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Description
This is a medium sized toad. The parotid glands have numerous prominent warts, and the toads have numerous subdigital tubercles. They often have a light vertebral stripe, but never have red coloration on outer parts of the thighs.
This toad has very warty skin. Adult males measure 38–54 mm (SVL), females 41–60 mm. They contain one marked protruding bulge above each eye. The large tympanum reaches 0.6–0.9 of eye diameter, and is surrounded by a narrow bony circle. Parotid glands are well-defined, yet rather flat and elongate with parallel borders and numerous prominent warts. Males have single subgular vocal sacs, enlarged thenar tubercles and black nuptial pads on the outer faces of the first and second fingers. Those on the second fingers are sometimes vaguely defined. The horny tips of the warts are quite thorny on males, but rather blunt on females. The large inner metatarsal tubercle reaches 0.5–0.7 of the length of the shortest toe. Subdigital tubercles are numerous and invariably well-defined.
Perret (1966) mentions nuptial pads arranged on the first three digits of males. The specimens measured by the same author and by Mertens (1938b), Loveridge (1941), Perret & Mertens (1957b), Perret & Amiet (1971), Lamotte & Xavier (1981), Wager (1986), Poynton & Broadley (1988), Lambiris (1988) and Poynton & Haacke (1993) were larger than the animals which I have examined personally. They give 45–60 mm SVL for males, and 53–85 mm SVL for females. According to Hulselmans (1970), the specimens, reported by Parker (1963c) are actually B. maculatus. However, these have a tympanum size of just 0.5 of the eye diameter. The short parotid glands are separated from the eye by a distance which corresponds to 0.5 of the eyelid.
Voucher specimens: SMNS 8946 1–12 + tadpoles; SMF 78626–27.
Coloration: The color of this toad is highly variable. Apart from uniform brown animals there are, rarely, completely yellow individuals. The markings on the extremities of these specimens are paler, almost white. In this case, the warts bear very well-defined black dots. Most individuals show a light, often yellow, vertebral stripe starting roughly at the anterior border of the eyes and covering at least 2/3 of the back, or it stretches to the end of the body. Many specimens have some dark dorsal patches which are arranged almost symmetrically. However, these are less well-defined than those of the two following species. Dark transverse bars usually appear on the upper lips and on the extremities. The flanks are often brighter colored than the back. Darker specimen often have large yellow warts on the flanks. Yellow warts may also appear on other parts of the body, especially on the thighs. The finger tips are usually white. The venter and the inner sides of the limbs are white to gray. The throat of the males is black with numerous scattered white or yellow spots. The residuary webbing may be pale gray to deep black. The border of the eye is yellow or brown, and the iris golden or silverish. The coloration of preserved animals almost corresponds to that of living individuals. However, the brown colors appear somewhat paler, and the markings are less well-defined. Very rarely, the parotid glands are smoother than those of living toads.
Joger (1981) reports on light colored specimens from eastern Nigeria showing almost no markings. Tandy & Keith (1972) describe yellow-green males of B. kisoloensis and B.lönnbergi. According to Channing & Drewes (1997), Bufo kisoloensis males are yellow during breeding season, but otherwise cryptic colored.]
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Benin, Cameroon, Cote d'Ivoire, Ghana, Mozambique, Nigeria, Senegal, Sierra Leone
This toad is found in humid savannas of West and East Africa, stretching southwards to north-eastern South Africa. In West Africa, this species probably inhabits the areas covered, now and previously, by rainforest, but it colonizes large parts of the savanna along the rivers. In particular, the species has been recorded from the following countries: Guinea, Liberia, Sierra Leone, Burkina Faso, Ivory Coast, Ghana, Benin, Nigeria, Cameroon, Congo, R.D. Congo, Central African Republic, Ethiopia, Uganda, Tanzania, Malawi, Zambia, Botswana, Zimbabwe, Mozambique, South Africa, Namibia, Angola (Nieden 1908, 1910b, Barbour 1911, Chabanaud 1921, Noble 1924, Parker 1936c, Mertens 1940, Loveridge 1941, Paulian & Vilardebo 1946, Romer 1953, Perret & Mertens 1957, Taylor & Weyer 1958, Laurent 1961b, 1972c, Perret 1966, 1977a, Poynton 1966, 1991, Stewart & Wilson 1966, Stewart 1967, Amiet & Perret 1969, Perret & Amiet 1971, Hulselmans 1970, 1978, Broadley 1971, Channing 1972, 1989, Amiet 1973a, 1975, 1976a, Stevens 1974, Böhme 1975, 1994c, Joger 1981, 1982, 1990, Barbault 1984, Wager 1986, Böhme & Schneider 1987, Zug 1987, Branch 1988, Hughes 1988, Lambiris 1988, Poynton & Broadley 1988, Böhme & Nikolaus 1989, Largen & Dowsett-Lemaire 1991, Channing & Griffin 1993, Poynton & Haacke 1993, Simbotwe & Mubemba 1993, Passmore & Carruthers 1995, Böhme et al. 1996, Rödel 1996, 1998b, Joger & Lambert 1997, Largen 1998).
