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What the sources say

Common CuckooCuculus canorus

Every figure, record and mechanism on the Common Cuckoo profile was written from a source, and this is the working table behind it: 54 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

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Source
01

Animal Diversity Web, University of Michigan Museum of Zoology

Cuculus canorus (common cuckoo). Animal Diversity Web, University of Michigan Museum of Zoology.

The page saysOpen country such as fields and marshes, also forest and farmland; breeds across much of Europe and migrates to central and southern Africa
The source saysCommon cuckoos live in open areas such as fields and marshes. They can also live in alpine areas, forests, or on farmland.Note: stats.habitat
The page saysbreeds across much of Europe and migrates to central and southern Africa
The source saysspends its breeding season throughout much of Europe and as far north as Sweden and RussiaNote: stats.habitat
The page saysmigrates to central and southern Africa
The source saysthe cuckoo migrates to central and southern AfricaNote: stats.habitat
The page saysInsects, including hairy caterpillars, plus the eggs and nestlings of host species
The source saysCommon cuckoos eat different types of insects, including hairy caterpillarsNote: stats.diet
The page saysplus the eggs and nestlings of host species
The source saysFemale cuckoos also eat the eggs and the nestlings of the host species.Note: stats.diet
The page saysa female takes one egg out of the host nest and lays her own in its place
The source saysThe cuckoos remove an egg from the host nest and lay their own egg.
The page saysOnce the cuckoo hatches, it removes the host's eggs and nestlings.
The source saysthe young cuckoo chicks remove the host species’ eggs and nestlings from the nest
The page saysA female visits up to fifty nests in a season and lays 12 to 22 eggs.
The source saysRange eggs per season 12 to 22
The page saysthe body length as 32 to 34 cm
The source saysRange length 32 cm to 34 cm
The page saysAdults eat insects, including hairy caterpillars that many other birds avoid
The source sayshairy caterpillars which are not eaten by many other birds
The page saysfemales also eat the eggs and nestlings of host species
The source saysFemale cuckoos also eat the eggs and the nestlings of the host species.
The page saysbreeds across much of Europe, north to Sweden and Russia
The source saysspends its breeding season throughout much of Europe and as far north as Sweden and Russia
The page saysbuilds no nest of its own
The source saysAs brood parasites, common cuckoos do not build their own nests.Note: FAQ
The page saysrelies on host parents to incubate its eggs and feed the chicks
The source saysCommon cuckoos rely on the host parents to incubate their eggs and feed the chicks.Note: FAQ
The page saysleave the nest after 17 to 21 days
The source saysCommon cuckoo chicks leave the nest after seventeen to twenty- one days.Note: FAQ; ADW gives the numbers in words
The page saysA female visits up to fifty nests in a season
The source saysthe females visit up to fifty nests and only lay between twelve to twenty-two eggs each
The page saysA Bird With No Nest
The source saysAs brood parasites, common cuckoos do not build their own nests.Note: heading
The page sayshas been found breeding as far afield as China, India and Japan
The source saysThe cuckoo has also been found breeding in areas as far south as China and India, as far east as Spain and as west as Japan
The page saysAfterwards it migrates to central and southern Africa, Vietnam, Thailand and Sri Lanka.
The source saysWhen the breeding season ends, the cuckoo migrates to central and southern Africa, Vietnam, Thailand, and Sri Lanka.

Source
02

British Trust for Ornithology

BirdFacts: Cuckoo (Cuculus canorus). British Trust for Ornithology.

The page saysBritish Trust for Ornithology figures for live adults give an average of 114.3 g, with the middle 90% between 93 and 143 g.
The source saysAll adults 114.3±15.7 g (93-143 gNote: BTO table heading: 5th and 95th percentiles, weights from live birds; 90% is the span between them
The page saysmales arrive in late April and can leave again as early as the first week of June
The source saysthe males arriving in late April and leaving again as early as the first week of June
The page saysTracked British cuckoos all winter in the same part of central Africa
The source saysall of the birds winter in the same part of central Africa
The page saysa 33% drop in the breeding population from 1995 to 2024
The source says33% decrease 1995 to 2024
The page saysestimated it at 18 thousand pairs in 2016
The source says18 thousand pairs (2016)
The page saysLive adults in the British Trust for Ornithology's figures average 114.3 g; the lightest 5% weigh under 93 g and the heaviest 5% over 143 g.
The source saysAll adults 114.3±15.7 g (93-143 gNote: FAQ; BTO table heading: 5th and 95th percentiles

Source
03

Human Ageing Genomic Resources, AnAge database

AnAge: Cuculus canorus (common cuckoo). Human Ageing Genomic Resources, AnAge database.

