Male cuckoo calling, having just displaced another male from a favourite perch.
Wicken Fen, 21 June 2014.
Cuck-oo . . . Cuck-oo . . .
As common cuckoos arrive back in Britain from their African winter quarters, the male’s far-carrying call is a welcome harbinger of spring. For centuries, this has been a sign that the cold, dark days of winter are coming to an end, raising our spirits in anticipation of the warmth of the sun returning and a season of new growth. The oldest song in English, which dates from around AD 1250, is the cuckoo song:
Sumer is icumen in,
Lhude sing cuccu,
Groweth sed, and bloweth med,
And springeth the wode nu,
Sing cuccu!
For the oldest reference to the cuckoo in European literature, we have to go back over 2,500 years, to ancient Greece in c.700 BC, when Hesiod recommended that the best time for ploughing is as the cranes are arriving for winter (mid-November), but otherwise it’s better to wait for signs of spring, when the first cuckoos are calling (March).
The name common cuckoo is apt: the breeding range of the species extends across two-fifths of the earth’s land surface, including not only the whole of Europe (except for Iceland), but stretching east through Asia, across Siberia to Japan, and south to the Himalayas, China and southeast Asia. Cuckoos that breed in the west of this range winter south of the Sahara, in Africa, while those breeding in the east winter in southern Asia.
Every spring, then, we can imagine waves of cuckoos passing north, right across the temperate regions of the Old World. In many languages, it’s the call that gives the bird its name, so the waves are of cuckoos announcing their own arrival. Across Europe, the first calling waves reach the Mediterranean in March:
‘cuco’ in Spain and Portugal, ‘cuculo’ in Italy, ‘koúkos’ in Greece . . .
They continue, up through central Europe:
‘coucou’ in France, ‘kuckuck’ in Germany, ‘koekoek’ in the Netherlands,
‘kukulka’ in Poland, ‘kakukk’ in Hungary . . .
And they reach northern Europe from mid-April to May:
‘cuckoo’ in the UK, ‘käki’ in Finland . . .
The waves pass north through Asia, too:
‘guguk’ in Turkey, ‘gugoo’ in Azerbaijan,
‘kuku’ in Kashmir, ‘pug-pug’ in Nepal, ‘akku’ in Bhutan.
Over this vast region of forest and open country, humans may have been listening out for cuckoos to announce the spring ever since our ancestors walked out of Africa and into Eurasia many thousands of years ago.
In Britain, the call has always been greeted with special affection by the public, and until 1940 The Times newspaper published ‘first cuckoo’ letters every year. In the race to be first, this sometimes led to over-eager claims:
From Mr Lydekker, FRS.
6 February 1913. While gardening this afternoon I heard a faint note which led me to say to my under-gardener, who was working with me, ‘Was that the cuckoo?’ Almost immediately afterwards we both heard the full double note of a cuckoo, repeated either two or three times . . . There is not the slightest doubt that the song was that of a cuckoo.
Six days later, Mr Lydekker wrote again:
12 February 1913. I regret to say that, in common with many other persons, I have been completely deceived in the matter of the supposed cuckoo of February 4. The note was uttered by a bricklayer’s labourer at work in the neighbourhood of the spot whence the note appeared. I have interviewed the man, who tells me that he is able to draw cuckoos from considerable distances by the exactness of his imitation of their notes, which he produces without the aid of any instrument.
Nevertheless, not all early records are mistaken. One year another letter, also claiming a February record, provoked a sceptical reply from an eminent ornithologist. Two days later, this expert received a parcel by post containing the body of a cuckoo.
The regular seasonal rhythm of the cuckoo’s activities is celebrated, too, in a charming poem for children written by Jane Taylor (1783–1824). It was set to music a century later by Benjamin Britten and is still sung with enthusiasm in schools across the country:
Cuckoo, cuckoo . . .
What do you do?
In April, I open my bill.
In May, I sing night and day.
In June, I change my tune.
In July, far, far I fly . . .
In August, away!
I must.
However, behind all these glad tidings there is a darker side to the life of this messenger. For many species of birds the spring invasion by cuckoos is neither charming nor a cause for celebration. The poet Ted Hughes senses a forewarning in the male’s call:
That first ribald whoop, as a stolen kiss
Sets the diary trembling.
But it is the less familiar and haunting cry of the female cuckoo that proclaims the deed is done. After laying each egg, she utters a series of chuckles as if in triumph, for the common cuckoo is Nature’s most notorious cheat. It never raises its own offspring. Instead, it lays its eggs in the nests of other birds, just one egg in each host nest. Soon after the cuckoo chick hatches, it throws the host’s eggs and young out of the nest. Every summer, millions of small birds will have their eggs and chicks tossed aside by young cuckoos. Once the cuckoo chick has claimed the nest to itself, the host parents are tricked into spending their summer raising a young cuckoo instead of their own offspring.
