Ring-billed Gull (Larus delawarensis) chicks between the ages of 2 and 20 days were used in 680 orientation-cage trials. All of the experimental birds were taken from a population at Rogers City, Michigan. The apparently innate ability of chicks to select a southeasterly heading, the appropriate bearing for reaching their winter range, was compared when trials were conducted under various intensities of magnetic disturbance (0 to 7K which equals disturbances of 0 to 200 gamma). During minor disturbances (0-3K) a statistically significant proportion of the experimental birds selected southeasterly headings but during higher intensity ’storms’ (4-7K) there was a breakdown in such preferences and no statistically significant mean direction was present for the data. Evidence to date suggests that the mode of orientation used by young Ring-billed gulls for selecting the direction of fall migration is altered by fluctuations in the earth’s magnetic field.