Magnetic Inclination Compass

Compass Model

Season

Sensor noise 6°

Flight speed 1.0×

Flock Telemetry

Avg. dip angle |I|

–°

Avg. heading error

–°

In magnetic-equator ambiguity zone

0 / 0

How it works

Earth's field behaves like a tilted bar magnet (a dipole). At magnetic latitude λ_m, the field's dip angle I above/below the horizontal follows the dipole law:

tan(I) = 2·tan(λ_m)
sin(λ_m) = poŝ · axiŝ   (unit position dotted with the magnetic-axis unit vector)

Migratory songbirds don't read compass polarity (N vs S) the way a hiker's compass does. Wiltschko & Wiltschko's classic experiments showed they instead sense the angle between the field vector and gravity — an inclination compass — and fly toward wherever that angle gets steeper (more acute), combined with their own sense of up/down.

Inclination (real) mode: each bird's heading is set by the local horizontal field direction, signed by the vertical component and gravity — exactly the axial mechanism found in real birds.
Polarity (hypothetical) mode: birds instead just follow the horizontal field vector like an ordinary compass needle, ignoring the vertical component — included only for comparison, this is not how birds actually navigate.
Reverse vertical (Z) field reproduces the Wiltschkos' key experiment: artificially flipping only the up/down field component reverses a real (inclination-compass) bird's migratory direction, while a polarity-compass bird would show no change — watch the two modes diverge.
Near the magnetic equator the dip angle passes through zero and the up/down cue vanishes, so real birds show measurable disorientation there — the flock visibly wanders in the shaded "ambiguity zone" readout.

This is a real, well-established mechanism (magnetoreception via the inclination compass) documented across many migratory bird species — not a claim about a universal "sixth sense," just one specific, measured sensory strategy.

Migrating flock Magnetic axis (N) Field lines

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