"Piet-my-vrou, Dee-dee-d-d-d, Maykie, I’m so sad” – these are some of most common bird calls that one hears during the summer months in southern Africa throughout a variety of habitats and environments.
These characteristic calls belong to some of the cuckoo species which migrate south of the Equator during our summer months, which range from November to April. Apart from their melodious calls, these birds are often brilliantly coloured (as with the iridescent Diderick’s cuckoo), they undertake impressive migration flights – but what makes them really interesting is their breeding behaviour and tactics…southern African cuckoos are obligate brood parasites – meaning that they lay their eggs in other birds’ nests, as this is essential to their survival.
Ten cuckoo species breed in southern Africa. While most cuckoos parasitize a number of different host species, a few are host specific and have only one host. Host species include robin-chats, shrikes, starlings, babblers, bulbuls, warblers, sunbirds, weavers and wagtails.
In order for cuckoos to maximise their gain by laying their eggs in ‘surrogate nests’, they have evolved devious and cunning tactics in order to fool their suspicious hosts into rearing their young:
• In order to carry out their deceptive plan, cuckoo pairs will often work together, the male distracting the host from the nest while the female nips in to add her egg to the clutch.
• Cuckoos are able to lay their eggs in a matter of seconds, decreasing the chances of being caught by the host.
• Cuckoos can closely mimic the eggs of the host, in both size and colour – making it near impossible for the host to discern them from their own.
• Cuckoo eggs are often thicker shelled and more resistant to cracking than the host eggs.
• Cuckoo eggs require a shorter incubation period than the host eggs…ultimately giving the parasitic chick a head start in life. This is because the embryo actually starts to develop while the egg is still inside the female, unlike most other species that only start to develop once the egg is laid and is incubated.
• Some adult cuckoos are known to push the host eggs out of the nest and even trample any hatchlings if present. Generally the cuckoo will remove only one egg and replace it with its own.
• Cuckoo hatchlings will often instinctively push the hosts un-hatched eggs or chicks out of the nest.
• Besides egg mimicry, cuckoo chicks are capable of mimicking the host chick’s plumage.
• Cuckoo chicks develop rapidly and often out-compete any remaining host chicks.
• Some cuckoo species will lay many eggs during a breeding season and will have a number of host species. A great example of this is the Klaas’s cuckoo, which has up to 24 host species.
One can see that cuckoos have put in a huge effort into deceiving their hosts, so surely there must be advantages to this behaviour…there definitely are:
By not having to invest substantial amounts of time and energy in nest building, incubating and rearing their own young, enables the adult cuckoo to focus all their energy into laying more eggs. By lying one egg per host nest and not putting all their eggs into one nest, the survival rates of the offspring are greatly improved.
This is a great example of Darwin’s theory of evolution by means of natural selection…basically ensuring species survival by staying one step ahead of the game.
Images by Caroline Culbert, Martin Benadie and Warren Ozorio