Sooglossidae frogs

Seychelles is home to a very unusual endemic family of frogs called Sooglossids. The family

Seychelles sooglossid © Gideon Climo

Sooglossidae consists of 2 genera and 4 species of frogs found only on the granitic islands of the Seychelles. The Seychelles granitic islands are unique among oceanic islands in representing a fragment of continental Gondwanaland. The Seychelles microcontinent split from India isolating the ancestral Sooglossidae at least 75 million years ago. Today, the Seychelles archipelago is an important centre of endemism for many plants and animals, including amphibians. The four known Sooglossid species have only been recorded from the two highest (Mahé and Silhouette) of the 115 islands in the archipelago, where they live in the mountain mist forests. They are Sooglossus gardineri found on Mahé and Silhouette; Sooglossus pipilodryas found on Silhouette only; Sooglossus sechellensis found on Mahé and Silhouette; and Nesomantis thomasseti found on Mahé and Silhouette.

Smallest frogs in the world

The sooglossidae are tiny frogs: the smallest species Sooglossus gardeneri, believed to be the tiniest frog in the world, measures just about 9-12 mm long. Their newly emerged juveniles measure only 1.6 mm long, and are literally almost too small to see.  The Sooglossus sechellensis is about 15 to 18 mm long and the Nesomantis thomasseti is slightly bigger, about 35 to 45 mm long.

What do they eat

The diet of Sooglossus gardineri consists mostly of mites, sciarid fly larvae, ants and amphipods, while Sooglossus sechellensis is known to consume termites.  Nothing is known about the feeding ecology of Nesomantis although it probably eats correspondingly larger prey than the other species.

Conservation Status

Because of their extremely limited global distributions (less than 100km2 of montane forest) three of the species are listed on the IUCN Red List of threatened species: Sooglossus gardineri –Vulnerable, Sooglossus sechellensis –Vulnerable, and Nesomantis thomasseti –Endangered. Sooglossus sechellensis actually appears to be the rarest species, rather than Nesomantis thomasseti, which is still fairly common.  Sooglossus gardineri is very abundant and widespread.  The fourth Sooglossus pipilodryas was discovered too recently to be listed, although it too no doubt will be in due course.

Silhouette, with an area of 20 km2 and a population of less than 150 people, faces few immediate threats.  This island currently appears to support healthy populations of the three species of Seychelles frog listed above, plus the recently discovered (2002) palm frog, Sooglossus pipilodryas. However, new hotel and infrastructure development might be a potential threat to these species.

In contrast, Mahé has a population of over 70,000 people and, although it is a much larger island at 148 km2, faces steadily growing development pressures.  With space at a premium on the island, these pressures increasingly include the residential development of montane forest.  While important areas of Seychelles frog habitat are now protected within the 30.5 km2 Morne Seychellois National Park in north Mahé, the current status of the three species known to occur here is unclear.  Moreover, significant tracts of potentially suitable habitat in Mahé’s central and southern mountains lack any protection against encroaching development, and the distribution and status of Seychelles frogs in these areas is completely unknown.

What we have done

Very little monitoring work has been carried out on the main island of Mahe and consequently little was known about their status. Concern about the dramatic global declines of many amphibian populations prompted Nature Seychelles to initiate a project to investigate the status of these unique frogs on Mahe. With support from the Royal Society for Protection of Birds (RSPB) and the Herpetological Conservation Trust in the United Kingdom, a scoping study of the sooglossids on Mahe was undertaken.

What we are doing

Our scoping study trailed methods and recommended the most practical method for determining distribution and numbers in the field, outlined a long-term monitoring programme for regular assessment of the frogs status and abundance and identified priority research needs. With this information Nature Seychelles is implementing a programme to look at the long-term status of these frogs.