My PhD research concentrates on the coevolution occurring in brood parasite-host systems. Parasitic cuckoos and their respective host species show many adaptations and counter-adaptations which arose as evolutionary responses to the selective pressure exerted on them by one another. Evidence for these so-called evolutionary arms races has been found in many cuckoo-host systems, and it has been suggested that different species are at different stages within this race, representing “snapshots” of the evolutionary process.

My studies focus on the Jacobin cuckoo Clamator jacobinus, which parasitizes just a single species in the costal Eastern Cape region of South Africa, the Cape bulbul Pycnonotus capensis. The cuckoo lays an egg which differs from the bulbul’s in size, colouration and spottiness. Nevertheless, rejection by the bulbuls hardly occurs. Current data (Krüger, unpublished) suggests that this might be the best strategy for the bulbuls due to high rejection costs. An alternative explanation might be an evolutionary lag which has not yet given the bulbuls enough time to evolve behavioural adaptations to brood parasitism. During my PhD, I will experimentally test these hypotheses and collect data which will allow the calculation of the costs of parasitism to individual birds.

Additionally, I will address the question of how the cuckoo chick elicits sufficient food from its host parents. Jacobin cuckoos do not eject or kill their nest mates, but they often outcompete them, such that they remain the only chick in the nest. Because of their higher food requirements, they then face the problem of stimulating the host parents’ feeding more than a single bulbul chick would. I will compare both the bulbul and the cuckoo chicks’ begging behaviour and the adult bulbuls’ response to putative feeding stimuli given by the chicks.

(Left) Cape Bulbul, (Above right) Jacobin Cuckoo.