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An adult Giant South American river turtle. The turtle
is the largest member of the side-necked turtle family and
grows up to nearly three feet in length. Photo credit: C.
Ferrara/Wildlife Conservation Society
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Turtles are well known for their longevity and
protective shells, but it turns out these reptiles use sound to stick together
and care for young, according to the Wildlife Conservation Society and other
organizations.
Scientists working in the Brazilian Amazon have
found that Giant South American river turtles actually use several different
kinds of vocal communication to coordinate their social behaviors, including
one used by female turtles to call to their newly hatched offspring in what is
the first instance of recorded parental care in turtles.
"These distinctive sounds made by turtles give
us unique insights into their behavior, although we don't know what the sounds
mean," said Dr. Camila Ferrara, Aquatic Turtle Specialist for the WCS
Brazil Program. "The social behaviors of these reptiles are much more
complex than previously thought."
Some behaviors of the Giant South American river
turtle have been well known for some time, including the tendency to aggregate
in huge numbers during the nesting season. However, the mechanisms used by
turtles to coordinate their activities have yet to be explained. This study
focused on the sounds made by the turtles as a possible means of facilitating
social behavior.
Working on the Rio Trombetas between 2009 and 2011,
the research team captured 270 individual sounds made during 220 hours of
recording made with both microphones and hydrophones when the turtles were
swimming through the river. The scientists then conducted spectrographic
analyses on the repertoire, which they subdivided into six different types of
vocalization made by turtles during the nesting season, which begins as the
reptiles leave the seasonally flooded forest for nesting beaches along river
banks. The scientists also sought to correlate vocalizations with specific
behaviors.
Sounds made by the turtles while migrating through
the river or basking tended to be low frequency sounds, possibly to facilitate
contact between turtles over longer distances. Vocalizations made during
nesting tended to be higher frequency sounds, possibly because higher frequency
sounds travel better in shallow water and in the air.
The highest diversity of sounds are used by females
about to nest; the researchers theorize that the animals use these sounds to
decide on a specific nesting site and to synchronize their movements (the
turtles leave the water in a single-file procession).
The hatchling turtles themselves make sounds before
they hatch and continue to do so as they clamber out of the nest chamber on the
river beach. The sounds, the authors speculate, may stimulate group hatching.
The females, in turn, vocalize in response to the nestling calls, perhaps
guiding the nestlings into the water. These interactions -- the first recorded
instance of parental care in turtles -- were featured in a 2012 study appearing
in the Journal of Comparative Psychology.
Using sonic transmitters, the team also discovered
that the hatchlings remain together and migrate with adult females for more
than two months.
The Giant South American river turtle is the largest
of the side-necked turtle family and grows up to 80 centimeters (nearly three
feet) in length. The species is only found in the Amazon River basin and is now
threatened by unregulated consumption of the turtles' meat and eggs.
"Groundbreaking studies such as this one can
help us better understand the complex relationships between both individual
animals and their environment," said Dr. Julie Kunen, Executive Director
of WCS's Latin America and the Caribbean Program. "Protecting the still
sizable populations of Giant South American river turtles will also enable us
to conserve the behavioral richness of these reptiles for future study."
Research on the Giant South American river turtles
is part of a new long-term WCS conservation program called Amazon Waters, an
initiative focusing on the conservation of aquatic ecosystems and species.
Citation
Ferrara CR, Vogt RC, Sousa-Lima RS, Tardio BMR, Bernardes
VCD. 2014. Sound Communication and Social Behavior in an Amazonian River
Turtle (Podocnemis expansa). Herpetologica,
70:149 DOI: 10.1655/HERPETOLOGICA-D-13-00050R2