Image from Milan Zygmunt 500px
The most wonderful sound to wake up to - the call of a Bullfrog (Pyxicephalus adspersus) at my pond! I haven’t heard one for years, so I immediately jumped out of bed (at 1am!), grabbed the torch and rushed to the pond. It took me quite a while to find him - first of all he heard me, so kept quiet for a while, but then continued - and secondly the torch light was rather dim. But eventually I found him. There he was! Cleverly hidden under a large rock in the shallows. I did have my camera with me, but the pics showed nothing in the darkness. So I looked for him the next morning and did find him (I in fact found two), but he was not nearby the size of the pics below - a youngster, about 10cm (4”) long and the minute he saw me, he left the safety of the rock he was hiding under and swam to deeper waters. So once again, no pic. It’s hard to believe that such a small chap can have such a booming voice!
The large rock (top right) under which he was hiding
Their loud booming calls (to attract a female) can be heard for miles and the first time you hear it (for me it was in the early 80’s at my previous wildlife pond), you’re not sure whether to investigate or to flee!
This species occurs widely in South Africa, Swaziland, Namibia, Botswana, and Zimbabwe, extending north to southern Angola, Zambia, Malawi, Mozambique, Tanzania, and Kenya. One of the most adaptable amphibians on earth, Pyxicephalus can tolerate some of the harshest environments in Africa. Certain areas of their range can be completely dry for years at a time, and can reach surface temperatures over 100 degrees F, and drop to below freezing during the winter. Protected in an underground estivation chamber, the frogs wait it out until more suitable conditions occur. When the rainy season begins (usually November), they come out of their chamber, occupy temporary floodplains and rapidly drying puddles scattered around the African countryside, just for a few short days or a couple of weeks.
I am totally thrilled that they have taken up residence in my garden!
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Image from BioLib
It is the largest amphibian found in southern Africa. Males can reach a snout-vent length of 24,5 cm and a mass of 1.4 kg
It is common in many of the southern parts of its range, it has apparently declined in South Africa, especially in Gauteng Province, but it is still locally common in some places. Boycott (2001) declared the species to be extinct in Swaziland. It seems to be very uncommon in the northern parts of its range, with very few confirmed records from Zambia, Malawi, Tanzania and Kenya (though this might in part be due to identification problems)..
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Male Pyxicephalus adspersus can reach lengths of more than 9 inches and weigh over 2 pounds. Females are much smaller. Males are olive in colour, with yellow to orange on the throat region. Females are olive to light brown with cream to white throat areas. Both sexes have ridges running laterally on the dorsal surface. Juveniles are much more colourful than adults. Several white to yellow lines run down the animal's dorsal area on an overall mottled background. Both these dorsal lines, and mottling disappear with age. Adults have a spade like metatarsal tubercle on each hind foot to aid in digging. The front toes are thick and blunt with no webbing, the rear toes are slightly webbed. These frogs have massive skeletons with extremely large, heavy skulls. The bottom jaw has three odontodes which act as huge teeth, and are used in restraining struggling prey.
During the breeding season, males will congregate in large groups. Much aggression occurs in these groups with larger males pushing, pursuing, biting, even consuming smaller males. The large males will push their way to the centre of the group, establish and defend a small area and begin calling. 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 centre of the group, to avoid the smaller males and surface in the defended area of a larger male. As they surface, they are persuaded until finally being seized by a male. Amplexus occurs in shallow water to allow the pair to stand on the bottom. Eggs are fertilized above the water's surface. As many as 4000 eggs may be released. The males exhibit parental care. Males will watch over and defend the eggs which hatch in two days. After hatching, the tadpoles will feed on each other, as well as on small fish and invertebrates. Defending males will continue to watch over the tadpoles which will metamorphose within three weeks.
Behavior
These frogs have a short active period depending on the rainy season. The majority of their lives are spent estivating underground. Adults will burrow underground using the metatarsal tubercle on their powerful hind legs. Juveniles lack this tubercle and must resort to utilising an existing burrow made by some other animal. They slough off several layers of their skin's epidermal cells which form a tough cocoon. Most of their bodily functions slow or shut down all together. This period of dormancy may last a year or more. During the rainy season frogs will sit partially buried with the nose exposed, taking advantage of any smaller animal unfortunate enough to pass by
Food Habits
Pyxicephalus adspersus is carnivorous and will consume nearly any animal that can be overpowered and can fit in their huge mouths. Cannibalism is a common occurrence beginning the moment they metamorphose. Many of their first meals will be a member of the same egg mass. Other prey items may include invertebrates, other species of frogs, reptiles, small mammals, and even small birds. The tongue is folded over inside the mouth. To capture a potential meal, it will drop its lower jaw with considerable force, causing the tongue to flip over and out of the animal's mouth, seizing the prey
Did you know?
Certain areas of their range can be completely dry for years at a time, and can reach surface temperatures over 38 degrees C, and drop to below freezing during the winter. Protected in an underground estivation chamber, the frogs wait it out until more suitable conditions occur. In fact, the majority of their lives are spent estivating underground. They slough off several layers of their skin's epidermal cells which form a tough cocoon, which prevents the evaporation of body fluids. Most of their bodily functions slow or shut down all together. They absorb water stored in their bladder. This period of dormancy may last a year or more. When the rainy season begins, they occupy temporary floodplains and rapidly drying puddles scattered around the African countryside.Males have two breeding strategies, depending on their age: Younger males congregate in a small area, perhaps only 1 or 2 square meters of shallow water. The larger males occupy the centre of these breeding arenas or leks and attempt to chase off other males. In fact they fight, causing injury and even killing one another. The dominant male attempt to prevent other males from participating in breeding. A female approaches the group of males by swimming along at the surface until she is within a few meters of the group. Then the female dives to avoid the smaller males and surfaces in the defended area of a larger male in the middle of the group. She is soon grasped by one of the larger males, and mating ensures. Most of the females are mated by the dominant male in his territory.
The major threat through most of its range is harvesting of frogs for local consumption, which is believed to be responsible for some population declines. In South Africa, breeding habitat has been lost due to urbanisation. This species is sometimes found in the international pet trade but at levels that do not currently constitute a major threat.
Economic Importance for Humans: Positive
African bullfrogs are eaten by humans, and have been collected for the commercial pet trade.
Economic Importance for Humans: Negative
Because these frogs are such resilient animals, they might potentially have negative effects on the surrounding ecosystem if introduced by humans beyond their natural range.
Listed as Least Concern because, although it is losing breeding habitat in places due to urbanisation, and it is also eaten in parts of its range, it has a wide distribution, is tolerant of a broad range of habitats and has a presumed large population.
(Much of this info from Animal Diversity Web)
NZG details :
Tel: +27 12 328 3265, Fax: +27 12 323 4540 | 232 Boom St, Box 754, Pretoria, 0001, South Africa.
At last somebody is doing something about our declining amphibian population! Thank you NZG!
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Brilliant. It is so rewarding when wildlife chooses our gardens as a natural living and breeding spot.
ReplyDeleteI know John, I'm always ecstatic when somebody new moves in! Thanks for stopping by!
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