Conservation: Frog numbers explode after massive pond excavation

Switzerland has reversed the decline of more than half of endangered frogs, toads and newts in an area, research has found.

After conservationists dug hundreds of new ponds in the canton of Aargau, the number of amphibians increased significantly.

European tree frog populations in particular "exploded", scientists say.

Scientists hope that this method can be used globally because pond construction is simple and effective.

Factors including habitat loss, urbanization, road infrastructure, disease and invasive species have led to significant declines in amphibian populations globally.

In 1999 the Aargau decided that a massive conservation effort was needed to tackle the loss of the amphibians. Of particular concern was the fall of the European tree frog.

This frog prefers to jump from bushes to trees, explains Dr. Moore, and is one of the most mobile species, capable of traveling several kilometres.

It requires a very specific habitat to thrive, preferring shallow ponds created by flowing rivers over floodplains.

But this type of habitat has disappeared in many places in Switzerland, leading to a decline in the species.

Dr Moore points out that Switzerland, like Britain, has a high population density with a large road and railway network, and most of the non-urban land is cultivated.

"Habitat loss is one of the main problems, and only by addressing it can we see the difference it makes, and begin the recovery of these species," she says.

The regional population of the European tree frog has quadrupled in an area in 20 years. In 1999 it could only be found at 16 sites in Reusstal but as of 2019 the species was living in 77 sites.

The massive territorial increase in nearly every pond-breeding amphibian species the study shows proves just how successful habitat construction can be.

"The main message is that it pays to do something, even if it feels overwhelming," Dr. Moore said.

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The ponds will continue to be monitored and the species will be ensured to flourish.

Some ponds will need to be cleared of vegetation and removed to remove predatory larvae that pose a threat to tadpoles.

Dr Moore hopes this conservation success will convince other landowners to build ponds and diversify habitats.

This research is published in the Proceedings of the National Academy of Sciences.

State officials, non-profit organizations, private landowners and hundreds of volunteers worked for 20 years to build 422 ponds in five areas in Aargau.

Lack of space, overpopulation of predators and dense vegetation made the old ponds unsuitable for some amphibians.

By creating new ponds, conservationists gave the species more room to thrive.

Of the eight endangered species, 52% increased their regional populations and 32% stabilized.

Dr Helen Moore, lead author of the study, told BBC News she was excited to see "such a marked increase" in numbers given the simplicity of the solution.

"Species will come, they will settle down and start using the space if you offer it to them," she said.

One of the species that grew dramatically was the small European tree frog.