Family Pyxicephalidae

Natalobatrachus bonebergi Hewitt and Methuen, 1913

Kloof Frog, Boneberg’s Frog, Kloofpadda (A)

By L.H. du Preez

Currently accepted name: Natalobatrachus bonebergi
Red listing status: Endangered

Photo by Evans Nick, 2013. URL: FrogMAP: 1074

RED LIST SPECIES

Status: Endangered (EN) Criteria: B2ab(ii,iii,iv)

Identification

N. bonebergi is a small- to medium-sized frog, females reaching 37 mm and males 25 mm in length. They are usually brown, but may be light to greenish brown. The snout is pointed, projecting markedly over the lower jaw. The fingers and toes are long with large, truncated, terminal discs, and the toes are slightly webbed. The back has elongated skin ridges, and a light vertebral stripe is often present. A distinct black stripe runs from the tip of the snout, through the lower part of the eye to the arm.

Distribution

N. bonebergi is endemic to the atlas region and restricted to the coastal forests of southern KwaZulu-Natal and northern Eastern Cape provinces, at altitudes below 900 m. The species is known from 18 quarter-degree grid cells, but was found in only five during the atlas period. The southernmost records are from Dwesa Nature Reserve (3228BB).

The atlas data are reliable but incomplete, especially with regard to recent records from the northern parts of the species’ range.

Habitat

N. bonebergi is always associated with forest streams and pools with rocky beds especially, but not exclusively, in ravines (Harrison et al. 2001). Typically, the frogs inhabit streams with short, fast-flowing sections alternating with longer sections of slow-flowing water and pools of varying size and depth. Eggs are deposited on vegetation or rock surfaces overhanging water.

Life history

These frogs are strong jumpers and can be difficult to catch. They take readily to water, swim well, and usually dive to the bottom where they hide in rotting plant material.

Breeding takes place October–May, along shallow streams with overhanging vegetation. Males select perches c.1–2 m above the water, from which they utter their faint advertisement calls. Amplexus is axillary with the fingers of the male placed below or sometimes above the base of the female’s arms. Transparent masses of 75–95 eggs are attached to leaves, twigs, tree trunks, or rock surfaces overhanging pools. The diameter of the egg mass is 75–108 mm, and the diameter of eggs is 1.5–2 mm, in 4-mm jelly capsules. Clutches may be placed in positions from just above water level to >2 m above the water, with a reported mean of 580 mm (Kok and Seaman 1989). Egg clutches are vulnerable to desiccation; in dry conditions the female moistens the clutch with liquid from her cloaca (pers. obs.).

After six days, the tadpoles are ready to wriggle out of the egg mass that becomes more liquid and sags downward. On hatching, tadpoles drop into the water to complete their development. Tadpoles are benthic and can complete metamorphosis in 60 days.

Conservation

Status

N. bonebergi was not listed in previous Red Data books. In view of its restricted distribution (area of occupancy = 11–500 km²) and rate of habitat loss (>50% in the past 100 years), it has been accorded Endangered status (Harrison et al. 2001; this publication).

N. bonebergi occurs in Vernon Crookes, Oribi Gorge, Krantzkloof, Umtamvuna, Dwesa and Cwebe nature reserves.

Threats

Threats include the loss of habitat resulting from urbanization along the south coast of KwaZulu-Natal, wood-cutting in gallery forests, and crop agriculture in the form of sugar cane and tree plantations. Cooper (1988) estimated that 90% of the Coastal Forest of KwaZulu-Natal had been destroyed for the cultivation of sugar cane. Pollution and siltation of streams are factors that degrade habitat. Kok and Seaman (1989) identified three major threats to this species: the destruction of water courses and wetlands in unprotected areas, forest denudation by firewood collectors, and pollution.

Recommended conservation actions

Surveys are required to identify new populations, and known populations should be monitored: anyone walking through indigenous forest in the rainy season should be on the lookout for this interesting frog and its egg masses.

There is an urgent need to protect and manage the remaining habitat of this unique endemic species. Research into limiting factors is needed. Where remnants of gallery forest exist on private land, landowners should be informed about this species and its habitat requirements.

Current distribution map

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