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The cuckoo, common cuckoo, European cuckoo or Eurasian cuckoo ( Cuculus canorus) is a member of the cuckoo order of birds, Cuculiformes, which includes the Geococcyx, the anis and the .
This species is a widespread summer bird migration to Europe and Asia, and winters in Africa. It is a brood parasite, which means it lays eggs in the nests of other bird species, particularly of , , and reed warblers. Although its eggs are larger than those of its hosts, the eggs in each type of host nest resemble the host's eggs. The adult too is a mimicry, in its case of the sparrowhawk; since that species is a predator, the mimicry gives the female time to lay her eggs without being attacked.
There are four subspecies worldwide:
All adult males are slate-grey; the grey throat extends well down the bird's breast with a sharp demarcation to the barred underparts. The iris, orbital ring, the base of the bill and feet are yellow. Grey adult females have a pinkish-buff or buff background to the barring and neck sides, and sometimes small rufous spots on the median and greater coverts and the outer webs of the secondary feathers.
Rufous morph adult females have reddish-brown upperparts with dark grey or black bars. The black upperpart bars are narrower than the rufous bars, as opposed to rufous juvenile birds, where the black bars are broader.
Common cuckoos in their first autumn have variable plumage. Some have strongly-barred chestnut-brown upperparts, while others are plain grey. Rufous-brown birds have heavily barred upperparts with some feathers edged with creamy-white. All have whitish edges to the upper wing-coverts and primaries. The secondaries and greater coverts have chestnut bars or spots. In spring, birds hatched in the previous year may retain some barred secondaries and wing-coverts. The most obvious identification features of juvenile common cuckoos are the white nape patch and white feather fringes.
Common cuckoos moult twice a year: a partial moult in summer and a complete moult in winter. Males weigh around and females . The common cuckoo looks very similar to the Oriental cuckoo, which is slightly shorter-winged on average. This resemblance extends even to the rufous morphs, which are also present in Oriental cuckoos. The presence of rufous morphs may well be ancestral to both Oriental cuckoos and common cuckoos.
Hosts attack cuckoos more when they see neighbors mobbing cuckoos. The existence of the two plumage morphs in females may be due to frequency-dependent selection if this learning applies only to the morph that hosts see neighbors mob. In an experiment with dummy cuckoos of each morph and a sparrowhawk, reed warblers were more likely to attack both cuckoo morphs than the sparrowhawk, and even more likely to mob a certain cuckoo morph when they saw neighbors mobbing that morph, decreasing the reproductive success of that morph and selecting for the less common morph.
Female common cuckoos are divided into gentes – groups of females favouring a particular host species' nest and laying eggs that match those of that species in color and pattern. Evidence from mitochondrial DNA analyses suggest that each gente may have multiple independent origins due to parasitism of specific hosts by different ancestors. One hypothesis for the inheritance of egg appearance mimicry is that this trait is inherited from the female only, suggesting that it is carried on the sex-determining W chromosome (females are WZ, males ZZ). A genetic analysis of gentes supports this proposal by finding significant differentiation in mitochondrial DNA, but not in microsatellite DNA. A second proposal for the inheritance of this trait is that the genes controlling egg characteristics are carried on rather than just the W chromosome. Another genetic analysis of Sympatry gentes supports this second proposal by finding significant genetic differentiation in both microsatellite DNA and mitochondrial DNA. Considering the tendency for common cuckoo males to mate with multiple females and produce offspring raised by more than one host species, it appears as though males do not contribute to the maintenance of common cuckoo gentes. However, it was found that only nine percent of offspring were raised outside of their father's presumed host species. Therefore, both males and females may contribute to the maintenance of common cuckoo egg mimicry polymorphism. It is notable that most non-parasitic cuckoo species lay white eggs, like most non-passerines other than ground-nesters.
