Moonlight and the Migratory Orientation of Savannah Sparrows (Passerculus sandwichensis)

Authors

  • Frank R. Moore

    Corresponding author
    1. Department of Biological Sciences, University of Southern Mississippi, Hattiesburg
      Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406-5018, USA.
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Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406-5018, USA.

Abstract

Migratory birds might respond to moonlight in at least four ways: (1) a geographical reference for selecting a compass direction, (2) a celestial ‘landmark’ to facilitate maintenance of a preferred heading, (3) a stimulus that distracts migrants and introduces error in compass orientation, or (4) a source of illumination that facilitates nocturnal flight. This study examines the response of migratory savannah sparrows (Passerculus sandwichensis) to moonlight during controlled tests in orientation cages. I found no evidence that savannah sparrows use a lunar compass to select a direction. If savannah sparrows do use the moon as a ‘landmark’ to maintain a direction selected with reference to a different cue, I expected birds to be better oriented on overcast nights when the moon is present than they are when the moon is absent. The results suggest otherwise. Usually, savannah sparrows respond phototactically to the moon by directing their cage activity toward or at a constant angle with respect to the moon's azimuth. Interestingly, the migrant's response to moonlight depended on whether the bird viewed the setting sun earlier that evening.

Ancillary