Introduction

An African Cuckoo fledgling, almost ready to fend for itself. 

African Cuckoos

African Cuckoos Cuculus gularis lay their eggs exclusively in the nests of Fork-tailed Drongos Dicrurus adsimilis. When the cuckoo egg hatches, the cuckoo chick ejects all the drongo eggs from the nest, so it alone gets all the food from the drongo parents.

We’ve studied the interaction between these two species in the field since 2009. Drongos build open-cup nests which are often far out along tree branches, so in order to reach the eggs we use an ‘egg spoon’ – a wire spiral spoon attached to the end of a long stick. 

African Cuckoos look extremely similar to their northern cousin, the Common Cuckoo Cuculus canorus, which has been extensively studied across Europe and Asia. Like the Common Cuckoo, they share a resemblance to Accipiter hawks, with similar plumage (including black barring on their white front), and yellow feet, beaks and ring around the eye. 

Parasitised Fork-tailed Drongo clutches. In each clutch, the African Cuckoo egg is on the right.

However, this trick seems to work less well for the African Cuckoo: drongos are highly aggressive and will attack hawks and other raptors, so looking like a hawk doesn’t help much. Drongos defend their nests by dive-bombing cuckoos, and we often find cuckoo feathers stuck to or underneath drongo nests from these interactions.

Not only do African Cuckoos face an uphill battle to get their egg into a drongo nest in the first place, but drongos are also extremely picky parents, and are very good at spotting a foreign egg in their nest. Consequently, African Cuckoo eggs have to be incredibly good drongo mimics in order to be accepted, and we’re often unsure ourselves whether an egg is a cuckoo’s or a drongo’s until it has hatched. Even though cuckoos are such good mimics, variation in egg appearance among different drongo females makes it hard for a cuckoo to get the right match in any particular nest.

Our drongos and cuckoos in Choma feature in a documentary by the BBC Natural History Unit, filmed in 2012.

Diederik Cuckoos

Diederik Cuckoos Chrysococcyx caprius are small glossy cuckoos which parasitise a large number of different host species (mostly weavers, bishopbirds, sparrows and buntings). They are related to the bronze-cuckoos of Australasia, which have been beautifully studied by Naomi Langmore and her team at Australian National University. Diederik Cuckoos are like Common Cuckoos, in that they have distinct host-specific races which mimic the eggs of each of their hosts. They have to contend with a high degree of variation in egg appearance between different females of the same host species, and have themselves evolved corresponding variation among females of the same cuckoo host-race. We haven’t studied Diederik Cuckoos in the field so far, but have tested various evolutionary questions on them with data previously obtained from our study area by Major John Colebrook-Robjent.

For example, we found that Diederik Cuckoo females parasitising thicker-shelled host species lay thicker-shelled eggs themselves. This makes sense if the function of thickened eggshells in parasites is to discourage hosts from rejecting potentially parasitic eggs, lest they damage their own eggs in the process.We’ve also studied the evolution of egg signatures in the hosts of Diederik Cuckoos, using the amazing egg collection of Major John Colebrook-Robjent which now resides in Livingstone museum, Zambia. 

For more information about Diederik Cuckoos, see the wonderful work done by David Lahti at Queens College, New York, on their interactions with their weaver hosts.