A conservation success story started with digging holes

Humans can go to extremes to try to save creatures from extinction. Drones and other devices track every movement of some animals. Generations of rare species are raised in captivity. Your sperm will be frozen and saved for future emergencies. Entire islands are being cleared of invasive species.

But sometimes it’s the simple things that help. Like digging holes in the ground and filling them with water.

This is what happened in the Swiss state of Aargau. In the 1990s, the region began constructing ponds to help their ailing amphibians. Now, after 20 years of data collection, scientists have returned with a verdict: it worked.

“Even though the negative reports about biodiversity loss can be overwhelming, our study shows that conservation measures are worthwhile and that populations can recover,” says Helen Moor, ecologist at the Swiss Federal Institute for Forest, Snow and Forest Landscape Research WSL. “Sooner or later, every newly created pond is valuable for amphibians.”

Amphibians could use some good news. More than 40% are threatened with extinction, the largest percentage of any plant or animal group, according to the International Union for the Conservation of Nature. As creatures that live in both water and land, they are vulnerable to the loss of a wide variety of habitats, whether it be drained wetlands, cleared forests, or paved migration routes. Their moist, permeable skin makes them particularly sensitive to chemical stress. Then there’s the deadly chytrid fungus that afflicts amphibians on multiple continents, driving some to extinction.

Switzerland’s Aargau region, a landscape of rolling fields, forests and small towns along Germany’s southern border, was no different in seeing a decline in amphibian numbers. What is different is that they decided to do something about it on a large scale. Beginning in 1991, they built more than 400 new ponds across the state, which covers 1,400 square kilometers, about half the size of Rhode Island.

While such a project makes intuitive sense — pond-loving frogs, toads, and newts would certainly increase with more ponds — efforts to restore species don’t always go as hoped. Thus, scientists traced the fate of 12 species of amphibians in 856 ponds, almost half of which were recently built.

Now, after counting frogs for more than two decades, scientists say the ponds appeared to offer significant benefits. Ten of the 12 species increased in number in the state while one remained stable over the period, according to a study published Monday in the Proceedings of the National Academy of Sciences.

“We were amazed at the clear result,” says Moor. “Especially given that the other threats haven’t diminished in the meantime.”

The scientists suspect there are a few reasons the additional ponds helped. More ponds mean more places for species to meet and lay eggs. The new ponds provided fresh space for some amphibians that prefer ponds with less vegetation. And the higher concentration of ponds made it easier to move from one pond to another, especially for species like newts that only travel a few hundred meters.

Not all amphibians benefited equally. Different frogs prefer different types of ponds. For example, the natterjack toad, named for the loud, rasping calls made by males during spring mating season, lives in large, shallow ponds that experience frequent dry spells. The lack of such ponds could explain why this is one of the dozen amphibians that have not fared well.

The pond program may need to continue to sustain this early success. The researchers found that as some species thrive in ponds with less vegetation, people will either have to keep building new ponds or “reset” existing ones.

However, the general message is that more ponds are better. “No effort in pond construction is really wasted,” the researchers write. “Some species will benefit from this.”

Or, to paraphrase Kevin Costner in the Bull Durham film, “Build it and they will come.”

Moor, et al. “Bending the Curve: Simple but massive preservation action leads to a landscape-scale recovery of amphibians.” Proceedings of the National Academy of Sciences. October 10, 2022.

Image: A pair of common toads (Bufo bufo) in the spring. © Christoph Vorburger and Benedikt Schmid