For me, as a naturalist and scientist, the call of the cuckoo is not only a harbinger of spring. It’s an invitation to solve an enduring puzzle: how does the cuckoo get away with such outrageous behaviour?
I have been a bird watcher all my life. I was born in the village of Formby, some 15 kilometres north of Liverpool on the coast of northwest England. One of my earliest memories is of putting out food for the birds in the garden at home and the thrill of a close view of a male chaffinch from a makeshift hide of wooden chairs. I must have been about six at the time, and I had never seen anything so beautiful. I became hooked for ever. Every autumn, pink-footed geese would arrive from their Icelandic breeding grounds to winter on the farmland behind the village. Skeins flew over our house at dusk on their way to roost and, when they became disoriented on foggy nights, I lay in bed marvelling at their cries.
I have no idea where this early passion for natural history came from; my parents encouraged me, but neither they nor my siblings (two younger brothers and a younger sister) developed this obsession. By the age of nine I was keeping neat records of the species I had seen. My first notebook lists 137 bird species for the year and has an entry for 1 May: ‘Cuckoo calling, first of the summer!’ – the exclamation a mark of my excitement. Perhaps I was already imprinted on cuckoos and the wide skies of the open countryside back in those boyhood days.
During my teenage years I began to learn that there was more to natural history than simply making lists of what I’d seen. Two books in particular inspired me: The Life of the Robin by David Lack and The Herring Gull’s World by Niko Tinbergen. Lack’s study, done in the 1930s at Dartington in South Devon, involved catching robins and placing coloured rings on their legs so that individuals could be recognised and followed throughout their lives. Now I began to see the world through a bird’s eye and to appreciate the problems it faced in defending a territory, finding food and mates, choosing a place to nest, caring for its young, avoiding predators and so on. I was introduced to a scientific approach, too, namely one of asking questions about why animals behave in a particular way.
Niko Tinbergen thrilled me with his experimental approach. For example, he showed that birds reacted to simple stimuli in their environment. An adult gull would incubate any egg placed in its nest, even one of a different colour and size from its own eggs, and a begging gull chick would peck even at a cardboard model of an adult’s beak, in anticipation of a regurgitated meal. I began to dream of a life spent outside, watching and wondering about birds and the natural world.
Later, when I was a biology student at Cambridge University, I often cycled out to Wicken Fen, a patch of old fenland 15 kilometres northeast of the city. It was here that I saw my first cuckoo egg in a reed warbler nest, and then watched reed warblers hard at work feeding a cuckoo chick. Perhaps this experience finally sealed my fate, because when I returned to Cambridge in my late twenties, to teach and do research in animal behaviour and ecology, my thoughts turned to the cuckoo once more, and I began to wonder about how it tricks its hosts.
Surely, I thought, the hosts should throw out any cuckoo eggs that appeared in their nests. If hosts did that, perhaps cuckoos would then evolve an egg that was hard to detect, one that looked exactly like the host’s own eggs. What would the hosts do then? Would they be doomed to always accept the cuckoo’s egg, or could they evolve other defences? It began to dawn on me that this would be a wonderful opportunity to study cheating in nature, with the potential to discover a natural ‘arms race’ in which host defences and cuckoo trickery might evolve together, side by side.
Together with my colleagues, I have been studying this evolutionary battle between cuckoos and hosts for the past 30 years. The aim of this book is to take the reader on a journey, to discover how evolution has designed host defence and cuckoo trickery. My hope is that this reads like a nature detective story, as we uncover how the cuckoo has tricks to slip past host defences, to lay its egg and to entice the hosts to feed its chick. Just as a detective has to examine details to solve a crime, so the naturalist has to look closely too – at adult cuckoo behaviour, at cuckoo egg colour and markings, and at cuckoo chick begging calls – to work out exactly how cuckoos trick their hosts.
Sometimes we will follow the cuckoo’s trail simply by watching carefully. But cuckoos are secretive, so we will also need the tools of forensic science, such as DNA profiles and satellite tracking. We will make some shocking discoveries as we learn of the ingenious and often ruthless methods that cuckoos employ to trick and manipulate their hosts. This trickery is not confined to adult cuckoos; some of the most surprising tricks are those that cuckoo chicks use to persuade their foster parents to feed them.
However, I want not only to discover how cuckoos behave, I want to explain why they behave the way they do. This will entail asking questions about why various tricks are successful in deceiving hosts. For this part of our investigation we need to follow our watching by wondering, to form hypotheses. We will then follow Tinbergen’s lead and test our ideas, our hunches, by field experiments. For example, with the aid of model eggs painted various colours, we will investigate why hosts are tricked into accepting a cuckoo egg as one of their own. Experiments with stuffed cuckoo mounts will help us to discover why the female cuckoo has to be so quick when she visits a host nest to lay her egg. Broadcasts of chick calls at a nest will reveal why the begging calls of cuckoo nestlings are so effective at manipulating their foster parents. The results of these experiments will often produce surprises, sometimes revealing that our favourite hypotheses are wrong and sending us off down new paths of discovery.
