Colours of Wildlife: Cape Rockjumper
Created | Updated Sep 29, 2019
Cape Rockjumper
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
This week I have a very special South African bird for you, a Cape Rockjumper, Chaetops frenatus. What is interesting about it, is that it has no close relatives except one, the Orange-Breasted Rockjumper, Chaetops aurantius, with which it shares a family that only occurs in South Africa. There is just one other entire bird family that is restricted to Southern Africa, the sugarbird family, which also has only two members that are closely related to each other but to nothing else. The sugarbirds occur outside South Africa itself, in eastern Zimbabwe; the rockjumpers occur only inside the borders of South Africa, including in the country of Lesotho which you may know lies inside of ours.
What, exactly, is meant by a bird 'family'? The family as used here, is a unit of classification, and classification today is based on genetic relationships. So birds of a particular family are more closely related to each other than to any birds falling in different families. But the family itself includes groups, called genera (singular 'genus', and also the root of words like 'general'). Most bird families contain many genera – dozens, in the case of bid families as are found among the songbirds. And each genus, itself, contains groups, which we call species. A species is a group of animals that are very closely related, and also treat each other as kin. Animals inside a species breed with each other, but won't ordinarily breed with other species, even ones of the same genus. In the dog family, for example, the genus Canis includes species such as the Grey Wolf, Canis lupus, the Coyote, Canis latrans, the widespread Black-backed Jackal of Africa, Canis mesomelas, and several others.
So any family found to contain only a single genus, and two species, is something quite rare. In the evolution of the Earth's biodiversity, any species that still exists today, comes from a long, long line of ancestors. Since evolution can, and typically does, proceed into every direction that is open, no 'line' of ancestry of anything is just a simple line. There is indeed a main line, which ends up in that particular species, but that line will have many many other branches going into different directions. So when you get a group like the rockjumpers, with but two present species, you can be sure that in the past the group was represented by many other species, that for some reason have vanished. Rockjumpers are therefore the last in line of a group of African birds that were more numerous and diverse in their heyday.
Rockjumpers have long been recognized as unusual birds. Ornithologists have puzzled about where to classify them, and they've at times been considered to be members of the Thrush family, and at other times to be relatives of babblers. Babblers have in the meantime been recognized as no simple family, but actually as birds belonging to several different families. Today, the rockjumpers are considered as being close relatives of another African bird family, itself with only two members, the Picathartes.
The Cape Rockjumper occurs in the Western and a small part of the Eastern Cape Provinces of South Africa. It likes rocky terrain, and the vegetation type called 'fynbos'. This vegetation is mostly a dense growth of woody shrubs with hard, leathery leaves, adapted to the winter rainfall regimen of the southwestern tip of Africa. It is one of the types of vegetation that is most rich in species diversity in the world. In this habitat, rock jumpers like the moister, cooler, high-lying regions, but can be found down to sea level in some places. The rockjumpers are alert, wary birds. They're about the size of a thrush, reaching 25 cm/10" in total length. They are usually found in pairs or in small groups. The painting I've made is of the male; the female is duller, without the rich reddish underparts and bold black markings of the face, neck and breast of the male. Rockjumpers don't fly much, instead bounding powerfully from one rock to the next. They fly only when startled or disturbed, or when there's a long distance to the next rock. Peering into crannies between rocks, they seek the small critters they prey on: insects, and, sometimes, small lizards like geckoes. They will sometimes scratch and dig in the soil and leaf litter.
Most of the time, rockjumpers can be located by their calls. They have a variety of territorial, alarm and contact calls, the most typical being a 'pee-pee-pee-pee' that gradually falls in pitch. When they feel threatened, they'll dive behind a rock or tuft of grass, and then reappear a distance off.
For rockjumpers, breeding season is in the spring. Since the region where it occurs has winter rainfall, this time would be after the rains have ended, but many of the plants of the region will still be growing from accumulated water and nutrients. I wasn't able to find any information about their courtship behaviour. They make their nests on the ground, beside or beneath rocks and hidden by tufts of grass or other vegetation. The nest is a cup woven with coarse grass, rushes or restios (rush-like plants of the fynbos), and sticks, decorated with mosses and lichens. The bowl is lined with fine plant fibers or hair. The female lays two or three, rarely four, eggs. Both sexes incubate, and sometimes there is even a 'helper', usually male, perhaps an offspring of the pair from a previous season.
There is much we still don't know about this unique species. At present, though they have very specific habitat requirements and a fairly small range, they're not considered threatened. They need watching, though, as patches of their habitat are still being lost to human development and encroachment by alien tree and shrub species.
