Behavioral titration of a magnetic map coordinate.

Spatial variation in the inclination of the geomagnetic field has been implicated in the map component of homing by eastern red-spotted newts Notophthalmus viridescens. Here we show that when newts are exposed to small changes in magnetic inclination, the most dramatic effects on homing orientation occur at values close to the 'home value', as predicted by the magnetic map hypothesis (Phillips 1996). Newts reverse the direction of homing orientation over a range of inclination of 0.5 degrees spanning the home value, providing further evidence that magnetic inclination or one of its components (i.e., vertical or horizontal intensity) is used to derive map information.