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Artificial Lighting and Seafinding by Loggerhead Hatchlings: Evidence for Lunar Modulation

Michael Salmon and Blair E. Witherington
Copeia
Vol. 1995, No. 4 (Dec. 21, 1995), pp. 931-938
DOI: 10.2307/1447042
Stable URL: http://www.jstor.org/stable/1447042
Page Count: 8
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Artificial Lighting and Seafinding by Loggerhead Hatchlings: Evidence for Lunar Modulation
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Abstract

Hatchling sea turtles generally emerge from nests at night and crawl immediately toward the ocean ("seafinding orientation"). On natural, dark beaches their orientation is usually appropriate, but where oceanfront buildings are present, hatchlings may crawl toward artificial lighting behind the beach. A systematic survey during the 1993 nesting season documented that, on Florida's beaches, such abnormal behavior ("disrupted orientation") occurred most often on dark nights around new moon and least often under full-moon illumination. Experiments on an urbanized Florida beach (Boca Raton, Palm Beach County) showed that background illumination from the moon, and not an attraction to the moon itself, restored normal seafinding orientation. Background illumination reduced, but did not eliminate, light intensity gradients imposed by artificial lighting. Thus, when seafinding was restored, hatchlings moved toward dimmer, not brighter, horizons. These results suggest that loggerhead hatchlings can locate the sea using mechanisms other than a positive phototaxis (the most widely held view). An alternative hypothesis, supported by these results, is that hatchlings locate the ocean by crawling away from objects behind the beach (dune, vegetation, or buildings) using shape and/or elevation cues.

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