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!"
Today's painting is of an African Cuckoo, Cuculus gularis. Once more the name isn't very appropriate. There are many, many other cuckoo species in Africa, and this one isn't even remotely the commonest one of them! It is, however, closely related to what is called the 'Common' or Eurasian Cuckoo, Cuculus canorus. Which, by the way, also occurs in Africa. The difference is that the African Cuckoo is a breeding intra–African migrant (in other words, it migrates around the continent without going outside it), while the Common Cuckoo breeds in Europe and Asia and is a non–breeding migrant to Africa.
Here is a very informative site about a recent project mapping the movements of Common Cuckoos into and out of Africa:
The African Cuckoo looks so similar to the Common Cuckoo that it's almost impossible to distinguish them in the field. The only visible difference is that African Cuckoos have a slightly more pronounced yellow base to the bill, and white barring, rather than spots, on the outer tail. It's about the size of a dove, reaching 33 cm/13" in total length.
But the easiest way to distinguish them is by their call. Common Cuckoos don't call while they are in Africa, since they're not breeding. The African Cuckoo does call, and its voice is very similar, but differs in that both notes of the 'coo–coo' call are at exactly the same pitch. The Common Cuckoo has the first note higher than the second; anyone familiar with a cuckoo clock will know that.
Other African cuckoo species have very different calls, but almost all of them are highly distinctive, and many of them – like the name 'cuckoo' itself – have common names mimicking or inspired by their calls.
Like the Common Cuckoo, the African Cuckoo is a brood parasite. That means it doesn't raise its own chicks. Female cuckoos, after mating, lay their eggs in other birds' nests … typically, quite a large number of them – only one egg in each nest, though. Her mate will usually try and distract the intended host parents, and while they're not paying attention, she will sneak in and quickly lay an egg in their nest. She will even push out one of the hosts' eggs at the same time in case they should count the eggs when they return. But she finishes the whole process in only about ten seconds.
Some of the cuckoo eggs are recognized as such by the hosts, but many are not. These are then raised by the 'foster parents' who seem to be oblivious to the fact that the chick is not theirs, no matter how different from them it looks. Cuckoo eggs hatch more quickly than those of the host … in fact it has been discovered that the female cuckoo can keep the egg inside her body for an extra day and give it a 'pre-incubation' to give it a head start. Then when the cuckoo chick hatches it will push the unhatched eggs of the foster parents out of the nest so it will have no competition for their attention. The young cuckoo typically starts out big and becomes even bigger very quickly, eventually dwarfing its 'parents'. In fact in ancient times it was believed the young cuckoo would end up swallowing its foster parents as well! This doesn't really happen. But the cuckoo does eat as much as several of their 'real' children would have. What's more, it makes as much noise as an entire nest full of chicks as well, to stimulate the parents into feeding it full–time!
While the Common Cuckoo has been known to parasitize more than a hundred different species, the host for the African Cuckoo has been quite unknown until recently. It turns out to be the Forktailed Drongo, Dicrurus adsimilis. I will try and paint one of these soon; it is a widespread and common savannah bird in sub-Saharan Africa, but surprisingly poorly known. Drongos are shiny black, noisy songbirds with forked tails, and are expert hunters of flying insects. They, too, are smaller than the cuckoos that parasitize them. We do not know much about their breeding, but what is interesting is that there is a lot of variation in the appearance of drongo eggs. There is similar variation in the appearance of the eggs of the cuckoos that parasitize them. Just as with the Common Cuckoo, in which there are different populations, called 'gentes', each of which parasitizes a particular species and has eggs that closely resemble those of that species, in the African Cuckoo there are different gentes each of which specializes in drongos with eggs of a particular look. This is a very interesting parallel where the same system that the Common Cuckoo uses for many species, is applied by the African Cuckoo to just a single host species. (Just note that is possible that there might be some other host species that we currently don't know about.)
Selective pressures are probably behind this. In any species parasitized by cuckoos, there will be a certain number of the intended foster parents that are able to recognize the cuckoo eggs as not being their own. In this case they may eject the cuckoo egg from the nest, or abandon the nest altogether and make a new one, laying a new batch of egg. The greater the percentage of parents that recognize the eggs, the greater the loss to the cuckoo. While a female cuckoo can lay 50 eggs, each in a different nest, each season, it still would improve her success rate if she could fool more of the intended hosts. So, cuckoos whose eggs look more like those of their hosts will have more babies that survive to breed themselves. Meanwhile the same kind of pressure on the hosts will cause them either to improve their egg discrimination skills, or to develop eggs that vary more in appearance, making the job of exactly matching them harder for the cuckoos. This seems to be what is happening with the drongos. So, both the cuckoos as well as their hosts are now in a kind of evolutionary race. This is one sort of thing that actually drives the entire process of evolution.
This talk of 'parasitism' makes it seem as if cuckoos are bad guys in the bird world. Actually, the way they 'drive' evolution as I explain above might be a valuable contribution, leading to more rapid evolution of new species and ultimately greater biodiversity. The study of how cuckoos select hosts and how they vary the appearance of their eggs is fascinating, and at present we still know very little about it.
Then there's also the fact that cuckoos are ecologically important. Almost all cuckoo species prey on hairy caterpillars (that is to say, butterfly babies) that no other birds would eat. The stinging hairs apparently don't harm the cuckoos, but are rubbed off during the process of digestion until eventually the entire stomach may have a thick lining of stinging hairs! If not preyed upon by the cuckoos, these caterpillars would cause a lot more damage to the foliage of trees and shrubs. Again, the way the ecosystem is set up necessitates that there should be a proper balance between predators and prey. Every species on Earth has its own special role to play.
Apart from the details of its breeding system, we do not know much about African Cuckoos. As I said above, they migrate around Africa, breeding in woodlands and well–wooded savannahs. In South Africa the breeding season is between September and March – our Spring and Summer. Cuckoos can be heard calling during this season, but are hard to see. They will sit and call high up in a tree, well hidden by the leaves, and will stop if you approach them too closely. Their calls seem to be designed to make it hard for you to locate them. Typically they will be farther away than they sound. If you do eventually manage to pinpoint one, unless you are very skilled at sneaking up on it, it will see you and fly off, still hiding as much behind the leaves and trees as it can.
Because of it being so skulking and secretive, I have not yet managed to catch a glimpse of one of these cuckoos in the wild. I have seen its relatives the Red–chested and Black Cuckoos, though, so I will continue to keep an eye out for it.