Bird Migration: The Magnetic Compass (3D)

This simulator renders Earth as a magnetic dipole in 3D, with real dipole field lines traced from the McIlwain L-shell equation and a migrating bird placed at any chosen latitude. The bird's sensed heading is computed from a simplified but physically grounded model of cryptochrome-based magnetoreception: it reads the field's inclination (dip) angle — an axial quantity insensitive to which way the field vector points — rather than following the vector like a compass needle. Drag the latitude slider or click the globe to relocate the bird, flip the field's polarity to see that a real inclination-compass bird stays on course while a naive polarity-following model does not, and dim or redden the light to watch the radical-pair signal (and the bird's orientation confidence) collapse, matching real behavioral experiments on caged migratory birds.