African and Diederik Cuckoos

Introduction

African Cuckoo ejecting

An African Cuckoo hatchling ejects the egg of a Fork-tailed Drongo.

Diederik Cuckoos Chrysococcyx caprius are small glossy cuckoos related to the bronze-cuckoos of Australasia, which have been beautifully studied by Naomi Langmore and her team at Australian National University. Diederik Cuckoos parasitise a large number of different host species (mostly weavers, bishopbirds, sparrows and buntings) and, like Common Cuckoos, they have distinct host-specific races which mimic the eggs of each of their hosts. Like African Cuckoos and Cuckoo Finches, they have to contend with a high degree of variation in egg appearance between different females of the same host species, and in turn 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 (see publication below). 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. 

Collins lowering cuckoo

An African Cuckoo chick being lowered from a drongo nest in a Mubula (Parinari curatellifolia) tree by Collins Moya.

We have studied African Cuckoos Cuculus gularis and their interactions with their host, the Fork-tailed Drongo Dicrurus adsimilis, in the field since 2009. African Cuckoos look extremely similar (and are closely related) to the Common Cuckoo Cuculus canorus of the northern hemisphere, which has been beautifully studied for many years by scientists in Europe and Asia. Like Common Cuckoos and indeed all other cuckoo species in the subfamily Cuculinae, African Cuckoo chicks eject any host eggs or chicks from the nest a few days after hatching. 

Unlike Common Cuckoos, though, African Cuckoos parasitise just one host species, so they have not evolved host-specific races that mimic the eggs of different host species: they only need to mimic drongos.

However, this is not so straightforward: drongos are formidably well-defended hosts. In addition to defending their nests highly aggressively (we often find cuckoo feathers stuck to or underneath drongo nests), Fork-tailed Drongos are extremely picky parents. Not only do they show variation in egg appearance among different females which makes it hard for a cuckoo to produce a perfect mimic (just like Cuckoo Finch hosts), but they are also extremely 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.

In 2012, the BBC Natural History Unit came to Choma to film our drongos and cuckoos for a forthcoming TV series. 

We also found that host species of the Diederik Cuckoo defend themselves against cuckoo parasitism by evolving unpredictable visual signatures on their eggs (left): host species of many brood-parasitic birds have evolved features such as spots, squiggles and colours on their eggs that act like ‘signatures’ that are difficult for parasites to forge, helping hosts to detect and reject imposter eggs. In this paper, we show that hosts of Diedierik Cuckoos (as well as of Cuckoo Finches) in Zambia have optimised this defence by arranging signature traits in unpredictable combinations. Thus, egg signatures are individually distinctive and hard for parasites to mimic, helping hosts distinguish parasitic eggs from their own. The paper arose from MPhil research by Eleanor Caves and the data were all obtained from Major John Colebrook-Robjent’s wonderful egg collection. (Read the full paper on the journal website [Open Access])

For more information about Diederik Cuckoos please also see the website of David Lahti at Queens College, New York, who has done wonderful work on their interactions with their weaver hosts.

Cuckoo research in the news

Article about internal incubation by cuckoos and honeyguides: BBC News website.

Our Cuckoo publications

  • Caves, E.M., Stevens, M. & Spottiswoode, C.N. 2017 Does coevolution with a shared parasite drive hosts to partition their defences among species? Proceedings of the Royal Society of London B 284: 20170272 Read on journal website [Open Access]

  • Caves, E.M., Stevens, M., Iversen, E. & Spottiswoode, C.N. 2015 Hosts of brood parasites have evolved egg signatures with elevated information content. Proceedings of the Royal Society of London B 282: 20150598. Read on journal website [Open Access]

  • Birkhead, T.R., Hemmings, N., Spottiswoode, C.N., Mikulica, O, Moskát, C., Bán, M. & Schulze-Hagen, K. 2011 Internal incubation and early hatching in brood parasitic birds. Proceedings of the Royal Society of London B 278, 1019-1024 Read on journal website [Open Access]

  • Spottiswoode, C.N. 2010 The evolution of host-specific variation in cuckoo eggshell strength. Journal of Evolutionary Biology 23: 1792-1799. Read on journal website [Open Access]

News

Evolutionary Biology Crash Course

Tanmay Dixit was a member of a team organising and lecturing in the inaugural Evolutionary Biology Crash Course. This course, aimed at undergraduate or early-postgraduate students, teaches evolutionary principles to students who have had limited opportunities to be exposed to evolutionary ideas. The course is funded by the Equal Opportunities Initiative Fund of the European Society of Evolutionary Biology (ESEB). Tanmay presented lectures on behavioural ecology and evolution, focussing on kin selection, coevolution, and parasitism. Over 700 students, with the vast majority from the global South, attended the course, which was a resounding success!

read more

New paper on visual complexity & mimicry

Our paper “Visual complexity of egg patterns predicts egg rejection according to Weber’s Law” has just been published in the journal Proceedings of the Royal Society B. This research was led by Tanmay Dixit, and carried out together with Andrei Apostol, Kuan-Chi Chen, Tony Fulford, Chris Town and Claire Spottiswoode, in a collaboration between biologists and computer scientists. We used machine learning to compute a biologically-relevant measure of egg pattern complexity, and combined this with field experiments in Zambia to investigate how complexity evolves in an arms race between host egg signatures (by tawny-flanked prinias) and parasitic egg forgeries (by cuckoo finches).

read more

Fieldwork and teaching at APLORI, Nigeria

Dr Gabriel Jamie is continuing his fieldwork on the evolution of polymorphisms in cisticolas and prinias in Nigeria, where he is also a teaching fellow at the AP Leventis Ornithological Research Institute (APLORI). The image shows the 2022 APLORI MSc class during the Global Birding Big Day on 14 May. The team recorded 135 species while walking around the nature reserve surrounding the institute.

read more

New paper on the genetics of cuckoo finch egg mimicry

Our paper “Genetic architecture facilitates then constrains adaptation in a host-parasite coevolutionary arms race” has been published in the Proceedings of the National Academy of Sciences of the USA. In it, we address the long-standing puzzle of how exquisite mimicry of the eggs of several different host species can evolve within a single species of brood-parasitic bird. We show that in cuckoo finches in Zambia, egg mimicry of different host egg phenotypes is maternally inherited, which allows mothers to transmit host-specific adaptations to their daughters irrespective of which host species the father was raised by. This study was a team effort from colleagues at the University of Cambridge and University of Cape Town (Claire Spottiswoode, Wenfei Tong, Gabriel Jamie), at Boston University (Katherine Stryjewski, Jeff DaCosta, Evan Kuras and Michael Sorenson) and in the Choma community in Zambia (Ailsa Green, Silky Hamama, Ian Taylor and Collins Moya).

read more