Family Bufonidae

Bufo pantherinus A. Smith, 1828

Western Leopard Toad, August Frog, Leopard Toad, Westelike Luiperdskurwepadda (A)

By A.L. de Villiers

Currently accepted name: Sclerophrys pantherina (Smith, 1828)
Red listing status: Endangered

Photo by Hodgson Andrew & Heather, 2010. URL: FrogMAP: 25

RED LIST SPECIES

Status: Endangered (EN) Criteria: B1ab(ii,iii,iv,v)+2ab(ii,iii,iv,v)

Identification

B. pantherinus was formerly regarded as an allopatric population of B. pardalis, separated from the latter by a distance of more than 300 km. Poynton and Lambiris (1998) raised B. pantherinus to the status of a full species on the basis of colouration, markings and morphological differences between the two populations. Furthermore, Eick et al. (2001) found greater genetic divergence between B. pantherinus from the Western Cape and B. pardalis from the Eastern Cape than within either area, and agreed that B. pantherinus is specifically distinct from B. pardalis. However, Cunningham and Cherry (2000) found only 0.5% divergence between the populations and felt that this was insufficient to warrant full species status for the Western Cape population.

While the advertisement call of B. pardalis (in the Eastern Cape) has been described (Passmore 1977b), an adequate comparison of the calls of B. pardalis and B. pantherinus has not been published (Poynton and Lambiris 1998). Thus the taxonomic status of the two populations has not been fully resolved.

B. pantherinus attains a length of about 140 mm. The beautiful dorsal pattern of chocolate-brown patches on a bright yellow background, with a yellow vertebral stripe, distinguishes this species from the partially sympatric B. rangeri that has generally dull brown dorsal markings, and B. angusticeps that, in this area, has a greyish dorsal surface covered in dark brown blotches, and yellow colouring on the upper surfaces of its feet. The ventrum of B. pantherinus is granular and cream-coloured, with a darkish throat in males.

The advertisement call, a deep, pulsed snore that continues for about a second and is repeated every three to four seconds, easily distinguishes B. pantherinus from all other sympatric toad species.

Distribution

B. pantherinus is endemic to the winter-rainfall region of the Western Cape. It has a restricted distribution range that spans a distance of about 140 km, from the Cape Peninsula (3318CD, 3418AB) in the west, eastward to beyond Gansbaai in the Pearly Beach area (3419DA). The species has a distinctly coastal distribution and is generally associated with low-lying areas within about 10 km of the sea. Its distribution correlates with large wetland areas, including rivers, and an annual rainfall of ≥600 mm.

The earliest distribution records of B. pantherinus were obtained from the Cape Peninsula and adjoining southwestern part of the Cape Flats (3318CD, 3418AB, BA). This area has also produced the most distribution records, including the following localities: Observatory, Valkenberg, Hout Bay, Noordhoek, Sun Valley, Fish Hoek, Clovelly, Kalk Bay, Kommetjie, Glencairn, the Cape of Good Hope Nature Reserve (northern limits), Scarborough, Constantia, Bergvliet, Tokai, Diep River, Kirstenhof, Lakeside, Rondevlei, Zeekoevlei, Southfield, Ottery, Philippi, Strandfontein and some neighbouring areas. Although Poynton (1964) recorded B. pantherinus occurring on the Cape Flats in grid cell 3318DC, no further records are known from this area. The mapping of this grid cell represents Poynton’s interpretation of South African Museum specimens from the “Cape Flats”. The species is more likely to have been recorded from the Cape Flats area immediately to the south, situated in grid cell 3418BA where there are known former and current localities.

In the coastal region to the southeast, B. pantherinus has been recorded from Pringle Bay and Betty’s Bay (3418BD), Kleinmond (3419AC), Hermanus and Stanford (3419AD), Gansbaai and Uilenkraalsmond (3419CB), and the Pearly Beach area (3419DA).

In summary, B. pantherinus has been recorded from eight quarter-degree grid cells. Since 1995, it has been found in six of these cells of which 3419CB represents a new record. There are no recent records for cells 3318CD and 3419AC.

Habitat

B. pantherinus is mainly associated with sandy coastal lowlands but, in places, can also be found in valleys and on the lower mountain slopes and hills near the coast. It is a wide-ranging species and, although it seems to spend most of its time away from water, this toad is always found in the general vicinity of wetland habitats such as rivers, coastal lakes, vleis and pans.

It inhabits the Fynbos and Thicket biomes where it is found in the following vegetation types: Mountain Fynbos, Laterite Fynbos, Limestone Fynbos, Sand Plain Fynbos and Dune Thicket. However, the species is not restricted to pristine natural habitats and is often found in modified habitats such as farmlands, urban open spaces and suburban gardens. Breeding has also been recorded in wetlands where some degree of pollution and eutrophication is evident.

This species generally breeds in permanent water bodies but also in seasonal wetlands that retain their water well into the summer months. Breeding habitat includes coastal lakes, vleis, pans, dams, ponds and sluggish, meandering rivers that have stretches of relatively deep, still water. Typical breeding sites have standing open water >50 cm deep, with scattered patches of aquatic plants and beds of emergent vegetation such as bulrushes Typha capensis.

