Cuckoo: cheating by nature

Published on 11 June 2015 in Book reviews

CuckooBy Nick Davies

Bloomsbury, 2015; hbk, 289pp; 21 colour and five black-and-white photographs, several illustrations

ISBN 978-1-4088-5656-7, £16.99

Everyone knows the Common Cuckoo Cuculus canorus, by voice if not by sight. For generations, it has been welcomed as a harbinger of spring, and is known as the only bird in Britain that is a brood parasite. The unwitting foster parents then raise the young Cuckoo after it has thrown their own eggs and chicks out of the nest. It is this amazing story of cheating, trickery and gullibility that Nick Davies has studied for 30 years and which he tells so engagingly in this book. Nick is Professor of Behavioural Ecology at the University of Cambridge, and most of his studies were made at nearby Wicken Fen, where Cuckoos lay in the nests of Reed Warblers Acrocephalus scirpaceus.

Some aspects of Cuckoo behaviour had been uncovered between 1918 and 1922 by the remarkable Edgar Chance, a businessman glass-maker who studied Cuckoos parasitising Meadow Pipits Anthus pratensis on heathland in the Wyre Forest, in Worcestershire. By then it was accepted that Cuckoos must exist in the form of several races (gens), each specialising on a different main host – Reed Warbler, Meadow Pipit, Dunnock Prunella modularis and Pied Wagtail Motacilla alba being the main host species in Britain. Before the advent of DNA, the most obvious difference between these Cuckoo races was in their differently coloured eggs, which were generally similar in appearance to their host eggs (or at least were of a colour that was accepted by the host).

Davies and his colleagues have added much that is new to these early studies. By use of observation and elegant field experiments, they set out to answer some fundamental questions about the interactions between Cuckoos and their hosts. What does the Cuckoo do to trick its hosts into accepting a strange egg in their nest and to feed such an oversized chick which looks nothing like their own young? Why do the hosts accept the egg and young of a Cuckoo in their nest, rather than discarding the egg or deserting the chick? Why does the level of egg mimicry vary, with some Cuckoo races laying eggs that look almost identical to the host eggs, and others (such as Dunnock Cuckoos) laying eggs that look strikingly different from the host eggs?

The research has uncovered one of the best examples yet described of an ‘evolutionary arms race’, in which hosts evolve ever better defences against Cuckoos, and Cuckoos in turn come up with more novel forms of trickery. Different stages in this arms race can be seen in different races of Common Cuckoos in Britain and across their range, as they exploit different host species. But even further advances in the arms race can be seen in other parasitic birds around the world, with some amazing examples from honeyguides (Indicatoridae) and Vidua finches in Africa, and bronze cuckoos Chrysococcyx in Australia. Their individual stories provide great insight into the way that cheating and forgery evolve and thrive in the natural world.

One frequently asked question is why Cuckoos parasitise such a narrow range of host species, when many other common species of similar size have nests and diets that would suit a young Cuckoo? Experiments on some of these potential hosts have revealed that they have effective defences, for example by ejecting or deserting strange eggs, or refusing to feed strange chicks. So could some potential Cuckoo host species in Britain and elsewhere be no longer parasitised because they have ‘won’ the arms race, and evolved effective defences? Will they eventually lose these defences, and again become vulnerable to Cuckoos, starting another arms race? One nice thing about this book is that it continually raises new questions such as these, perhaps pointing the way to another 30 years of fascinating research.

Another welcome feature of the book is that it is engagingly written in plain English, more or less as a detective story, building up the evidence from one series of experiments after another, as each set of answers raises other questions. The colour photographs of Cuckoo behaviour are dramatic and well chosen and the book is illustrated throughout by some evocative field drawings by James McCallum. I suspect that everyone with an interest in the natural world will enjoy reading this book. It illustrates dedicated field observation, detective work and experiment at its best.

Ian Newton