1. Endogenous Programs and the Development of Sea Finding
Orientation of Loggerhead Hatchlings (Caretta caretta L.).
Christie A. Barrett1, 2
Michael Salmon2
1
Coastal Planning and Engineering, Inc.
2481 NW Boca Raton Boulevard
Boca Raton, Florida, USA
2
Department of Biological Sciences
Florida Atlantic University
Boca Raton, Florida, USA
Abstract
Previous experiments have shown that newly emerged loggerhead hatchlings
(Caretta caretta L) transfer a crawling vector to their magnetic compass, used later to
swim offshore. Our objective was to determine if that transfer was expedited by crawling
for a specific time period – one that corresponded to the typical duration of a crawl from
the nest to the surf zone. Support for that hypothesis would suggest that hatchlings
possessed an “endogenous program” that optimized vector transfer when the turtles
crawled for an “appropriate” time. To find out, we measured how far nests were placed
from the surf zone, then measured hatchling crawling speed. We then did experiments to
determine whether vector transfer occurred more readily after turtles had crawled in the
lab for different time periods.
On average, hatchlings crawled to the ocean in less than 4 min. In the lab, 1 and 5
min crawls did not result in vector transfer whereas those of 2 min did. A period of non-
directional crawling interfered with the ability of a 2 min crawl to promote calibration.
These results suggest that transfer of a crawling vector to the turtles’ magnetic compass
occurs most readily when crawls are directional, and last on average about as long as a
natural crawl. These results suggest that hatchlings possess an endogenous program for
vector transfer, apparently shaped by where their mothers place nests on the beach.

2. Introduction
In this study, we reveal the importance of an endogenous timing program in the transfer
of a crawling vector maintained by a visual compass, to a swimming vector maintained
by a magnetic compass in hatchling loggerhead sea turtles (Caretta caretta L.). Our
goals were to 1) determine how long, on average, hatchlings crawl to reach the ocean
from their nest, 2) whether the efficiency of vector transfer is related to a “typical”
duration of crawling, and 3) to determine if it is the time spent crawling, or the time spent
in oriented crawling, that is most important for vector transfer.
Methods
Nest Location and Crawling Time: The distances between 10 consecutively placed
nests and the surf zone was measured at high tide on seven beaches (three nourished
beaches and four natural sites). The three nourished nesting beaches were North
Hillsboro, Red Reef Park, and Spanish River Park. The four natural beaches were
Waveland, Normandy, Melbourne, and Juno Beach.
Crawling times were recorded at two adjacent, nourished beach sites in Pompano Beach,
Florida. A transect was established so that the landward end began at the nests which
were ready to emerge during that night’s experiment. Each transect extended eastward 15
m toward the ocean and were subdivided into five 3 m lengths, using small wooden sticks
as markers. As each turtle crawled, it was followed from behind by an observer.
Observers carried a stopwatch and recorded the elapsed time taken by the turtle to
complete each 3 m portion of its 15 m crawl.
Laboratory Experiments- Hatchlings: Turtles were obtained from a hatchery in
Hillsboro Beach, Palm Beach Co. (26˚ 15’ 56.34 N x 80˚ 4’ 47.34 W) between May –
September, 2003. Captured turtles were placed on a shallow layer of moist sand inside of
a light-tight Styrofoam® box and transported to my laboratory about 10 km distant, at
Florida Atlantic University (Boca Raton). Experiments were completed later that night
within 2-4 h. At the end of each night’s experiments, hatchlings were transported to a
nearby beach and released.
Crawling and Swimming Arenas: Experiments were done in two steps. Hatchlings
were initially tethered inside an empty circular plastic arena where they completed a
crawl (Fig. 1). The arena contained a dim light placed to the east. If that light was turned
on, hatchlings crawled toward the light. If the light was turned off, their crawl lacked
direction. After the crawl, the turtles swam under complete darkness inside a water-filled
pool (second step; Fig. 2). An encoder signaled the arm’s horizontal position to a
computer. “Arena Tracker”, a software program designed by W. P. Irwin (University of
North Carolina, Chapel Hill), stored the turtle’s heading every 10 s and calculated a mean
angle of orientation for each turtle’s 30 min swimming trial. Vector transfer occurred if
the turtles swam in the same direction (east) that they had crawled.

