African bullfrogs are found mostly in open grasslands at low elevations in the sub-Saharan African countries of Malawi, Zambia, Nigeria, Somalia, Mozambique, Angola, South Africa (except for the southwestern Cape Province), Kenya, Rhodesia, Tanzania and the Sudan.
African bullfrogs are one of the most adaptable amphibians on earth, capable of tolerating some of Africa’s harshest environments. Certain areas of their range can be completely dry for years at a time, and can reach surface temperatures over 100 degrees Fahrenheit, as well as temperatures that can drop to below freezing during the winter. Protected in an underground estivation chamber, these bullfrogs wait it out until more suitable conditions occur. Once the rainy season begins, these frogs occupy temporary floodplains and ephemeral ponds scattered around the African landscape.
African bullfrogs are carnivorous and will consume nearly any animal that can be overpowered and can fit in their huge mouths. Prey items may include invertebrates, other species of frogs, reptiles, small mammals, and even small birds. Cannibalism is a common occurrence beginning the moment they metamorphose. Many of their first meals will be a member of the same egg mass.
Male African bullfrogs can reach lengths of more than 9 inches and weigh over 2 pounds. With most species of frogs it is the females that are larger but female African bullfrogs are significantly smaller than the males.
During the breeding season, males will congregate in large groups. Much aggression occurs in these groups with larger males pushing, pursuing, biting, and even consuming smaller males. The large males will push their way to the center of the group, establish and defend a small area and begin calling for the females. The call lasts about a second and can be described as a deep low-pitched whoop. The females will hear this call and swim underwater to the center of the group toward the large males while avoiding the smaller males. As they surface in the center of the group amongst the largest males, they are persuaded until finally being seized by a male. Amplexus occurs in shallow water to allow the pair to stand on the bottom. As many as 4000 eggs may be released and the eggs are fertilized above the water’s surface. The males exhibit parental care, a rarity among amphibians. Males will watch over and defend the eggs that hatch. After hatching, the tadpoles will feed on each other, as well as small fish and invertebrates. Defending males will continue to watch over the tadpoles that will metamorphose within three weeks. It’s been observed that during times when the pool they are in nears desiccation, the male will dig a channel between his offspring and a nearby body of water. This parental care comes with a price; however, as the male will consume many of the tadpoles while he is defending them.
In addition to the behaviors associated with reproduction, African bullfrogs show other interesting behaviors, including behaviors that help them survive periods of drought. These frogs have a short active period depending on the rainy season. The majority of their lives are spent estivating underground to avoid desiccation (dehydration). Adults will burrow underground using the metatarsal tubercle on their powerful hind legs. Juveniles lack this tubercle and must resort to utilizing an existing burrow made by some other animal. They slough off several layers of their skin’s epidermal cells that form a tough cocoon. During this time most of their bodily functions slow or completely shut down. This period of dormancy may last a year or more. During the rainy season frogs will sit partially buried with their nose exposed, taking advantage of any smaller animal unfortunate enough to pass by.
No special legal status has been given to Pyxicephalus species. In certain parts of its range, advancing civilization has driven these bullfrogs to near extinction.
Davidson, B. 2000. “Pyxicephalus adspersus” (On-line), Animal Diversity Web. Accessed January 06, 2007 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Pyxicephalus_adspersus.html.