Family Bufonidae

Bufo gariepensis A. Smith, 1848

Karoo Toad, Karoo Skurwepadda (A)

By M.F. Bates

Currently accepted name: Vandijkophrynus gariepensis gariepensis
Red listing status:

Photo by Loftie-Eaton M; V. Jessnitz, R. Jessnitz, 2013. URL: FrogMAP: 1303

Distribution

B. gariepensis is distributed mainly south of 28°S and west of 30°E, but its range extends northward along the Transvaal Drakensberg range, through Mbabane in northwestern Swaziland, to the Lydenburg-Sabie area of Mpumalanga Province (2530BA). Atlas records indicate that the species has a much larger range in the Northern Cape Province than is shown on Poynton’s (1964) map.

Outside of the atlas region, the species crosses the Gariep (Orange) River (often reduced to a trickle in the dry season) into southern Namibia, while an isolated population is present on the Nyanga Mountains in eastern Zimbabwe. The advertisement call of the latter, B. gariepensis inyangae, is unknown, but based on mitochondrial-DNA sequences, Cunningham and Cherry (2000) considered it to be a distinct species.

The subspecies B. gariepensis nubicolus occurs along the summit of the KwaZulu-Natal Drakensberg from Mont-aux-Sources (2828DD) southward to Sani Pass (2929CA) and to Naude’s Nek (3028CA) in the southwest. It occurs at altitudes up to c.3400 m. Although specimens from this area differ consistently from typical B. g. gariepensis in certain ways, most notably in colour pattern (see Passmore and Carruthers 1995), the same characters are of less diagnostic value in populations from the eastern Free State (Bates 1995) and Lesotho (Bates and Haacke 2003).

While populations from Mpumalanga and Swaziland were treated as B. gariepensis gariepensis by Poynton (1964) and Boycott (1992), Jacobsen (1989) referred populations in Mpumalanga to B. g. nubicolus. Branch and Braack (1989) referred to two ecomorphs occurring in Karoo National Park, namely a “brightly-patterned nubicola form from the upper plateau” and “more typical gariepensis that is larger and duller in colour, from the lower plains”. Branch and Braack (1995) suggested that B. g. nubicolus be raised to species status and that certain isolated montane populations, currently referred to B. g. nubicolus (e.g., Bamboesberg Mountains 3126CA; Nuweveldberg Mountains, Karoo National Park 3222BC), may prove to be separate species. Further investigation is needed to clarify these issues.

In the Richtersveld, B. gariepensis occurs along the banks of the Gariep River, while a similar species, B. robinsoni, inhabits springs and temporary water sources. However, the latter has a substantially different advertisement call and, in this area, can also be distinguished from B. gariepensis by its orange back with green spots, poorly developed parotoid glands, weakly developed tarsal fold, small tympanum, relatively smooth skin, and relatively large eye (Branch and Braack 1995).

In Namaqualand, B. robinsoni loses the bright colouration that is typical of the species in the rocky Richtersveld and Ghaamsberg areas, and approaches the drab colour and pattern generally attributed to B. gariepensis. Conversely, juvenile B. gariepensis in rocky habitats frequently show the bright colour patterns attributed to B. robinsoni (H. Braack pers. comm.). In this area the two species may be positively identified by their advertisement calls. At Nieuwoudtville (3119AC), B. gariepensis and B. angusticeps have been found breeding in the same pools, and are extremely difficult to separate except by call (H. Braack pers. obs.).

The atlas data for B. gariepensis is reliable, except in areas of sympatry with B. robinsoni and B. angusticeps where records based on identification using morphology alone should be viewed with circumspection.

Habitat

B. gariepensis has been recorded from the Nama Karoo, Succulent Karoo, Fynbos, Thicket and Grassland biomes and occurs in both summer- and winter-rainfall regions. It is adapted to survive in extremely arid areas and, in at least parts of its range, it can tolerate very low temperatures. On the Nuweveldberg Mountains in Karoo National Park, specimens were observed moving about in the snow; these frogs may have been disturbed and forced to seek shelter in new refuges (H. Braack pers obs.).

The species is found in a variety of habitats, including open, sandy areas in the semi-arid Karoo, and grassland in the eastern parts of its range. In the Free State and most of Lesotho, it occurs in mountainous and rocky areas where it may be found under rocks, in burrows under rocks, and occasionally in abandoned termitaria(Trinervitermes sp.). At high elevations in the KwaZulu-Natal Drakensberg, B. g. nubicolus occurs in short, sparse, open grassland where specimens have been found under vegetation or stones, in swampy areas, and in temporary pools.

Breeding habitats include a variety of water bodies, both permanent and temporary, such as streams, dams, roadside rain pools, quarries, pans, seepages and spongy bogs. The species has even been found breeding in water-filled hoof prints of cattle in the Drakensberg, and in a small pool under a leaking tap at Sendelingsdrift in the Richtersveld!

Life history

In Namaqualand, B. gariepensis is an opportunistic breeder. Most breeding takes place during the winter rains, but also during summer if sufficient water is available (Channing 1988). It has been recorded spawning in September and February in the Western Cape (Visser 1979a), and breeds in late summer and autumn in the summer-rainfall Karoo and Bushmanland (H. Braack pers. obs.). Tadpoles were collected during September in both Worcester (Western Cape) and near Harrismith (Free State), while in the Richtersveld, calling was heard September–March (H. Braack pers. obs.). In Lesotho, B. g. gariepensis tadpoles were collected in early October and in November and December in pools and at the sides of streams (new atlas data). Males may call during daylight hours in overcast or rainy weather, as well as at night.

Wager (1965) recorded the following breeding details for B. g. nubicolus. Strands of 100 or more eggs are laid in small shallow depressions in sponge-like bogs fed by springs on the summit of the Drakensberg. The tadpoles form a squirming mass and grow to a maximum length of 24 mm after only a few days. According to Lambiris (1988e), metamorphosis is usually completed after c.20 days.

In the Drakensberg Mountains, prey consists of small arthropods (Lambiris 1988e). Two specimens of B. gariepensis that were offered to a captive Water Mongoose Atilax paludinosus, were flipped over onto their backs and eaten from the belly, presumably to avoid toxins in the dorsal glands: one specimen was partly eaten while the second was entirely consumed (Stuart 1981).

Conservation

B. gariepensis is recorded from Mountain Zebra National Park in the Eastern Cape, Gamka Nature Reserve in Western Cape Province (Branch 1990) and Richtersveld National Park in Northern Cape Province (Branch and Braack 1995). It also occurs in Karoo National Park at Beaufort West and in Karoo Nature Reserve at Graaff Reinet. In the Free State it has been recorded from Golden Gate Highlands and Qwa-Qwa national parks and Tussen-die-Riviere Game Farm (Bates 1997). Although it has not been found in Blyde River Canyon Nature Reserve in Mpumalanga, it occurs nearby in Long Tom Pass.

B. gariepensis has an extensive distribution range and is abundant, but some isolated populations may be speciating. Branch and Braack (1995) noted that “a detailed study of vocalization, supplemented with biochemical analysis, of montane isolates of B. g. nubicolus and B. g. inyangae may demonstrate a suite of cryptic species”. These isolated populations should be considered evolutionarily significant units, warranting protection and regular monitoring.

Current distribution map

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