Free-ranging Manx shearwaters do not rely on magnetic maps or compasses

Many animals, from moths to sharks, are thought to navigate using the earth's magnetic field.^{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15} The field can provide both compass information and-through spatial variation in inclination, declination, and intensity-positional information.^16,17 Night-migratory songbirds are sensitive to the inclination of the earth's magnetic field, using this cue as a compass^5,18 and perhaps as part of a map sense.^13,14,15 However, without a definitively identified receptor,^{18,19,20,21,22,23,24,25} and with mixed evidence from experiments in other birds,^{26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46} avian magnetoreception remains controversial. Following recent observational findings that wild Manx shearwaters (Puffinus puffinus) use geomagnetic inclination to relocate their natal colony after their first migration,⁴⁷ we used this species to conduct the largest magnetic disruption experiment in wild birds to date. We found no effects of magnetic disruption on movement or navigation during the long-distance foraging trips of adult Manx shearwaters. Assessment of effect sizes and confidence intervals suggests that shearwaters do not require geomagnetic cues to home accurately. This demonstrates that at least some birds are capable of remarkable long-distance navigation in the absence of geomagnetic information, and we propose that the field of animal navigation should seek to understand the factors driving the differences in the navigational mechanisms of avian taxa.