Breviceps macrops Boulenger, 1907
Original Published Description:
Desert Rain Frog, Melkpadda (Afrikaans), Web-footed Rain Frog (English), Boulenger's Short-headed Frog (English), Blaas-op (Afrikaans), Jan Blom (Afrikaans), Donderpadda (Afrikaans)
This species occurs on the Namaqualand coast of South Africa, north to Lüderitz in coastal south-western Namibia. It ranges from close to the high-water mark to 10km from the coast. B. macrops also occurs in the southern coastal dunes of Namibia, from Lüderitz southward to Oranjemund (Minter et al., 2004, © SI/MAB Biodiversity Program).
From Greek 'macro-,' meaning large, and 'ops' meaning eye.
Females reach up to 50 mm in length (Channing, 2001). The holotype measure 48 mm from snout to vent (Boulenger, 1907).
Head is comparatively larger and body less bulging than in B. gibbosus and allies. The eyes are significantly larger, their diameter 6.5 to 8 times in the length of the head and body. The interorbital space is narrow, barely half the width of the upper eyelid. The tympanum is not visible. Digits are shorter and thicker than in the other species of the genus, and Channing called the hands and feet "paddle-like, with fleshy webbing." First and second fingers are equal, twice as long as the fourth, a little shorter than the third, which is not longer than the eye. Toes are extremely short, increasing in length from the rudimentary first to the fourth, which is not longer than the third finger. The fifth is as long as the second. Subarticular tubercles very small, very feebly prominent under the fingers, and absent under the toes. Two large, feebly prominent metatarsal tubercles are present; the inner is flattened and spadelike and longer than its distance from the extremity of the first toe. Small, smooth warts are present on the dorsum. The limbs and venter are smooth (Boulenger, 1907).
Dorsum is a pale sand-colour with dark brown spots or marblings. A broad, dark angular or curved band is present from one eyelid to the other across the back of the head. A narrow straight dark streak is present across the forehead, between the anterior borders of the upper eyelids. The upper lip, limbs, and venter are white (Boulenger, 1907).
B. macrops is a squat, rotund frog with short limbs and large, prominent eyes. The interorbital distance is about half the horizontal diameter of the eye (Poynton 1964). Fleshy webbing is present between the fingers and toes, and sub-articular tubercles on the fingers are absent or weakly developed (if present, they are single, not double, cf. B. namaquensis). The dorsum is light yellowish-brown, variably marked with fine, dark brown speckles or larger vermiculations that sometimes form a border around a pair of large, light patches in the scapular region. The ventrum is white with a large, central, unpigmented area through which the abdominal muscles, blood vessels and other internal organs can be seen (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).
Habitat and Ecology
It lives in sand dunes vegetated with low, succulent shrubs and other xerophytic vegetation in the fog belt (Minter et al., 2004).
B. macrops is restricted to Strandveld Succulent Karoo, in the Succulent Karoo Biome. It inhabits sand dunes vegetated by low, succulent shrubs and other xerophytes. These plants usually cover the crests of the dunes which are separated by open areas of bare sand. De Villiers (1988c) found that the dunes are mostly formed by white, calcareous sand, but reddish dunes occur at some localities where the species is known to occur, for example, alongside the Holgat River (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).
It is a locally common species (Minter et al., 2004).
Populations of this species are decreasing (Minter et al., 2004).
This species in known to feed on beetles and moths found in dung (Channing, 2001).
Analysis of scats revealed that prey items include beetles and ants (Channing and Van Wyk 1987). While tracking frogs on the surface, Carruthers and Passmore (1978) found signs of activity around dung and suggested that the frogs were feeding on insects attracted to the dung. Haacke (1975) reported the adder, Bitis schneideri, was recorded as a predator at Lüderitz (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).
This species is a direct developer with no morphologically distinct, free-living larval phase; development occurs within the egg membranes and individuals emerge as tiny froglets. Reproduction is not associated with water (Minter et al., 2004).
The call is a heard throughout the year with males calling in the open. Often one male begins calling and others follow in a regular pattern. Channing (2001) described the call as a "subdued rising whistle." The frequency ranges from 1.2-1.4 kHz with the dominant frequency at 1.3 kHz. The call lasts slightly more than 200 ms.
The advertisement call is a single, long, low-pitched whistle. Calls recorded at Port Nolloth had an emphasized frequency of 1200 Hz rising slightly to 1300 Hz. They varied between 1.2 and 2.5 seconds in duration (cf. Channing 2001) and were repeated at relatively long intervals (10 seconds to 15 minutes), depending on the chorus intensity (unpubl. data). The calls were lower in emphasized frequency and much longer than those of B. namaquensis (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).
Calling and/or surface activity has been recorded in almost all months of the year, usually during and following fog. Males call from the surface, sometimes excavating a slight depression in the sand, or moving from one call site to another while foraging (unpubl. data). The distance between calling males may be as little as 1 m, and choruses are apparently organized (Channing 2001). Calling is inhibited by dry, warm weather, but not by low temperatures (S. Hanrahan pers. comm.; pers. obs.). Amplexus, oviposition and development have not been recorded (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).
Activity and Special Behaviors
This is a fossorial species that is active at night. When threatened, it inflates its body and ellicits a shrill scream (Boulenger, 1907).
IUCN Red List Category and Justification of Conservation Status
The IUCN Red List (2009) categorizes this species as Vulnerable because its Area of Occupancy of less than 2,000 km2, its distribution is severely fragmented, and there is a continuing decline in the extent and quality of its habitat, area of occupancy, number of locations, and number of mature individuals (Minter et al., 2004).
B. macrops was previously listed as Restricted (Branch 1988), Vulnerable (IUCN 2000) and Near Threatened (Harrison et al. 2001). B. macrops does not occur within a protected area. The species is protected in terms of the Cape Nature Conservation Ordinance 19 of 1974 (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).
The main threat to the species is loss of its habitat as a result of coastal opencast diamond mining. Development of roads, increasing pressure from human settlement, and changing land-use (e.g. increased grazing) pose additional threats (Minter et al., 2004).
Conservation Actions and Management
It is not known from any protected areas; conservation areas are needed within the range of the species (Minter et al., 2004).