Written and Photographed by Alex Jordan
Passing on genetic material is ultimately the goal of any organism in the natural world. However, parenting and raising of young is a time consuming effort. Mothers of all species will do whatever it takes to ensure their offspring reach adulthood and hopefully continue their genetic line. When it comes to the world of birds there are a few species that raise their young in a unique and interesting manner. One of the better known families being the cuckoos.
Cuckoos have an ingenious way of conserving energy; allowing their offspring to be raised by another bird species. Instead of building their own nests, cuckoos will lay their eggs in the nest of another bird species. Some species of cuckoo are very specific in the hosts they parasitise, whiles others make use of multiple species. Some species of cuckoo will remove one of the host’s eggs before laying their own in the clutch, and some will simply deposit their egg amongst those of the hosts, allowing the host to incubate them until they hatch.
For the most part, birds need to sit on their eggs in order to incubate them to allow for chick development before hatching, yet cuckoo females are able to hold their eggs internally for a longer period of time before being laid, thus incubation of the eggs will begin within the bird. After the egg has been laid in the nest of the host, the host will further incubate the cuckoo’s egg(s) and they will ultimately hatch sooner than the host birds eggs as they have had a head start through internal incubation. As a result, the cuckoo chicks will outcompete the host’s young for food which will ultimately result in both the death of the host’s young and the far more likely survival of the cuckoo.
A particular relationship of brood parasitism that I was fortunate to witness over the summer at Londolozi was that of the Great Spotted Cuckoo and Burchell’s starling.
Both these birds are the largest of their families, with eggs of similar size and shape. Birds, like most animals, will chase away or warn of any threat that approaches its nest or offspring. A male cuckoo will distract the starling who will leave its nest to chase away the threat. This leaves the nest open and the female cuckoo quickly flies into the Starlings nest (often in cavities of dead trees) and lays its egg. The window of opportunity to lay such an egg is very short and therefore cuckoos are able to lay an egg in a matter of seconds. The cuckoo’s chick will then be raised by the starling who views the cuckoo as that of its own. It’s a bizarre concept to see a bird (that resembles nothing of its foster mother) being fed by another species that has devoted its time and energy into raising its “thought-to-be” young.
Young cuckoos are pre-programmed when they hatch and rely on instinctive traits, that being of migratory patterns, cuckoo recognition, call identification, food and ultimately one day that of host identification for egg laying. A case of nature not nurture. Cuckoo chicks are fed an array of different insects when young but as they mature and fend for themselves they thrive on a caterpillar-specific diet.
This is an unbelievable relationship of nature. Why waste the time building a nest, incubating, feeding and nurturing your young when there’s a way of allowing others to do it? Laying a few eggs in different nests also ensures a greater chance of chick survival and therefore passing on of genes which plays on the saying of “do not put all your eggs in one basket”.
The above relationship shows that there is always something new and exciting to witness and to be learnt in this ever changing environment.