The Yellow-Spotted Sideneck Turtle , Podocnemis unifilis, in the Wild and Captivity: Natural History – Part 2

Click: The Yellow-Spotted Sideneck Turtle , Podocnemis unifilis, in the Wild and Captivity: Natural History – Part 1, to read the first part of this article.

Diet

Adults are mainly herbivorous and subsist largely upon aquatic vegetation and fallen fruits, but will also consume insects, fish, carrion, snails and crayfish (the preferred diet of juveniles).

The yellow-spotted sideneck sometimes utilizes a feeding method known as neustophagia to filter particulate food matter from the water’s surface.  The turtle opens its jaws at the surface and rapidly pumps the throat, which has the effect of drawing in only the thin surface film.  A rapid snap of the jaw expels the ingested water and retains the organic matter.  Neustophagia enables a relatively large turtle to obtain significant nutrition from a food source that would be otherwise too small to exploit.

This and related turtles sometimes gather in large numbers below trees overhanging water when fruits ripen and fall (please see below).

Reproduction

The mating season varies throughout the range.  As in many aquatic turtles, males court females by stroking their heads with the claws of the forelegs.

Females often nest communally, digging nest holes in sand or, on occasion, in mats of floating vegetation.  Several clutches may be produced each season, with 6-52 (average 19) eggs being laid at once.  The hatchlings average 1.6 inches in length, and emerge after 60-75 days.

Encounters in the Field

While engaged in field work with green anacondas, I was fortunate to find myself in the Venezuelan llanos… prime habitat of the savanna sideneck turtle, Podocnemis vogli, a close relative of the yellow-spotted sideneck.  On one memorable occasion, I came upon thousands of these shy yet inquisitive turtles at a river oxbow, below a stand of fruit trees.

Droves appeared at the surface, briefly looked at the boat and dove, to be replaced by an equal number of turtles a few seconds later.  Upon entering the water, I was astonished to find that the entire pool was packed, top to bottom, with turtles…to move, I literally had to push my way through a nearly solid mass of shells.  Being in the center of so many frantically swimming turtles was quite unlike anything I had experienced, either before or since.

Notes on Related Turtles

Podocnemis erythrocephala

The red-headed sideneck turtle, P. erythrocephala, is a much sought after species that rarely if ever enters the pet trade anymore.  Unlike many turtles, males retain the brilliant red head markings that characterize hatchlings.  Limited to the Rio Negro and Rio Casiquiare drainages in Venezuela and Brazil, it is a secretive species that mainly keeps to blackwater areas.

This turtle’s wild status has not been well-studied, but it is assumed threatened by past over-collection and habitat loss.  Those I have worked with proved to be fairly shy, even after nearly 3 decades in captivity. They did not rush towards me at feeding time, as would almost any other turtle after such a time period, and reproduced only sporadically.  We certainly need to learn more about the keys to the captive breeding of this species.

Podocnemis expansa

The giant South American river turtle (P. expansa) is the heavyweight of the family and, at 3 feet in length, one of the world’s largest freshwater turtles.  Inhabiting tributaries of the upper Amazon and rivers in the Caribbean drainages of Guyana and Venezuela, it favors deep water.  Females have the unfortunate habit of gathering in huge numbers along favored nesting sites at predictable times each year.  This renders both they and their eggs quite easy to collect, and the species is now in dire trouble throughout much of its range.

During my years at the Bronx Zoo, I cared for a breeding group of these impressive turtles, some of which approached 40 years as captives, and were likely 60-70 years old.  Several times I was called to Kennedy Airport to identify turtle eggs found in luggage (and, in one case, filling 2 shopping bags!).  Twice I was tempted to identify seized eggs as belonging to a sea turtle, but upon close examination and some research into the collection site found them rather to be eggs of this massive species.

A great deal of information concerning the harvesting and conservation of this and other South American turtles and tortoises is posted at:

http://www.fao.org/docrep/T0750E/t0750e09.htm

Image referenced from Wikipedia.