At Comoé National Park, this toad is found along rivers, in the forests and in the savannas. In general, the species is often associated with both forest (Perret 1966, Amiet 1976a, Joger 1981, Böhme 1994c) and savanna habitats (Amiet 1975, Joger 1981, Böhme & Schneider 1987, Hughes 1988); in the latter case, it is often considered as a gallery forest-dweller (Amiet 1976a, Böhme et al. 1996). According to Poynton & Broadley (1988), it is a savanna species.
Life History, Abundance, Activity, and Special Behaviors
Spawn: Two egg strings are simultaneously discharged from the cloaca of the female. The eggs, with their black and white poles, are first situated rather close to each other, but when the jelly has swollen, they are situated at alternating intervals. At this stage, the diameter of the egg is 1.5 mm. Altogether, both egg strings may comprise 2000 to 8000 eggs. The tadpoles usually hatch after two days.
At Lamto, females laid on average 4809 + 1892 eggs with a diameter of 1.3 mm (Barrault 1987). According to Tandy & Keith (1987), all African Bufo species produce two egg strings. Wager (1986) reports on eggs with a diameter of 1.2 mm forming a single row within a jelly tube of 3 mm width.
Tadpoles: Immediately after hatching, the tadpoles still possess external gills and paired ventral adhesive organs by means of which they are connected to the jelly. Two days later, they measure 2.5 mm BL (TL: 7 mm). Later on, the coloration of the rather compact tadpoles (TL= 2.3–2.4 x BL) corresponds to that of the substrate, being brown to usually deep black. Viewed from above, the body appears slightly constricted on both sides, on the level of the unpaired spiracle situated on the left. The body is covered by a transparent layer, and the short muscular tail axis bears an almost symmetrical tail fin that shows no markings. The tail fin inserts at the level with the tail base. The eyes are arranged laterally, but almost on the top of the head. The nostrils are situated dorsally and hardly visible when the tadpoles are viewed laterally. The slender horny beaks are serrated, and the oral disc is lined with a single row of papillae on both sides. The keratodont formula of fully developed larvae is 1 / 1+1 // 3 or 1 / 1+1 // 1+1 / 2. The elongate keratodonts are 3 to 3.8 times longer than wide. Their distal tip bears blunt apical and lateral points. Laterally, the latter approximately cover 1/4 to 1/3 of the total tooth length.
In captivity, the hind limbs developed within one month, and metamorphosis took place about two weeks later. In the wild, this process takes up far less time, and some individuals even metamorphose within two weeks. The largest larvae ever found measured 18 mm, weighing about 0.04 g. SVL of freshly metamorphosed toads is 6.5–7.5 mm.
Channing’s (1972) description of Bufo pusillus is very similar to West African tadpoles of B. maculatus. We however did not observe a counter-shaded tail axis in our specimens. Lambiris (1989) describes a typical Bufo tadpole which he terms B.pusillus, showing the keratodont formula 1 / 1 + 1 // 4. These tadpoles have a single lateral row of papillae with considerable gaps, frontad and caudad of the oral disc. They reach a TL of 17 mm. According to Perret (1966), the larval development of B. maculatus corresponds to that of B. regularis.
Spawning B. maculatus can be encountered at Comoé National Park all over the year. In West Africa, breeding couples were found by Joger (1981) even during the dry season when the males call during the night on the river banks. Stewart (1967) reports that a breeding period at Malawi lasted throughout the rainy season. According to Channing (1989) male’s calling activity was especially high during a dry spell at the end of January in Namibia. To guarantee acoustic separation, they occupy sites far away from each other, a phenomenon which was also noted by Tandy & Keith (1972). However, a more recent study failed to show spacing patterns in calling males in Comoé National Park (H. Lüssow, pers. comm.). Males start calling at nightfall. A second calling peak was regularly registered at dawn. In the dry and early rainy season, calling males will normally be encountered in shallow water where they hide under flat stones, in crevices or under dead wood. In Namibia, Channing & Griffin (1993) recorded males calling from the water’s edge, well concealed under vegetation.