Life history

B. pantherinus is an explosive breeder with a short, defined breeding season (Cherry 1992). Breeding usually takes place during August but has also been recorded at the end of July and in September. At the commencement of the breeding season, large numbers of adults appear and converge on selected breeding sites, hence the old popular name, “August frog”. For example, after dark on 23 July 1978, 66 adults were counted within c.20 min on a 3-km stretch of road near Noordhoek on the Cape Peninsula.

At prime breeding sites, advertisement calls of males can be heard in choruses of up to c.30 individuals, but in urban environments far fewer individuals are usually heard. Calling is most intense at night but is sometimes heard during the day. Males call from stands of emergent vegetation (e.g. bulrushes), but at night, areas of open water are also utilized. The males have a habit of calling from a floating position with limbs outstretched. Amplexing pairs tend to utilize areas of open water for spawning (Cherry 1992).

The females deposit thousands of eggs in gelatinous strings. On one occasion a pair was reported to have produced 24 476 eggs (Rose 1929). Metamorphosis is fairly slow, taking >10 weeks. The relatively small, dark, benthic tadpoles develop into tiny 11-mm long toadlets that leave the water in October–December in their thousands. Relatively few of the offspring develop into adults: most fall victim to a variety of predators (including their own kind) and other hazards.

Conservation

Status

There appears to be no obvious decline in the extent of occurrence of B. pantherinus. However, urban development has resulted in permanent loss of habitat and the fragmentation of populations, especially on the Cape Peninsula and Cape Flats. In other areas, habitat degradation has affected habitat quality and led to a decline in population numbers.

Although this toad occurs in some of the protected nature areas within its range, these generally lack suitable breeding habitat. In fact, most of the protected areas in the southwestern Western Cape Province are located in montane areas, while probably >80% of B. pantherinus breeding habitat is situated lower down in unprotected areas. Zandvlei Nature Reserve (including the adjoining Westlake Wetland Conservation Area) is one protected area with good breeding habitat. Other statutory conservation areas that provide breeding habitat include Rondevlei and Zeekoevlei nature reserves and Cape of Good Hope Nature Reserve (northern limits), but the quality of this habitat is unknown.

In the municipal areas of the Cape Peninsula and Cape Flats, B. pantherinus is known to breed in certain public open space and green-belt areas and is often encountered in surrounding gardens. These are important sanctuaries, but with increasing development, road traffic and associated threats, the survival of local populations could be threatened.

The recognition of the species status of B. pantherinus has resulted in its being classified Endangered (Harrison et al. 2001; this publication). This is based on an extent of occurrence <5000 km², an area of occupancy <500 km², a severely fragmented habitat, continuing decline in the extent of occurrence, area of occupancy, extent and quality of habitat and the number of locations/subpopulations and mature individuals. The species is legally protected by the Nature Conservation Ordinance 19 of 1974, but is not listed by CITES.

Threats

B. pantherinus is threatened throughout most of its range by general development and habitat degradation. While breeding generally takes place in larger, more secure wetlands, urban development poses an obvious threat around these wetlands by causing habitat fragmentation and restricting the foraging area and movement of toads. This results in reduced population size and restricted or completely interrupted gene flow between populations.

In the urban environment, toads are forced to negotiate roads and barriers (e.g., walls, embankments, canals) while foraging and migrating to and from breeding sites. Expanding urban development and increased road traffic results in the death of hundreds of toads each year, especially during the breeding season. Artificial water bodies with steep vertical sides, such as canalized rivers and swimming pools, represent additional deathtraps that pose a threat to local populations. For example, >3000 newly metamorphosed toadlets were rescued from a Bergvliet domestic swimming pool over a 10-day period, and many more died in the same pool (J.A. Harrison and C.D. Gray pers. comm.).

At certain breeding sites on the Cape Peninsula and the Cape Flats, specific threats include pollutants, introduced predatory fish (e.g. barbel), and invasive floating plants (e.g. water hyacinth).

In 1999, a well-meaning member of the public “rescued” several specimens of B. pardalis and B. rangeri from roads near Grahamstown in the Eastern Cape, and released them in Constantia, Cape Peninsula (M. Burger pers. comm.). This misguided act may have brought about hybridization between B. pardalis and B. pantherinus, thereby undermining genetic differences between the two taxa. Such translocations may be common occurrences and pose a real threat to the conservation of genetic diversity.

Recommended conservation actions

The distribution and conservation status of B. pantherinus is monitored by the Western Cape Nature Conservation Board (De Villiers 1997a). A priority of this body is to identify and improve the conservation status of breeding sites and surrounding foraging areas. The effect of pollutants and introduced predatory fish on the development of eggs and tadpoles requires further investigation. Further publicity should be given to the plight of this toad to encourage public support for the conservation of the species.

In recent years, B. pantherinus has featured in various environmental scoping and impact assessment reports for areas within the Cape Metropolitan Area. With the increasing development of this area, it is important that unprotected key breeding sites and, where possible, adjacent foraging areas, be protected, managed and monitored. Furthermore, public open spaces supporting important breeding sites should be linked, where possible, by appropriate road reserves and green-belt corridors. This would facilitate the movement of toads among breeding sites, maintain gene flow, and prevent the isolation of breeding populations. The establishment of suburban conservancies could help to maintain secure populations in built-up areas.

The attractiveness of B. pantherinus and its threatened status may necessitate inclusion on the CITES list to protect the species against possible illicit trade.

Current distribution map

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