Family Pyxicephalidae

Anhydrophryne rattrayi Hewitt, 1919

Hogsback Frog, Rattray’s Frog, Rattray’s Forest Frog, Hogsback Padda (A)

By M. Burger

Currently accepted name: Anhydrophryne rattrayi Hewitt, 1919
Red listing status: Vulnerable B1ab(iii) (2016)

Photo by Grundlingh Felicity, 2012. URL: FrogMAP: 632

RED LIST SPECIES

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

Identification

This is one of southern Africa’s smallest frog species with females attaining a body length of 22 mm. The snouts of males are calloused, slightly flattened, usually whitish and presumed to be adapted for excavating nests. Body colour and pattern are variable: the dorsum varies from light grey to dark brown or copper-coloured. Irregular dark mottling and a thin, light vertebral line are sometimes present. A dark mask extends across the eyes from nostrils to armpits. The white ventrum is marbled with dark blotches that do not extend onto the throat (Wager 1963, 1986; Passmore and Carruthers 1995; Channing 2001). (See genus account for further distinguishing characters.)

The advertisement call has been described as a melodious “ping, ping, ping”, repeated rapidly or slowly in bouts of 7–15 notes, or sometimes emitted as single notes (Wager 1986). The notes are 0.05 s in duration with an emphasized frequency of 3500 Hz (Channing 2001). Passmore and Carruthers (1995) recorded a call rate of 4 notes/s, emitted at an emphasized frequency of 3000 Hz.

Distribution

A. rattrayi is endemic to the Eastern Cape Province where it has a restricted distribution centred in the Amatola Mountains. The species was originally discovered at Hogsback Mountain and was subsequently recorded from forests at Katberg, Stutterheim, Keiskammahoek and Peddie mountains (Wager 1963, 1986; Lambiris 1988a; Castley 1997), although the last-mentioned locality may be incorrect. No new locality records were obtained during the atlas project, and only two of five quarter-degree grid cells, in which the species has been recorded, were confirmed during the atlas period. The species was recorded near Patensie (3324DB) by Visser (1979d), based on a specimen he collected in 1961. This record represents a considerable range extension to the southwest, but could not be confirmed during the atlas period or at any time since the initial observation. Nevertheless, the record is believed to be valid (J.D. Visser pers. comm.). The record at 3327AA (Lambiris 1988a) is apparently an error.

The atlas data give a fairly comprehensive representation of the species’ distribution, but there are few recent (post-1996) records.

Habitat

The species inhabits Afromontane Forest at altitudes generally >1100 m. It breeds in moist leaf litter on the forest floor, often near streams and waterfalls. It appears to flourish in the grassland/forest ecotone and also occurs in short grass in small open patches of wetland within forests. Adults are found in wet situations (e.g. near waterfalls), but the eggs are laid in areas where waterlogging is unlikely to occur (Wager 1986; Lambiris 1988a; Passmore and Carruthers 1995; Channing 2001).

Life history

Although it has a restricted distribution, A. rattrayi occurs in large numbers at some localities. For example, Lambiris (1988a) counted >70 individuals within c.25 m² in a grassland/forest ecotone. Under favourable conditions, that is, mist or rainy weather, hundreds of males may be heard calling throughout the night and sometimes during the day. Calling has been recorded in summer, October–February (Wager 1986; Channing 2001).

The species reproduces by direct development. Eggs are laid in small holes excavated in the clay soil beneath leaf litter on the forest floor. Wager (1986) recorded a spherical egg chamber, 21 mm in diameter, with a smooth shiny wall and a 9-mm entrance hole in the 3-mm thick roof. The chamber is, apparently, excavated by males. Additional information on nest building and other aspects of reproductive biology is needed.

The pearly white eggs are large, nearly 2.6 mm in diameter, and encased in a 6-mm gelatine capsule. Clutches of 11–20 eggs are laid in a single layer on the floor of the nest and adhere to each other. Larval development and metamorphosis are completed in about four weeks. The newly metamorphosed froglets measure only 4 mm from snout to vent (Wager 1986).

The diet of A. rattrayi includes small leaf-litter crustaceans such as amphipods and isopods (Wager 1986). Collembola appear to form a large proportion of the diet (Lambiris 1988a).

Conservation

Status

A. rattrayi is here classified as Endangered owing to its limited and severely fragmented distribution. It was previously listed as Restricted (Lambiris 1988a) and Near Threatened (Harrison et al. 2001; IUCN 2000).

A. rattrayi is known from Stutterheim Nature Reserve and state forests between Keiskammahoek and Hogsback, including Hogsback Indigenous Forest and Katberg Forest.

Threats

The primary threats to A. rattrayi are habitat loss and fragmentation resulting from the farming of alien trees. Loss and deterioration of habitat, although occurring relatively slowly (estimated rate of <20% in 30 years), are cause for concern in view of the species’ limited areas of occurrence and occupancy. The fact that the frogs are restricted to small, severely fragmented and relatively isolated sub-populations (sensu IUCN criteria) increases the likelihood of extinction of these sub-populations, and reduces the probability of recolonization.

Recommended conservation actions

Although several of the known sub-populations occur in state forests and nature reserves, it is recommended that additional localities be set aside for long-term protection.

The species was infrequently recorded during the atlas period and additional surveys are needed to gain a better understanding of the species’ distribution and conservation status. Limiting-factor research would aid conservation management planning for this species. Habitat management and monitoring of known populations are also recommended (Harrison et al. 2001).

Forestry companies operating in this area, with indigenous forest under their control, should be informed of the conservation status of A. rattrayi and be advised on how to ameliorate the negative impacts of their activities.

Current distribution map

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