

A radio-tagged Scaphiophryne gottlebei individual from the Zahavola site. Photo by Gonçalo Rosa

Researchers have radio-tracked frogs for the first time in Madagascar.

The effort, undertaken by a group of European scientists, is detailed in the current issue of Herpetologica.

Attaching tiny radio transmitters weighing 0.3-0.35 grams (1/100 of an ounce) to 36 rainbow frogs (Scaphiophryne gottlebei), the research team tracked the movement of the colorful frogs through rugged canyons in Madagascar’s Isalo Massif. They found that the frogs have a short breeding period that occurs after the first intense rainfall at the start of the rainy season. The researchers also learned that the sexes behave similarly in terms of activity levels, and were able to confirm the preferred habitat of the species, which is listed as “Endangered” by the IUCN due to over-collection for the pet trade.

“Our data confirm that S. gottlebei is a secretive species, hiding in sand or in holes in the canyon walls,” the authors write. “Our observations also confirm that this species is active after the first heavy rains and displays rapid breeding activity, with adult individuals continuing their activity in the canyon. We did not note any territorial behavior, but the short distances covered during dispersion suggest a strong fidelity to their original locations.”



A radio-tagged Scaphiophryne gottlebei individual from the Zahavola site. Photo by Gonçalo Rosa

While teasing out behavioral patterns of the endangered frog is an achievement in its own right, more importantly the study demonstrated the effectiveness of using radio telemetry on small amphibians.

“This is the first documented application of radio telemetry on a Malagasy amphibian,” note the authors. Although radio-tracking has been done previously on amphibians in Europe, those studies relied on implanted transmitters, a procedure the authors say presents unnecessary risks in a remote part of southwestern Madagascar.

“We consider this [other] invasive technique difficult to apply when working in the field, hazardous where hygiene conditions are insufficient (and thus increases the animals’ susceptibility to septicemia), and inadequate when the species has a short breeding period like that of S. gottlebei.”

Study co-author Gonçalo M. Rosa told Mongabay.com that the approach seems to have a low impact on the frogs, which were monitored for several hours before being released back into the wild after being fitted with transmitters.

“According to available literature and previous studies, the recommended ratio is 5–10 percent of transmitter-to-body-mass, which we respected in our study,” he said. “While we cannot exclude the possibility that these external transmitters and antenna may affect the dispersion of the animals [they] do not seem to have compromised the results.”

“This is not a perfect technique but it provides valuable data to better understand the species ecology and contribute more efficiently to its conservation.”

Rosa went on to say that the study revealed predators of the species — three were eaten by snakes and four by mammals.

“As an amphibian, S. gottlebei is a great food source (at least during this breeding season when they aggregate in large numbers) for many species, particularly snakes. This device gave the chance to find out some new predators of the species and, on the other, some species that [take advantage of] these breeding aggregations.”

Overall 14 of the 36 tagged frogs died or disappeared during the study period. The background rate of mortality among adult rainbow frogs is unknown, but studies with other frog species have documented rates ranging from 8-60 percent for individuals during a single breeding season.

The researchers say they plan to apply the technique to other small wildlife species in Madagascar, including a type of lizard.

“Telemetry has mostly been done with large animals such as wolves, bears, and cats, but we are talking of its application to a 2 cm long animal,” said Rosa. “It gives a good picture of spatial ecology, movement and activity patterns of the tracked species. All this information helps to better understand not only the species ecology and natural history, but also provides useful knowledge that allows to establish more efficient conservation measures identifying, for example, key areas where we should focus our efforts.”

CITATION: Franco Andreone, Paolo Eusebio Bergo, Vincenzo Mercurio, and Goncalo M. Rosa. Spatial Ecology of Scaphiophryne Gottlebei in the Canyons of the Isalo Massif, Madagascar. Herpetologica, 69(1), 2013, 11–21

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