Wicken Fen has been my outdoor laboratory for the past 30 years. It might seem obsessive to have studied cuckoos for so long in one place. But each spring I’m as excited as ever by the first cuckoo call of the year, and because a human brain can never hold all the wonderful sights and sounds of the natural world, every summer comes as a fresh surprise. I love the fen in all its moods: the ever-present sound of reeds whispering in the breeze; the succession of flowers through the season, from the pale pinks of lady’s smock that bloom when the first cuckoos arrive in April, to the yellow irises and red marsh orchids in May and June, when cuckoos lay their eggs, to the purple marsh thistles and creamy meadowsweet in July, as adult cuckoos depart for Africa once more. I have tried to convey the excitement of being a curious naturalist in the field, so the atmosphere of the fens looms large. Each year has brought new discoveries and these, in turn, raise new questions, so the science is refreshed too, and the journey is never-ending.
However, our detective work will take us way beyond the Fen, to study common cuckoos and their hosts not only throughout the UK, but across Europe to Japan. We will discover that evolutionary change is relentless. In some places, cuckoos are encountering new host species, which are only just beginning to evolve defences. We will also find isolated populations of hosts that are no longer parasitised and are slowly losing their defences. These are thrilling examples of evolution in action, a corner of Darwin’s ‘entangled bank’, where animals and plants are continuously evolving to keep up with the changes in their enemies and competitors. We also travel out to Africa and Australia, in search of other cuckoo species which have been doing battle with their hosts for far longer, and where cuckoo trickery and host defences are even more intricate. Nature is always a source of surprise and wonder.
The story is a human one, too, of our changing perceptions of the natural world – from the bewilderment of those from past centuries who struggled to understand why a Creator would produce a creature that lacked any affection for its offspring, to observers now who are fascinated by the outcomes of evolution. We will pay homage to early naturalists whose discoveries laid the foundation for cuckoo studies today. They include: Aristotle, who, over 2,300 years ago, already knew that cuckoos laid their eggs in other birds’ nests; William Turner from the sixteenth century, who wrote the first book about birds in Britain; John Ray from the seventeenth century and Gilbert White from the eighteenth century, both puzzled by the cuckoo’s parasitic habits; White’s contemporary Edward Jenner, whose first detailed descriptions of a cuckoo chick evicting host eggs and chicks from the nest were so astonishing that they were widely disbelieved; Charles Darwin, Alfred Russel Wallace and Henry Walter Bates, evolutionary thinkers and brilliant field naturalists from the nineteenth century; Alfred Newton, from the late nineteenth century, who wrote about the various races of common cuckoos, each specialising on a particular host species; Edgar Chance, a passionate egg collector from the early twentieth century, who was the first to discover how the cuckoo lays her egg; and Charles Swynnerton, another naturalist from the early twentieth century, who pioneered studies of cuckoos and their eggs in Africa.
These are all heroes, but I feel a special bond with two of them. In 1530, William Turner was elected a Fellow of Pembroke College in Cambridge, the college where I was a student and where I’ve been a Fellow, too, since 1979. His book on birds, published in 1544, has a ‘Peroration to the reader’ that heralds a change in our view of the natural world, from the unquestioning acceptance of folklore to fresh scientific enquiry:
This little book of mine contains within it many more conjectures than sure statements . . . it seemed to me much more prudent and becoming on a subject that is difficult and not yet sufficiently explored to tread doubtingly and modestly by conjecture, and so to enquire, than to pronounce rashly and immodestly on things undetermined.
My concerns about cuckoos are very different from those of Turner, nearly 500 years ago, but I hope his spirit of asking questions of nature and admitting when we don’t know all the answers lives on in my book, too.
The other person peering over my shoulder as I wrote is Alfred Newton, Professor of Comparative Anatomy at the University of Cambridge. When he died in 1907, he bequeathed his grand old desk to the Zoology Department, where I have studied and taught for most of my life. I am privileged to have this in my room, and so have written my book at the very same desk on which Newton wrote about cuckoos, over 100 years ago.
Today, there are no more ‘first cuckoo’ letters to The Times. If there were, they would probably be letters remarking on the silence, wondering where all the cuckoos have gone to, for there has been an alarming decline in the last 50 years or so. I hope, by the end of our journey, that the reader will agree with me that their disappearance would be doubly sad: we would lose not only our harbinger of spring, but also some of the most amazing dramas of natural history anywhere on earth.