Sea-Finding Behaviour of Loggerhead Hatchlings: The Time Course of Transient Circling Following Unilateral and Asynchronous Bilateral Blindfolding

Abstract

Marine turtle hatchlings orient seaward by responding to photic cues that guide them toward the brightest horizon. Earlier research has suggested that they have a positive phototropotactic reaction to light but the behaviour must be more complex than this because circling both toward the uncovered and the covered eye has been observed in unilaterally blindfolded turtles. The present work resolved some of these problems by studying circling direction as a function of how long one eye had been covered prior to testing. Different groups of neonate loggerhead turtles (Caretta caretta) were tested from 10 s to 19 h after the application of a unilateral blindfold. The longer this had been on, the less the turtle circled, but beyond 1 h further changes were slight. Initially, circling was predominantly toward the uncovered eye but after the blindfold had been on for 1 h circling toward the covered eye occurred equally often.The time course of circling was also examined in asynchronously, bilaterally blind-folded turtles. One eye was covered 6 h before the other, and tests were made at various times after the second eye had been covered. Asynchronous bilateral blindfolding caused more intense circling and disrupted seaward orientation more severely than unilateral blindfolding. The time course of the decline in circling showed similarities between both treatments, suggesting that they were activating the same mechanism. Dark adaptation was examined as a possible explanation of such transient turning tendencies and previous models of sea-finding were elaborated.

How Turtles Find the Sea

“…A fairer indication of poor orientation is that so many turtles did not traverse the arena within the 2 min. Unblindfolded turtles tested in similar circumstances nearly always travel this distance in a much shorter time and nearly always without making any circles (KINGSMILL 1980). Fig.…”

Migration in amphibians and reptiles: An overview of patterns and orientation mechanisms in relation to life history strategies

“…First, upon emerging from the nests, hatchlings use visual cues to orient towards the sea. Studies have shown that hatchling Loggerhead and Green Turtles exhibit a strong phototropotactic response, and will orient towards the brightest light in the vicinity, which, in the absence of artificial lights, is the horizon over the ocean, highlighted by the reflection of light off the ocean (Carr 1962;Kingsmill and Mrosovsky 1982;Mrosovsky and Kingsmill 1985;Salmon and Wyneken 1990;Peters and Verhoeven 1994) (Fig. 7).…”