Family Rhacophoridae

Chiromantis xerampelina Peters, 1854

Southern Foam Nest Frog, Foam Nest Frog, Gray Tree Frog, Groot Grys Skuimnespadda (A), Suider Skuimnespadda (A)

By R.C. Boycott and J. Theron

Currently accepted name: Chiromantis xerampelina Peters, 1854
Red listing status: Least Concern (2013)

Photo by Beneke Marita, 2012. URL: FrogMAP: 534

Distribution

C. xerampelina is widely distributed in eastern and southern Africa. In the atlas region it ranges from Mafikeng (2525DC) in the North West Province, eastward through most of Limpopo Province and southward through the eastern lowveld of Mpumalanga and Swaziland to Empangeni (2831DD) in KwaZulu-Natal. In South Africa, the species occurs from near sea level in KwaZulu-Natal (Lambiris 1989a) to 1200 m in the former Transvaal (Jacobsen 1989).

Habitat

The species inhabits a variety of bushveld vegetation types in the Savanna Biome. Breeding usually takes place in temporary pans and vleis, but also occurs in more permanent water bodies such as dams and quarries. In the absence of trees and shrubs, nests may be attached to the sides of large rocks or man-made structures overhanging water, including bridges, culverts and bird hides.

Life history

In summer, these frogs are often seen perched on the branches of trees overhanging or near water, and their white, crusty nests, c.20 cm in diameter, are conspicuous around dams, pans and vleis and along river and stream courses.

In the winter months, they seek shelter under the bark of trees, in rock cracks and on the branches of shady evergreen trees far from the nearest water. They also move into buildings where they take up residence for weeks, or even months, on rafters, walls and windowsills, or behind bookcases and picture frames.

C. xerampelina is adapted in several ways to survive in an arid environment. It possesses a rough, dry skin, and conserves water by means of rectal water re-absorption and by excreting nitrogenous waste in the form of uric acid (Coe 1974). Inactive individuals may be found perched in exposed positions on branches of trees and shrubs where their colour becomes chalky white or pale grey to reflect light and heat.

The males gather at suitable nesting sites at night where they produce soft, discordant croaks and squeaks. They do not appear to be territorial, and two or more frogs close together, or even on top of each other, will call irregularly and independently.

The female leaves the water and climbs up to the nesting site where amplexus with one of the males takes place. Nest construction begins when the female releases an oviducal secretion from her cloaca and churns it into a white foam with her hind legs. Peripheral males take up positions on either side of the amplexing pair and attempt to position their cloacae adjacent to that of the female during bouts of oviposition. Thus the female’s eggs are fertilized by more than one male (Jennions et al. 1992). Neither the amplexing male nor the peripheral males participate in the construction of the foam nest.

The nest may take up to seven hours to complete, and nest construction is split into 2–4 sessions. Between sessions, the female leaves the nest site and returns to the water to rehydrate. At this time, the amplexing male may dismount and, on returning to the nest, the female may amplex with a different male (Jennions et al. 1992). Communal nests, involving two or more females and numerous males, are commonly formed. One such nest contained 50 males and 20 females (Passmore and Carruthers 1995). The female usually returns the following night and adds a second layer of foam (not eggs) to the top of the nest. Males seldom attempt amplexus on the second night; if they do, they soon release the female and leave (M.D. Jennions pers. comm.).

Jennions et al. (1992) recorded a mean clutch size of c.1200 eggs for single-female nests. Once the eggs hatch within the nest, the tadpoles rely on bubbles in the foam for oxygen (Seymour and Loveridge 1994). After 4–6 days, the wriggling tadpoles begin to move downward within the nest, sometimes in a wet squirming mass of several tadpoles or in ones and twos, until they reach the bottom (Wager 1986). It is thought that these movements and the accumulation of tadpoles at the bottom of the nest softens the crust, thereby enabling the tadpoles to drop into the water below where they complete their development. Egg development within a foam nest may serve to avoid or reduce predation in the early stages of tadpole development. However, in some cases, the water below the nest recedes, and the tadpoles drop onto the ground and perish.

Chiromantis xerampelina is preyed upon by arboreal snakes such as the Vine Snake Thelotornis capensis and Boomslang Dispholidus typus. The eggs are eaten by Samango Monkeys Cercopithecus mitis (Rödel et al. 2002) and the Greater Leaf-folding Frog Afrixalus fornasinii (Drewes and Altig 1996).

Conservation

This widespread species is not threatened. Much of the natural habitat of C. xerampelina is used for game or stock farming and it occurs in numerous private and public protected areas.

Current distribution map

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