Frogs Take Up Residence In Manmade Caves In Portugal

frogSerra de Estrela Natural Park encompasses a section of Portugal’s highest mountains. The largest natural conservation area in that country, the park is full of wildlife. There are wall lizards, otters, wild cats, water moles, and even wolves, to name a few species.

Back in the 1950s, before the park’s boundaries were delineated, several artificial caves were created in the area. These were drainage galleries — small, horizontal tunnels built to push a few meters into the hillsides, often with a small stream of water running through.

In May 2010, according to a study from Portuguese researchers published in the Journal of Subterranean Biology, an unexpected resident was found in the galleries: the Iberian brown frog (Rana iberica). These frogs are often found the the mountains, and also live in other moist habitats, such as ponds and soaked fields and humid meadows. But they’d never been found in caves.

The researchers returned to the galleries the next year, every three months at first, then every month from December 2011 to December 2012. Adult frogs were found throughout the year, in day and in night, on the ground, tucked into crevices, swimming in water, and even climbing up the walls (as in the photo). Usually the frogs were living deeper into the galleries, more than five meters from the entrance where the daylight had dimmed.

The frogs mated throughout the year, then laid their eggs within the caves. The tadpoles hatched there, and the frogs grew up there. It wasn’t necessarily an easy life, however. Tadpoles would sometimes eat frog eggs — a first for this species — and tadpoles themselves were occasionally eaten by fire salamander larvae.

This may be just be a case of a species moving into a newly available habitat, but it might instead be a consequence of changes humans have made to the frogs’ home. “Nearby breeding sites may have disappeared or experienced disturbance,” the scientists hypothesize in their paper. But they also note that this region of the world is expected to experience dramatic climate change in the near future, with changes that include increasing aridity and greater fire activity. By taking up residence underground, the frogs may be smartly fleeing the changing landscape above. It could be a hopeful sign that the world’s wildlife will do its best to survive the changes we are making to their planet.

Image courtesy of Gonçalo M. Rosa, via EurekAlert

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