Family Pyxicephalidae

Pyxicephalus edulis Peters, 1854

Edible Bullfrog, Lesser Bullfrog, African Bullfrog, Kleinbrulpadda (A)

By C.L. Cook and L.R. Minter

Currently accepted name: Pyxicephalus edulis
Red listing status: Least Concern

Photo by Hankey Andrew, 2008. URL: FrogMAP: 121

Distribution

Formerly synonymized with P. adspersus (Poynton 1964) and later treated as a subspecies of P. adspersus (Parry 1982; Poynton and Broadley 1985b; Lambiris 1989a), this taxon was again recognised as a full species by Channing et al. (1994a) on the basis of clear differences in advertisement call and breeding behaviour. At present there appear to be no reliable, diagnostic, morphological characters that allow one to distinguish P. edulis from small individuals of P. adspersus (Channing et al. 1994a). For this reason, museum specimens and literature records, unless accompanied by call or other relevant behavioural data, have to be treated with circumspection.

Outside of the atlas region, P. edulis occurs in Mozambique (Channing et al. 1994a) and extends into Kenya (Channing 2001). The species is probably widespread in Central and East Africa: in Malawi, for example, males do not exceed 120 mm in snout–vent length (Stewart 1967) and may, therefore, belong to P. edulis. Its presence along the northeastern border of South Africa indicates that P. edulis is also likely to occur in Botswana and Zimbabwe.

In the atlas region, records based on calls were collected in the northeastern parts of North West Province, Limpopo Province, eastern Mpumalanga Province, northern and eastern Swaziland and northeastern KwaZulu-Natal as far south as Empangeni (2831DD).

Fieldwork involving the collection of advertisement calls and knowledge of intra- and inter-specific variation in the morphology of adults, juveniles and tadpoles, is required before the distribution of this species can be accurately mapped (Channing et al. 1994a; Channing 2001).

The atlas data are reasonably reliable given the problems outlined above, but are not comprehensive.

Habitat

In the atlas region, this species inhabits several bushveld vegetation types in the northeastern parts of the Savanna Biome, from sea level to an altitude of about 1500 m (Jacobsen 1989).

Flat, low-lying areas in open, grassy woodland, that become flooded after heavy rain or contain shallow, seasonal pans, constitute prime breeding habitat and support large breeding populations (e.g., in Kruger National Park, Naboomspruit, Vivo, Soekmekaar and Giyani districts). Smaller breeding aggregations form in artificial impoundments such as roadside furrows, borrow pits, waterholes, ponds and dams (Jacobsen 1989; L.R.M. pers. obs). Channing et al. (1994a) found this species breeding in rice paddies in Mozambique.

Life history

P. edulis spends up to 10 months of the year in a dormant state beneath the soil surface (Mitchell 1946). The production of a cocoon to prevent desiccation has not been observed, but Stewart (1967) noted that “when hibernating during the dry season, eyes are closed and depressed to the level of the head”.

Breeding takes place at night (cf. P. adspersus) after heavy rain. No aggressive behaviour was observed in a breeding population near Beira (Channing et al. 1994a), but in Kruger National Park, males calling at distances of 0.5–1.5 m from each other in shallow, flooded grassland were seen charging one another (L.R.M. pers. obs.). However, this species does not appear to display the same level of aggressive behaviour as P. adspersus. Males call from the water, with only the head and vocal sac projecting above the surface. Guarding of tadpole swarms and channel construction by males were observed in a breeding population of P. edulis near Jock of the Bushveld Rest Camp in the Kruger National Park (H. Braack pers. comm.).

Food items include a variety of invertebrates and small vertebrates, including frogs. Several bird species, Nile Monitors Varanus niloticus and humans are known to prey on this species (Peters 1882; Stewart 1967; Channing 2001).

Conservation

The occurrence of this species in the atlas region is marginal in terms of its global distribution. Within this area it is relatively common and does not appear to be at risk. Large populations are known to occur in private and provincial nature reserves and national parks, such as Kruger National Park. The effect of human predation outside protected areas should be evaluated. More detailed studies of habitat requirements, breeding biology, duration of the larval stage and development are recommended for this species.

Current distribution map

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