Pondhenge? Giant Frogs Move and Arrange Giant Rocks in Cameroon


It’s often said that frogs and toads are the canaries in the giant coal mine known as Earth and their mysterious diseases and disappearances are a cause for alarm. Here’s a sign that the frogs themselves may be getting ready for an amphibi-gegdon themselves. Frog researchers in Cameroon have found endangered giant Goliath frogs moving stones over half their size to their ponds and arranging them. Is this a sign we’re all going to (here it comes) croak?

“The fact that we’ve only just discovered these behaviours shows how little we know about even some of the most spectacular creatures on our planet.”

“Spectacular” is a good word for describing the Goliath frog (Conraua Goliath), the largest living frog on Earth. Dr. Mark-Oliver Rödel, author of a new study in the Journal of Natural History and the president of Frogs & Friends in Berlin, led a team to West Cameroon – one of only two places (Equatorial Guinea is the other) where the “spectacular” Goliath frogs still live. The creatures an reach 13 inches (33 cm) in length from snout to vent and weigh up to 7.2 lb. (3.25 kg). At that size, it’s not surprising that they’re a primary food source for snakes, Nile crocodiles, Nile monitors and local humans. Their current status as an endangered species is due to hunting, habitat loss to development and the global pet trade. It’s no wonder these giants are dragging stones weighing up to 4.4 pounds (2 kg) and arranging them. But why?

There’s more to frogs than just lily pads

“Goliath frogs are not only huge, but our discovery shows they seem to be attentive parents as well. The little ponds they make at the edges of fast-flowing rivers provide their eggs and tadpoles with a safe haven from sometimes torrential waters, as well as from the many predators living there.”

Study co-author Marvin Schäfer from the Berlin Natural History Museum said in a press release that the Goliath frogs are also threatened by their very lifeblood—the rivers where they live and raise their young. Because the currents are so fast and the rivers are full of predators, it appears these giants are hauling huge stones to the edge of the rivers to make small, calm and protected ponds where they can safely lay their eggs and allow them to reach maturity. While it was known that Goliath frogs make “nests” for their eggs, the way they created these artificial ponds had never been determined … until Rödel and Schäfer set up camera traps for time-lapse photography.

Dams are most obvious in the third type, for which frogs clear depressions of shallow water of any large stones, moving them to edge and creating circular pond. This was the most reliable type, as eggs were least likely to spill out or become over-flooded after heavy rain. Infrared time-lapse revealed an adult spending all night guarding a nest from predators, only ending the vigil just before dawn. The scientists were unable to determine which sex was responsible for building ponds or which for guarding them, although one hunter who described the behaviours in detail suggested that males do the construction while females are the guards.”

So, the giant frogs move giant stones into a circular structure which makes them feel safe when they’re inside of it, provides them with a place for fertility rituals and is used to bring peace and harmony to their lives and those of their offspring. Does that sound like Stonehenge to anyone else?

The study makes a few interesting speculations. The stone nests themselves tend to appear in clusters, which may indicate that the Goliath frogs are territorial. It could also be that the female doesn’t deposit all of her eggs in one stone basket, forcing her Goliath mate to build multiple stone ponds. Finally, they theorize that moving these massive stones to build the nests has actually contributed to or caused the giantism its known for.

“Digging out a nest that exceeds 1 m in diameter and 10 cm in depth, by moving coarse gravel and stones of several kilograms, is a serious physical task, and suggest a potential explanation for why Goliath frogs are among the largest frogs in the world.”

The typical reaction to frog extinction

Will these Goliath frogs be able to build their Pondhenges fast enough to stave off extinction? The government of Equatorial Guinea has placed restrictions on exporting them, but they must also stop the destruction of Dicraeia warmingii (Podostemaceae), a plant found only near waterfalls and rapids which is the only thing their tadpoles eat until they grow big enough to down dragonflies, crabs, turtles , spiders, snakes and an occasional low-flying bat.

Maybe it would help if they held frog festivals on the equinoxes.

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