The Secret Crimes of the Cuckoo

springwatch the con is on The CON isON Cavan Scott investigates the crimes of the star of this year’s Springwatch David Kjaer /naturepl.com Photo: may 2009 COUNTRYFILE 49 springwatch the con is on such extraordinary lengths, and worldwide only around 1 percent “Within hours of hatching of all birds share its methods. the blind and naked cuckoo After 23 years studying the cuckoo’s sinister plans in Wicken chick pushes any remaining Fen, Britain’s foremost expert on cuckoo behaviour, Dr Nicholas eggs from the nest” Davies of the University of Cambridge, is able to shed some light on the matter. 1 “Foisting your parental duties on somebody else may seem to be a wonderful thing to do,” he explains. “But over evolutionary time, the hosts fight back so that the poor cuckoo has to work 2 3 incredibly hard to be lazy, simply because it has to overcome all of these defences. What we witness is a fantastic arms race between parasite and host.” 4 5 This titanic battle commences with that famous bird call. In May, A host of hosts the blue-grey male cuckoo arrives In Britain, five main hosts account for on our shores from Africa and 90 percent of the parasitised nests. booms out his distinctive ‘cuc-coo’, In heathland the cuckoo will choose thereby establishing himself as the dunnock (1), in marshland it picks God’s gift to the slightly browner the reed warbler (2), while in open female. Nature takes its course and country it’s the pied wagtail (3). The meadow pipit (4) falls foul of the the female’s work begins. cuckoo’s machinations in moorland, while the nation’s favourite bird, the Watching and waiting robin (5), is the cuckoo’s choice for If you think you’re a good farm and woodland. Of all the cuckoo’s victims, the dunnock puts up the least birdwatcher, you’ve nothing on resistance, leaving experts to theorise the female cuckoo. Perching that it’s a more recent target for the motionless in a tree she will lay cuckoo’s crime, and hasn’t had do in wait, monitoring the nests of much time to evolve its defences. her potential victims. When the host is away feeding, the cuckoo They are nature’s place? Why doesn’t the cuckoo soon as possible. Around the same strikes, silently swooping into the hustlers, cheats that just rear its own young, instead time, the famed naturalist Gilbert empty nest and gobbling down have perfected the of abdicating responsibility to its White guessed that the cuckoo’s one of the host’s eggs so that her David Tipling, ultimate long con. poor victims? substantial stomach meant that own, which she speedily lays, is But even though they As we strain to hear the first it couldn’t incubate its eggs. To offered better incubation. Her job reed warbler) reed ( are born with an instinctive need call of the harbinger of spring, it’s White, the desertion of the eggs done she zooms off, never to see to murder, our spirits are raised time to turn nature detective and was a “monstrous outrage on her offspring again. The entire when we hear their cry. In fact, discover the true story behind the maternal affection”. operation takes just 10 seconds. Terry Button, Stephen Dalton/NHPA their song is one of the few bird cuckoo’s fascinating crime. But it was Charles Darwin who But why does she have to be calls that just about anyone can cut to the chase in 1859’s On the so quick? Davies’s experiments (Dunnock) (meadow pipit) identify, whether you’re a birder Speculative theories Origin of Species. He identified the hold the answer. With his team, or not. It’s a crime that has captivated immense benefit of being a brood he planted stuffed cuckoos near Andy Hay, The story of the cuckoo’s nature lovers for centuries. In parasite. Freed from parental reed warblers’ nests. When the treachery is well known, but have the 18th century, Edward Jenner duties, the cuckoo was able to lay warblers spotted this threat they (pied wagetail) you ever stopped to think how first recorded a newly hatched many more eggs than its victims. attacked the fake bird, and after it they do it? Why does the tiny reed cuckoo’s murderous rampage. However, Darwin’s observation was removed they were more likely warbler or meadow pipit spend Puzzled by the migratory cuckoo’s prompts one question: if the to check their clutch, rejecting Mike Richards rspb-images.com); (all Martin Hamblin, its spring tearing around to feed parasitical existence, he suggested cuckoo’s con is so effective, why eggs that they didn’t believe were the gargantuan interloper that is that the adult