Family Brevicipitidae

Breviceps sylvestris FitzSimons, 1930

Northern Forest Rain Frog, Transvaal Forest Rain Frog, Forest Rain Frog, Senana (P), Transvaal Woudblaasoppadda (A)

By L.R. Minter

Currently accepted name: Breviceps sylvestris FitzSimons, 1930
Red listing status: Near Threatened (IUCN ver 3.1, 2016)

Photo by Diedericks G., 2010. URL: FrogMAP: 45

RED LIST SPECIES

Status: Vulnerable (VU) Criteria: B1ab(ii,iii,iv,v) + 2ab(ii,iii,iv,v)

Identification

B. sylvestris occurs in parapatry with B. adspersus throughout its range. The subspecies B. s. sylvestris occurs in sympatry with B. mossambicus, which occupies montane grassland adjacent to forest patches along the escarpment. There is also a possibility that B. s. sylvestris occurs in sympatry with B. verrucosus between Legalameetse and Mariepskop.

The granular texture and mottled markings of the skin of the abdomen, and the presence of a pair of longitudinal glandular ridges on the dorsum, distinguish both B. sylvestris and B. verrucosus from B. adspersus and B. mossambicus, which have a smooth, immaculate abdomen and lack dorsal skin ridges. The advertisement calls of B. sylvestris and B. verrucosus consist of a series of long, evenly spaced, pulsed whistles, averaging 0.36 and 0.61 s in duration respectively, while those of B. adspersus and B. mossambicus are much shorter (0.08 and 0.2 s in duration, respectively) and are often emitted in groups of two, three or more calls within a bout of calling (Minter 1998).

In B. sylvestris, the tympanum is indistinct and, in most cases, cannot be distinguished from the surrounding granular skin, while in B. verrucosus it is usually smooth and fairly obvious. B. sylvestris is further characterized by a broad, light margin to its down-turned mouth, giving its face a clown-like appearance. The advertisement calls of B. sylvestris and B. verrucosus are very similar, differing only in duration (see above) and call rate: 69 and 22 calls per minute, respectively (Minter 1998).

Distribution

B. sylvestris is endemic to Limpopo Province, where it occurs on the slopes and crests of the Blouberg, Soutpansberg, Wolkberg and Drakensberg ranges. It is locally abundant but its distribution is restricted to isolated fragments of its natural habitat that have not yet been subjected to afforestation or other forms of agriculture. The subspecies B. s. sylvestris is recorded from Haenertsburg (2329DD), eastward to Tzaneen (2330CC) and southward along the eastern escarpment as far as Legalameetse Nature Reserve (2430AB), while B. s. taeniatus occurs in the Soutpansberg Mountains from Blouberg (2328BB) eastward to Thoyandou (2230CD). The two subspecies are geographically isolated by about 80 km of unsuitable habitat.

Legalameetse, with the southernmost recorded population of B. sylvestris, is separated by a distance of about 70 km from the northernmost recorded population of B. verrucosus, at Mariepskop (2430DB). The area separating these species is rugged and rather inaccessible and was not sampled during the atlas project. However, it contains suitable breeding habitat and should be surveyed to determine whether the two species occur in sympatry.

The existing atlas data are reliable, as B. sylvestris is easily identified by its appearance and its call. However, further sampling is required in areas of suitable habitat within the limits of its known range.

Habitat

The breeding and non-breeding habitat is Afromontane Forest and adjacent North-eastern Mountain Grassland. In the breeding season, males call from closed-canopy forest, the forest fringe and adjacent open grassland in mountainous terrain. Calling males have also been encountered in disturbed habitats such as wooded parks and gardens, and in pine plantations on the fringe of indigenous forest. In winter, specimens have been found under rocks and logs in indigenous forest (Minter 1998).

Life history

B. sylvestris constructs an extensive network of shallow, horizontal tunnels and chambers below the soil surface and under rocks and logs (pers. obs.). The dry winter months are spent underground, but rain at this time of year may result in surface activity and some calling. Aestivation, involving the production of a cocoon, has not been observed.

Most breeding takes place after rain in early spring, that is, September–October, but continues into early December (Minter 1998). In wet, misty weather, large choruses develop and continue, unchecked, for several consecutive days and nights.

At night, during rain or heavy mist, males call while moving about on the surface, sometimes climbing to an elevated position on a grass tuft or herbaceous plant. During the day, in wet weather, they call from well-concealed, shallow depressions beneath leaf litter (Minter 1998). Amplexus is adhesive and nests are constructed below the surface, at the base of a rock, log, or amongst tree roots. Thompson (in Wager 1965) recorded a mass of 56 eggs covered by a layer of infertile eggs; the female remained in a tunnel adjoining the egg chamber until the young were fully developed, and removed soil that fell onto the egg-mass. Jacobsen (1989) found a female with an egg-mass in November.

Prey items have not been documented but probably include various invertebrates characteristic of the forest floor.

Conservation

Status

B. sylvestris was not listed in earlier South African Red Data books (McLachlan 1978; Branch 1988) but was listed as Near Threatened by Harrison et al. (2001). Reassessment for this publication has placed it in the Vulnerable category based on the species’ severely fragmented and restricted distribution (area of occupancy: 501–2000 km), rate of habitat loss (>20% in the last 50 years) and predicted population decline (>20% in the next 30 years).

B. sylvestris occurs in the following provincial nature reserves: Blouberg, Blouberg-Maleboch, Happy Rest, Thabina, Lekgalameetse; state forests: Entabeni, Hanglip, Woodbush, and Black Forest; and the Wolkberg Wilderness Area. It is protected by the Limpopo Province Department of Environmental Affairs and Tourism Conservation Ordinance 12 of 1973, and the National Forests Act 19408 of 1998, Section 7. Outside of the relevant areas it is unprotected except for collecting and export control.

Threats

The major threats to B. sylvestris are habitat loss and fragmentation due to afforestation and other agricultural practices. These activities also impact negatively on the quality of the remaining habitat by reducing the quantity of surface and soil water and altering natural fire regimes in adjacent areas. Water and fire are key limiting factors that influence the distribution and extent of Afromontane Forest patches (Low and Rebelo 1996). The networks of roads developed to sustain these agricultural activities also fragment previously continuous areas of suitable habitat, while road kills during the breeding season are believed to contribute significantly to population declines.

Recommended conservation actions

A detailed survey should be carried out to identify the location and size of all the remaining populations of this endemic, restricted-range species. A study of the extent to which the two subspecies of B. sylvestris have diverged genetically, and a similar comparison between B. sylvestris and B. verrucosus, would further clarify the conservation status of this species.

Management recommendations include habitat and limiting factor management and the establishment of a monitoring programme, both inside and outside reserves. In view of the restricted distribution of B. sylvestris, priority should be given to the conservation and management of the remaining indigenous forests and grasslands, the breeding habitats of this, the only frog species endemic to Limpopo Province.

Current distribution map

Undated records;  pre-1996;  1996 to 2002;  2003 to present