Land and Water

 

Here I want to add some more remarks on the interesting biology of the Chocoan River Turtle. We've published a number of articles on the species now, so I am also including links to articles in case someone wants to read more.

It has not been that difficult to find turtles on Isla Palma. We have estimated the population density of the turtles in the streams at between 1500-2400 individuals per hectare of water (600-970/acre), which is extremely dense (Giraldo et al. 2012, Garcés-Restrepo et al. 2014). We find it simplest to collect them at night by hand when they are most active, but it's not that unusual to find one swimming by day, or active around dusk. We've seen them eating plant leaves, flowers, and fruits that fall in the water. Most of their relatives seem to primarily be herbivores, but we have detected insects and fish in their feces, and have seen them eating dead fish and opossums, including finding one eating a dead water opossum on land (Carr et al. 2010)! Most similarly aquatic turtles cannot eat when out of the water because they do not have the salivary glands to facilitate swallowing, but the Chocoan River Turtle does. So we know it is an omnivore and will eat many kinds of things, both in and out of the water, but we have yet to conclude a more rigorous, quantitative diet study.

 

Other clues about the extent of this species forays onto land come in the area of reproduction. Mating behavior by aquatic turtles usually occurs in the water, but the Chocoan River Turtle has been seen mating both in shallow water and on shore near the water (Carr & Giraldo 2009, Carr et al. 2012). Egg laying of the single egg clutches are laid on land as is typical of aquatic turtles, but the egg is so large they cannot deposit it in an ordinary flask-shaped cavity they dig with the hind legs (Giraldo et al. 2013). Based on the one nest we've found and what happens in related turtles, apparently the female will dig a shallow pit in which to lay the egg, possibly not able to completely cover it afterwards. We have no idea how long this process may take, or how long a female may search for a suitable egg-laying site. A typical freshwater turtle female may spend 1-3 hours on land to nest, but we suspect much longer for the Chocoan River Turtle, perhaps days or weeks. Another possible clue to this comes from their ectoparasites. Typical relationships among turtle hosts and their parasites would be finding ticks on terrestrial turtles and leeches on aquatic turtles. Isla Palma has no leeches, but the Chocoan River Turtle has ticks (Garcés-Restrepo et al. 2013). Rather than this indicating something unusual about ticks adopting aquatic habits on the island, it may be an indicator of the extent of terrestrial activity by the aquatic turtles. In particular, we have recorded a higher incidence of ticks on adult females-perhaps a hint that they spend more time on land, presumably in egg laying activities.

Given these intriguing aspects of their natural history, biologging the wet-dry balance in the life of the Chocoan River Turtle could help elucidate these behaviors.