The pairs breed in small and shallow inlets and puddles created by the rising and falling river. The animals also often make use of rock-pools. The egg strings are either wound around stones or twigs or simply deposited on the gravely or sandy substrate. Calling activity is far more considerable during long dry periods than during or shortly after rainfall (for a contradicting statement see Spieler & Linsenmaier 1999a). This observation appears quite logical on the assumption that the water level will rise after rainfall, enabling various fishes to colonize those ponds which had thus far remained isolated. These predators are likely to decimate the toad tadpoles in no time. As a protective strategy, the tadpoles aggregate in the border zone of their puddles. There they create small hollows in the sand by their collective body movements. The factors triggering these aggregations have been examined in detail by Spieler (1997b) and Spieler & Linsenmaier (1999a). They found that a combination of two stimuli caused this behavior: a chemical cue from injured tadpoles and a mechanical stimulus caused by rapid movements of aquatic predators. Aggregated tadpoles faced slower growth and increased risk of desiccation. Aggregations broke up within 24 hours after predators had left the spawning sites. Occasionally toad tadpoles, together with potential predators, are found in small residuary ponds without showing any tendency to aggregate. It is uncertain whether these tadpoles are B. regularis. Balinsky (1969) reports on South African B. regularis (= B. gutturalis ?), whose calling activity was also negatively influenced by rainfall.
As soon as the rainy season begins, the behavior of the toads changes completely. Most of them leave the river banks to forage for prey in the gallery forest, or form new breeding choruses in the savanna. While I sometimes heard calling males near forest ponds, I never found eggs or tadpoles at these sites. In the savanna, choruses may originate at any type of water, but at a given time, they always concentrate on a restricted number of ponds. Most choruses are found along periodic brooks. Most probably, the latter also serve as landmarks by which the toads orient themselves during their excursions across the open savanna. During the day, calling males are found exclusively at lotic brooks. During the rainy season, the toads call either on the banks or, clung to blades of grass, in the middle of fast-running brooks. I rarely observed calling males floating at the surface.
Voice: The snoring call lasts approx. 0.9 sec, and is composed of numerous almost equal pulses lasting 0.03 sec each (frequency: 0.7 to 5.5 kHz). It is usually repeated in rapid succession, the shortest interval between two calls being 0.53 sec. Quite regularly, males will call alternately. Schiøtz (1964) has published a sonagram of this species, which he recorded from B. regularis. The "deep roar" lasted 0.55 sec. The dominant frequencies were 0.4 and 1.1kHz. According to Amiet (1976a), a complete sequence of calls lasts about 7–10 sec. This author mentions a dominant frequency of 1.5–2 kHz.
In savanna pools, the chances of survival are apparently even slimmer than in river bank habitats. For example, just 74 freshly hatched tadpoles of Hoplobatrachus occipitalis succeeded in consuming all the toad tadpoles (approx. 2000) inhabiting the respective pond (ca. 220 l) within three days. I never observed aggregations of toad tadpoles in savanna pools although predators were invariably present. This makes sense as in contrast to the puddles along the rivers, predators will not leave the ponds, even when the water level goes down. In such an environment a stationary aggregation would be an excellent and easily-exploited food source for any predator.
Unless heavy rainfall occurs, toads are virtually nocturnal animals the entire year. Apart from breeding individuals, they are found nearly exclusively in the forest. Once a day refuge has been chosen, it is used over a long period of time. Each hut of our research camp had its own "domestic toad" which often proved to use the same refuge for months. Day refuges included small holes in the soil, between the roots of trees, under rotten wood or in rock crevices.
Insects attracted by open light, mainly termites, invariably catch the interest of toads. According to Paulian & Vilardebo (1946), ants and beetles form the bulk of their diet; these authors especially refer to the big African stink ant Paltothyreus tarsatus. Mertens (1938b) also mentions ants as a preferred prey. In Zimbabwe, this toad is said to differ from B. gutturalis, which replaces B. regularis in that region, by its preference for smaller prey, different microhabitats and different breeding periods (Lambiris 1989). In Comoé National Park B. maculatus e.g. is predated on by the snake Causus maculatus (pers obs.) and by the scorpion Pandinus imperator (D. Mahsberg, pers. comm.)
Comments
This account was taken from Rödel, M.-O. (2000), Herpetofauna of West Africa vol. I. Amphibians of the West African Savanna, with kind permission from Edition Chimaira publishers, Frankfurt am Main.
For references in the text, see here
References
Rödel, M. O. (2000). Herpetofauna of West Africa, Vol. I. Amphibians of the West African Savanna. Edition Chimaira, Frankfurt, Germany.
Originally submitted by: Marc-Oliver Rödel (first posted 2001-02-21)
Edited by: Vance T. Vredenburg (2015-05-18)Species Account Citation: AmphibiaWeb 2015 Sclerophrys maculata: Flat-backed Toad <https://amphibiaweb.org/species/227> University of California, Berkeley, CA, USA. Accessed Dec 21, 2024.
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Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 21 Dec 2024.
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