conclude that magnetic compass responses of zebra finches are similar to those observed in nocturnally migrating birds and agree with cryptochromes as the primary magnetoreceptor, suggesting that light-dependent, radicalpair-mediated magnetoreception is a common property for all birds, including non-migratory species.

Expression patterns of cryptochrome genes in avian retina suggest involvement of Cry4 in light-dependent magnetoreception

“…Indeed, retinal Cry4 from birds has recently been shown to undergo structural changes in the carboxyl-terminal region in a light-dependent manner consistent with magnetic compass orientation in birds [27,28,56]. However, considering that a growing number of studies has shown that birds use their magnetic compass not only for orientation during migration, but also for short-distance spatial orientation task in their daily life [12,20,45,46], we argue that any magnetoreceptor should be expressed at equal levels irrespective of time of day and season, thus would not be expected to follow a circadian expression pattern. In conclusion, our data suggest that Cry4 is the most likely candidate for the magnetoreceptor of the avian light-dependent magnetic compass, and that Cry1 and Cry2 are part of the retinal circadian clock in zebra finches.…”

Searching for magnetic compass mechanism in pigeon retinal photoreceptors

“…A large body of behavioral data indicates that the avian magnetic compass has several important properties: it is based on the inclination angle of the magnetic field lines rather than on the polarity of the field [1], it is light-dependent, and, moreover, it depends on the light spectral composition. In experiments on magnetic compass orientation, birds of different species were able to orient under UV, blue and green light and disoriented under yellow and red light [3][4][5][6][7][8], for a review see 9]. Based on this fact, the primary magnetoreceptor in birds is supposed to be localized in the retina of the eye, and the prevalent hypothesis describing the work of such a magnetoreceptor is the radical pair model [10, 11; reviewed in 12].…”

Magnetoreception—A sense without a receptor

“…Fifthly, whether they rely on conditional or instinctive readouts, the establishment of behavioral paradigms that assess magnetoreception are notoriously difficult. Anything from nT strength RF interference to the chosen perfume of experimenters can render an assay useless [ 35 , 53 ]. Sixthly, there has been a major issue with independent replication in the field.…”