First published online October 27, 2003
Use of multiple orientation cues by juvenile loggerhead sea turtles Caretta caretta
Larisa Avens1,2,* and
Kenneth J. Lohmann1
1 Department of Biology, University of North Carolina, Chapel Hill, North
Carolina 27599-3280, USA
2 National Oceanic and Atmospheric Administration, Beaufort Laboratory,
National Marine Fisheries Service, Beaufort, North Carolina 28516,
USA
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Fig. 1. Diagram of the experimental arena and the data acquisition system used to
monitor the orientation of juvenile loggerhead sea turtles (not to scale).
Each turtle was fitted with a Nylon–Lycra harness and tethered to a
freely rotating arm in the center of the arena. Data were acquired by a
computer located approximately 5 m to the south of the arena. See text for
details of testing procedure.
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Fig. 2. Magnet and brass bar attachment to loggerhead turtles. Felt pads were
attached to the dorsal surface of the head and the anterior margin of the
carapace; magnets or brass bars sewn into felt pouches were attached to the
felt pads. See text for details.
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Fig. 3. Juvenile loggerhead turtle fitted with goggles containing frosted lenses.
The goggle frames were attached to the turtle using cyanoacrylate adhesive and
fit snugly to the contours of the turtle's head, so that turtles were unable
to view the sky or surroundings.
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Fig. 4. Representative orientations of three juvenile loggerhead turtles tethered
in the experimental arena. Each turtle is denoted by a different symbol. Time
is indicated along the horizontal axis and the angle of orientation is
indicated along the vertical axis. Each dotted line represents the mean
heading of the turtle over its 10 min trial. Once a turtle established a
course, it typically maintained relatively consistent headings for the
duration of the trial.
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Fig. 5. Results of magnetic impairment experiment. Each dot represents the angular
difference between an individual turtle's mean heading on Day 2
versus Day 1. All four groups of turtles oriented in the expected
direction of 0°. (A) No treatment; mean angle=11°, r=0.50,
P<0.005 V-test, 95% confidence interval ±49°; (B) Brass
bars; mean angle=26°, r=0.35, P<0.01 V-test, 95%
confidence interval ±90°; (C) North-up magnets; mean angle=12°,
r=0.46, P<0.025 V-test, 95% confidence interval
±56°; (D) South-up magnets; mean angle=357°, r=0.34,
P<0.025 V-test, 95% confidence interval ±90°. See text
for statistical comparison of distributions.
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Fig. 6. Results of visual impairment experiment. Each dot represents the angular
difference between an individual turtle's mean heading on Day 2
versus Day 1. Loggerheads in all three treatment groups maintained
similar headings on Day 1 and Day 2. (A) No treatment; mean angle=356°,
r=0.61, P<0.01 V-test, 95% confidence interval
±51°; (B) Goggles with no lenses; mean angle=9°, r=0.58,
P<0.01 V-test, 95% confidence interval ±51°; (C)
Goggles containing frosted lenses; mean angle=335°, r=0.60,
P<0.01 V-test, 95% confidence interval ±48°. The
expected direction in all cases was 0°. See text for statistical
comparison of distributions.
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Fig. 7. Results of combined magnetic and visual impairment experiment. Each dot
represents the angular difference between an individual turtle's mean heading
on Day 2 versus Day 1. Turtles wearing frosted goggles and fitted
with brass bars maintained an orientation direction from Day 1 to Day 2, while
those bearing frosted goggles and magnets did not do so. (A) Brass bars +
frosted goggles; mean angle=31°, r=0.69, P<0.01 V-test,
95% confidence interval ±41°; (B) South-up magnets + frosted
goggles; mean angle=196°, r=0.65, NS V-test; (C) North-up magnets +
frosted goggles; mean angle=110°, r=0.37, NS V-test. See text for
statistical comparison of distributions. NS, not significant.
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© The Company of Biologists Ltd 2003
