The Goliath frog is an impressive enough creature based on its size alone. As the name suggests, it is a hefty beast that can reach weights of 3.3 kilograms (7.3 pounds) and lengths greater than 34 centimeters (13.4 inches) not including the legs.
But now, scientists writing in the Journal of Natural History have discovered a new characteristic that is equally as enthralling – the frog builds ponds for its young. This is the first example of “nest-building" in an African amphibian. In fact, the researchers suspect it is this very behavior that has enabled them to grow to such a large size.
"Goliath frogs are not only huge, but our discovery shows they seem to be attentive parents as well," study author Marvin Schäfer, from the Berlin Natural History Museum, said in a statement. "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. We think that the heavy work they put into excavation and moving rocks may explain why gigantism evolved in these frogs in the first place."
Schäfer and colleagues discovered this curious habit using infrared time-lapse set up to watch the nest. They noted three nest types of differing complexities. The first involved a relatively simple job of clearing leaf-litter and debris from naturally occurring rock pools. These stood in stark contrast to the surrounding puddles that contain a layer of leaves, debris, and gravel.
The next required the frog to form a dam with the leaf litter and gravel by digging it up and pushing it to the edges. The third involved the frog clearing shallow water depressions of large stones up to 2 kilograms (4.4 pounds) in weight and moving them to form a dam around the pond’s edge. This method was the most effective at preventing overfill or flooding.
When the pond was built, a frog would stay guard and watch over their young at night to prevent any predators from getting too close. Their shift would end just before dawn.
"The fact that we've only just discovered these behaviors shows how little we know about even some of the most spectacular creatures on our planet," said Mark-Oliver Rödel, project leader and president of Frogs & Friends. "We hope that our findings, combined with further ongoing research, will improve our understanding of the needs of the Goliath frog so we can help support its continued survival."
Hopefully, it's not too late. The range of the Goliath frog is restricted to Cameroon and Equatorial Guinea and overhunting and deforestation have caused numbers to plummet 50 percent in just 10 years. They are categorized as endangered on the IUCN Red List.