As the common cuckoo evolves to lay eggs that better imitate the host's eggs, the host species adapts and is more able to distinguish the cuckoo egg. A study of 248 common cuckoo and host eggs demonstrated that female cuckoos that parasitised common redstart nests laid eggs that matched better than those that targeted dunnocks. Spectroscopy was used to model how the host species saw the cuckoo eggs. Cuckoos that target dunnock nests lay white, brown-speckled eggs, in contrast to the dunnock's own blue eggs. The theory suggests that common redstarts have been parasitised by common cuckoos for longer, and so have evolved to be better than the dunnocks at noticing the cuckoo eggs. The cuckoo, over time, has needed to evolve more accurate mimicking eggs to successfully parasitise the redstart. In contrast, cuckoos do not seem to have experienced evolutionary pressure to develop eggs which closely mimic the dunnock's, as dunnocks do not seem to be able to distinguish between the two species' eggs, despite the significant colour differences. The dunnock's inability to distinguish the eggs suggests that they have not been parasitised for very long, and have not yet evolved defences against it, unlike the redstart.
Studies performed on great reed warbler nests in central Hungary, showed an "unusually high" frequency of common cuckoo parasitism, with 64% of the nests parasitised. Of the nests targeted by cuckoos, 64% contained one cuckoo egg, 23% had two, 10% had three and 3% had four common cuckoo eggs. In total, 58% of the common cuckoo eggs were laid in nests that were multiply parasitised. When laying eggs in nests already parasitised, the female cuckoos removed one egg at random, showing no discrimination between the great reed warbler eggs and those of other cuckoos.
It was found that nests close to cuckoo perches were most vulnerable: multiple parasitised nests were closest to the vantage points, and unparasitised nests were farthest away. Nearly all the nests "in close vicinity" to the vantage points were parasitised. More visible nests were more likely to be selected by the common cuckoos. Female cuckoos use their vantage points to watch for potential hosts and find it easier to locate the more visible nests while they are egg-laying, however, novel studies highlight that host alarm calls might also play an important role during nest searching. In addition, cuckoos tend to lay the eggs on the host clutch initiation day or one day before.
The great reed warblers' responses to the common cuckoo eggs varied: 66% accepted the egg(s); 12% ejected them; 20% abandoned the nests entirely; 2% buried the eggs. 28% of the cuckoo eggs were described as "almost perfect" in their mimesis of the host eggs, and the warblers rejected "poorly mimetic" cuckoo eggs more often. The degree of mimicry made it difficult for both the great reed warblers and the observers to tell the eggs apart.
The egg measures and weighs , of which 7% is shell. Research has shown that the female common cuckoo is able to keep its egg inside its body for an extra 24 hours before laying it in a host's nest. This means the cuckoo chick can hatch before the host's chicks do, and it can eject the unhatched eggs from the nest. Scientists incubated common cuckoo eggs for 24 hours at the bird's body temperature of , and examined the embryos, which were found "much more advanced" than those of other species studied. The idea of 'internal incubation' was first put forward in 1802 and 18th- and 19th-century egg collectors had reported finding that cuckoo embryos were more advanced than those of the host species.
A study using digital photography and spectroscopy along with an automatic analytical approach to analyse cuckoo eggs and predict the identity of bird females based on their egg appearance showed that individual cuckoo females lay eggs with a relatively constant appearance, and that eggs laid by more genetically distant females differ more in colour.
Complete list of common cuckoo's nest-host by Aleksander D. Numerov (2003); names of birds in whose nests cuckoo's eggs and chicks were found more than 10 times (in bold):Numerov, A. D. Inter-species and Intra-species brood parasitism in Birds. Voronezh: Voronezh University. 2003. 516 p. In Нумеров А. Д. Межвидовой и внутривидовой гнездовой паразитизм у птиц. Воронеж: ФГУП ИПФ Воронеж. 2003. C. 38-40.
The necessity of eviction behavior is unclear. One hypothesis is that competing with host chicks leads to decreased cuckoo chick weight, which is selective pressure for eviction behavior. An analysis of the amount of food provided to common cuckoo chicks by host parents in the presence and absence of host siblings showed that when competing against host siblings, cuckoo chicks did not receive enough food, showing an inability to compete. Selection pressure for eviction behavior may come from cuckoo chicks lacking the correct visual begging signals, hosts distributing food to all nestlings equally, or host recognition of the parasite. Another hypothesis is that decreased cuckoo chick weight is not selective pressure for eviction behavior. An analysis of resources provided to cuckoo chicks in the presence and absence of host siblings also showed that the weights of cuckoos raised with host chicks were much smaller upon fledging than cuckoos raised alone, but within 12 days cuckoos raised with siblings grew faster than cuckoos raised alone and made up for developmental differences, showing a flexibility that would not necessarily select for eviction behavior.