birds simply didn’t aren’t more birds at it? Of all of theirs. It’s the same as when you (Cuckoo) (Cuckoo) spilling out of its nest? And why have time to raise their young, British birds, only the common suddenly decide to install a burglar Photos: (newly hatched chick) bother with the deceit in the first needing to nip back to Africa as cuckoo (Cuculus canorus) goes to alarm after you’ve heard about 50 COUNTRYFILE MAY 2009 MAY 2009 COUNTRYFILE 51 springwatch the con is on robberies in the area. If the hosts are alerted to the presence of a cuckoo they are more suspicious of the eggs in their nest. But if they are unaware, they will incubate the interloper in blissful ignorance. Recent research has also shown that if the cuckoo is discovered and mobbed by its victims, the resulting hullabaloo is more likely to bring the nest to the attention of predators, thereby putting the cuckoo’s precious egg in jeopardy. To ensure that they can trick the hosts, the cuckoo has evolved to produce eggs that perfectly mimic the host’s own. They specialise in one species and pass the ability down to their young. The cuckoo chick is a master impressionist, Evolution in action leading the reed warbler to believe it’s Over a period of two years, Davies feeding its own hungry chicks added painted wooden eggs of various sizes and colours to reed But even if the host had been warblers doubled their efforts to warblers’ nests. If they were even hoodwinked into incubating a feed the chick. The alarming slightly different to the bird’s perfectly matched egg, surely As the chick gets older the decline of own clutch they were pushed out they notice that their baby is intensity of its begging cry of the nest. The experiment also twice their size? Early in his increases to make the hosts work the cuckoo highlighted another aspect of this research, Nicholas wondered if harder, victims of what Darwin Clever though the cuckoo may be, the battle. “Hosts that are targeted by the chick’s immense proportions called “mistaken instinct”. The bird is in long-term decline in the UK. cuckoos evolve less variation were the reason that the hosts host is hard-wired to feed its The last 30 years have seen the cuckoo in their own eggs,” he explains. were confused into feeding the hungry young, and so the con population slump by 47 percent and “This makes very good sense. chick, which eats about the same works. After 19 days the cuckoo is the bird is expected to join the ICUN It’s easier to spot a strange egg if amount as four ravenous reed literally bursting from its nest and Red List of threatened species this year. The decline is a mystery. The all of your eggs look the same. So warblers. Yet when he replaced a will still be supported by its poor cuckoo can live in every habitat, so the cuckoo had to develop an even cuckoo chick with a similarly sized foster parents for a further two it shouldn’t be susceptible to local better match.” blackbird, the reed warblers cut weeks, before abandoning them to problems, but there are a few main While this mimicry is fantastic, back on feeding. Then he twigged head to Africa. theories as to why numbers are falling: the real jaw-dropping moment that while the mother cuckoo uses So, we know how the cuckoo The cuckoo feeds on hairy moth comes when the chick is born. visual trickery, the baby uses aural. pulls off its dastardly plan, but still caterpillars, which themselves are The cuckoo’s egg has a head “The cuckoo chick has this haven’t answered the question of in decline. start, requiring half-a-day’s less amazing begging call,” he says. why. Is it a cruel or evil bird? Of If the hosts, such as meadow pipits, incubation than the host’s clutch, “It sounds like a whole brood of course not. This is just nature at are in decline then it seems logical possibly due to the fact that newly hungry chicks. So we repeated work, and perhaps one of the best that the cuckoos would also suffer. Certainly, it’s easier to spot cuckoos laid cuckoo eggs contain partly the blackbird experiment, giving examples of Darwin’s survival in marshlands, where reed warblers developed embryos. The chick’s it a helping hand in the form of of the fittest. The arms race will are doing very well. homicidal tendencies are just a little loudspeaker next to nest. continue, with both sides evolving There has been a mysterious as developed, and within hours Every time the blackbird begged, to protect themselves or deceive decrease in migratory birds.

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