3. Experiments and Treatments: We conducted two experiments. In the first experiment,
turtles were divided into three treatment groups that crawled toward the light for 2, 5, or
10 min, respectively. In the second experiment, turtles were divided into four treatment
groups. Groups I and II crawled toward an east light for 1 and 2 min, respectively. The
turtles in Groups III and IV initially crawled in total darkness for 3 and 8 min,
respectively. The light was then turned on for two min, inducing each turtle to crawl
east. Thus, total crawling time for turtles in Groups III and IV was 5 and 10 min,
respectively, but oriented crawling was confined to the last two minutes of their trial.
Statistical Analysis: A Kolmogorov-Smirnov normality test (Dytham 1999) was used to
confirm that nest distances and crawl times were normally distributed. A two-tailed t-test
for unequal sample sizes to determine if there were significant differences (at p < 0.05)
between nest distances at the nourished and non-nourished beach sites. A one-way
ANOVA to determine if the time to crawl each distance differed significantly (at p <
0.05) between the two Pompano Beach sites. A General Linear Regression was used to
determine if crawling time and distance were significantly related (at p < 0.05), and to
estimate if crawling speed increased, decreased, or remained the same with distance.
The mean angle for each swimming turtle was used to calculate a second-order
group mean angle and r-vector (dispersion) for the turtles in each treatment group. We
used a Rayleigh test (Zar 1999) to determine at the end of each evening if any group
showed significant orientation (at p = 0.05) in the biologically appropriate direction
(east). When a group achieved significant orientation in the appropriate direction and
maintained significance in this direction, we concluded that the crawling treatment
experienced by that group promoted vector transfer more rapidly than the other crawling
treatments.
Results
Nest Location: Nests were located significantly farther from the ocean at high tide at
natural (mean + sd = 13.3 + 2.6 m; range = 7.6 – 18.5 m; n = 40 nests) than at nourished
(9.5 + 3.9 m; range = 2.9 – 16.2 m; n = 30 nests) beaches (t68 = 4.76, p = 0.001).
Crawling Time: Crawling times were normally distributed (KS test p ranged between
0.252 and 0.967). There were no significant differences in the time to crawl 3, 6, 9, 12,
or 15 m at the two sites. Crawling time was significantly related to distance and showed
a linear relationship (p < 0.001). The observed average crawling speed over 15 m was
3.22 m/min.
Vector Transfer: In the first experiment, the hatchlings that crawled toward the light for
2 min were the first group to show significant orientation while swimming (Rayleigh z =
4.8, p < 0.01; Fig.3). Turtles that crawled toward the light for 5 or 10 min failed to
achieve significant group orientation at a same sample size of 20. In the second
experiment, the 2 min group was the first treatment to achieve significant group

4. orientation in the appropriate direction (Rayleigh z = 3.3, p < 0.04, Fig. 4). A sample
size of 28 turtles was required to achieve the criterion. Neither group of turtles that
initially crawled in the dark before light exposure achieved significant group orientation
while swimming.
Discussion and Conclusions
• Loggerhead nests were located father from the surf zone at natural than at
nourished beaches. Similar observations were made in a study comparing nest
placement at nourished and natural sections of the same beach at Hutchinson
Island, Florida (Ernest & Martin 1999). Thus, hatchlings must crawl further to
reach the ocean on natural beaches than they do nourished beaches.
• Our data on nest position and crawling speed (3.22 m/min) can be used to
estimate how long hatchlings will crawl to reach the sea. On nourished beaches,
it should take hatchlings between 0.9 and 5.0 min to crawl to the sea, whereas on
natural beaches it should take between 2.4 and 5.7 min. However, Dial (1987)
measured a crawling speed (6.5 m/min) that was twice as fast as the one
calculated in this study. If Dial’s crawling speed is used with my nest
measurement distances, crawling time to the ocean ranges between 0.45 and 2.49
min on nourished beaches, and between 1.17 to 2.85 min on natural beaches.
Given both results hatchlings probably complete their crawl in under 5 min.
• Turtles either increased their crawling speed and/or crawled more directly
seaward as they negotiated the 15 m distance.
• Crawls that are too short (1 min) or too long (>5 min) are not as effective as a 2
min crawl at calibration. In addition, this study also demonstrated that crawl
direction is important since a Prior period of non-directional crawling interfered
with the ability of a 2 min directional crawl to promote calibration.
• Hatchlings emerge from the nest with endogenous programs that specify they
should crawl in 1 direction (offshore) for a period of time (2 min) that roughly
matches the time it takes to reach the ocean from the nest. This timing program is
probably one of several that control when hatchlings switch from one compass to
another.
Acknowlegdments
Financial and logistical support was given by the Florida Atlantic University Center For
Sea Turtle Research and Coastal Planning & Engineering, Inc.. We would like to thank
the following individuals for their generous contributions to this research: A. Guidry, W.
Irwin, K. Purdy, C. Makowski, A. Marsh, A. Nash, M. Sagristano, J. Wetterer and J.
Wyneken.
References
Dial, B.E. 1987. Energetics and performance during nest emergence and the hatchlings
frenzy in loggerhead sea turtles (Caretta caretta). Herpetologica, 43(3), 307-315.

5. Dytham, C. 1999. Choosing and Using Statistics. Malden: Blackwell Science.
Ernest, R.G. & Martin, R.E. 1999. Martin County beach renourishment project: sea turtle
monitoring and studies, 1997 annual report and final assessment. Ecological
Associates, Inc., http://edocs.dlis.state.fl.us/fldocs/dep/beaches/sea-turtles.pdf
Irwin, William P. 2004. Magnetic compass orientation and magnetoreception in
hatchling loggerhead sea turtles. Ph. D. Dissertation, University of North
Carolina.
Zar, J. H. 1999. Biostatistical Analysis. New Jersey: Prentice Hall.