Species whose broods are parasitised by the common cuckoo have evolved to discriminate against cuckoo eggs but not chicks. Experiments have shown that common cuckoo chicks persuade their host parents to feed them by making a rapid begging call that sounds "remarkably like a whole brood of host chicks". The researchers suggested that "the cuckoo needs vocal trickery to stimulate adequate care to compensate for the fact that it presents a visual stimulus of just one gape". However, a cuckoo chick needs the amount of food of a whole brood of host nestlings, and it struggles to elicit that much from the host parents with only the vocal stimulus. This may reflect a tradeoff—the cuckoo chick benefits from eviction by receiving all the food provided, but faces a cost in being the only one influencing feeding rate. For this reason, cuckoo chicks exploit host parental care by remaining with the host parent longer than host chicks do, both before and after fledging.
Common cuckoo chicks fledge about 17–21 days after hatching, compared to 12–13 days for Eurasian reed warblers. If the hen cuckoo is out-of-phase with a clutch of Eurasian reed warbler eggs, she will eat them all so that the hosts are forced to start another brood.
The common cuckoo's behaviour was firstly observed and described by Aristotle and the combination of behaviour and anatomical adaptation by Edward Jenner, who was elected as Fellow of the Royal Society in 1788 for this work rather than for his development of the smallpox vaccine. It was first documented on film in 1922 by Edgar Chance and Oliver G. Pike, in their film The Cuckoo's Secret. A study in Japan found that young common cuckoos probably acquire species-specific Bird louse from body-to-body contact with other cuckoos between the time of leaving the nest and returning to the breeding area in spring. A total of 21 nestlings were examined shortly before they left their hosts' nests and none carried feather lice. However, young birds returning to Japan for the first time were found just as likely as older individuals to be lousy.
The 13th-century Middle English round "Sumer is icumen in" celebrates the cuckoo as a sign of spring, the beginning of summer, in the first stanza, and in the chorus:
In England, William Shakespeare alludes to the common cuckoo's association with spring, and with cuckoldry, in the courtly springtime song in his play Love's Labours Lost:
In Europe, hearing the call of the common cuckoo is regarded as the first harbinger of spring. Many local legends and traditions are based on this. In Scotland, (cuckoo stones) sometimes associated with the arrival of the first cuckoo of spring. is an old name for the common cuckoo in northern England. The well-known cuckoo clock features a mechanical bird and is fitted with bellows and pipes that imitate the call of the common cuckoo. Cuckoos feature in traditional rhymes, such as '"In April the cuckoo comes, In May she'll stay, In June she changes her tune, In July she prepares to fly, Come August, go she must,"' quoted Peggy. 'But you haven't said it all,' put in Bobby. '"And if the cuckoo stays till September, It's as much as the oldest man can remember."'
On Hearing the First Cuckoo in Spring is a symphonic poem from Norway composed for orchestra by Frederick Delius. "On Hearing the First Cuckoo in Spring". IMSLP Petrucci Library. Retrieved 4 October 2019.
Two English folk songs feature cuckoos. One usually called The Cuckoo starts:
The cuckoo is a fine bird and she sings as she flies,
She brings us good tidings, she tells us no lies.
She sucks little birds' eggs to make her voice clear,
And never sings cuckoo till the summer draws nearPalmer, Roy (ed); English Country Songbook; London; 1979
The second, "The Cuckoo's Nest" is a song about a courtship, with the eponymous (and of course, non-existent) nest serving as a metaphor for the vulva and its tangled "nest" of pubic hair.
Some like a girl who is pretty in the face
and some like a girl who is slender in the waist
But give me a girl who will wriggle and will twist
At the bottom of the belly lies the cuckoo's nest...
...Me darling, says she, I can do no such thing
For me mother often told me it was committing sin
Me maidenhead to lose and me sex to be abused
So have no more to do with me cuckoo's nest
One of the tales of the Wise Men of Gotham tells how they built a hedge round a tree in order to trap a cuckoo so that it would always be summer.
The theme music for film comedians Laurel and Hardy, titled "Dance of The Cuckoos" and composed by Marvin Hatley, was based on the call of the common cuckoo.
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