The page saysa maximum longevity of 12.9 years in the wild
The source saysMaximum longevity 12.9 years (wild)
The page saysThe AnAge database gives a maximum recorded longevity of 12.9 years in the wild.
The source saysMaximum longevity 12.9 years (wild)Note: FAQ

Source
04

The IUCN Red List of Threatened Species 2024

Cuculus canorus. The IUCN Red List of Threatened Species 2024: e.T22683873A264553575.

The page saysLeast Concern
The source saysIUCN Red List category: Least Concern (LC).Note: stats.conservationStatus; assessed 2024, category read through GBIF's copy of the Red List
The page saysglobally Least Concern on the IUCN Red List, assessed in 2024
The source saysIUCN Red List category: Least Concern (LC).Note: assessed 2024: the year in the assessment DOI (iucn.uk.2024-2) and the reference title

Source
05

Gibbs et al. 2000

Gibbs et al. (2000). Genetic evidence for female host-specific races of the common cuckoo. Nature.

The page saysA brood parasite whose females lay eggs that tend to match their hosts' eggs.
The source saysFemales of each race lay a distinctive egg type that tends to match the host's eggsNote: tagline
The page saysLays eggs that tend to match the host's, and barred underparts make some small birds treat it like a sparrowhawk
The source saysFemales of each race lay a distinctive egg type that tends to match the host's eggsNote: stats.superpower
The page saysThe species is split into host-specific races called gentes.
The source saysThe common cuckoo Cuculus canorus is divided into host-specific races (gentes).
The page saysbrown and spotted where meadow pipits are the host, plain blue where redstarts are
The source saysbrown and spotted for meadow pipit hosts or plain blue for redstart hosts
The page saysthese races follow the mother's line, while males mate across races and keep the cuckoo one species
The source saysgentes are restricted to female lineages, with cross mating by males maintaining the common cuckoo genetically as one species
The page saysEach race's females lay their own type of egg, which tends to look like their host's
The source saysFemales of each race lay a distinctive egg type that tends to match the host's eggs
The page sayseggs that tend to match its host's
The source saysFemales of each race lay a distinctive egg type that tends to match the host's eggsNote: vibe.reason

Source
06

Stoddard & Stevens 2010

Stoddard & Stevens (2010). Pattern mimicry of host eggs by the common cuckoo, as seen through a bird's eye. Proceedings of the Royal Society B: Biological Sciences.

The page saysfound that cuckoo races copy egg patterns more closely for hosts that reject foreign eggs more strongly
The source sayscuckoos have evolved better pattern mimicry for host species that exhibit stronger egg rejection
The page saysacross eight host species
The source saysquantify the level of pattern mimicry in eight host species of the common cuckoo
The page saysHosts fight back.
The source sayshost defences result in the evolution of host-egg mimicry in cuckoos

Source
07

Davies & Welbergen 2008

Davies & Welbergen (2008). Cuckoo-hawk mimicry? An experimental test. Proceedings of the Royal Society B: Biological Sciences.

The page saysbarred underparts make some small birds treat it like a sparrowhawk
The source sayssome small birds respond to common cuckoos Cuculus canorus as if they were sparrowhawks Accipiter nisusNote: stats.superpower
The page saysGreat tits and blue tits were alarmed by mounted cuckoos as much as by mounted sparrowhawks
The source saysGreat tits and blue tits were equally alarmed and reduced attendance at feeders during and after the presentation of mounted specimens of common cuckoos and sparrowhawks
The page sayscuckoos with barred underparts were treated like hawks while unbarred ones were treated like doves
The source sayscuckoos with barred underparts were treated like hawks, while those with unbarred underparts were treated like doves
The page saysbarred underparts that make tits treat it like a sparrowhawk
The source sayssome small birds respond to common cuckoos Cuculus canorus as if they were sparrowhawks Accipiter nisusNote: vibe.reason

Source
08

Marton et al. 2019

Marton et al. (2019). Host alarm calls attract the unwanted attention of the brood parasitic common cuckoo. Scientific Reports.

The page saysA brood parasite whose females lay eggs that tend to match their hosts' eggs.
The source saysavian brood parasites lay their eggs in the nests of other bird species, called hostsNote: tagline, brood parasite
The page saysit lays its eggs in the nests of other bird species, called hosts
The source saysavian brood parasites lay their eggs in the nests of other bird species, called hosts
The page saysGreat reed warblers that sounded the alarm more often suffered more parasitism
The source saysgreat reed warblers that alarmed more frequently experienced higher rates of parasitism
The page sayscuckoos in an experiment paid attention to those alarm calls
The source saysboth female and male common cuckoos Cuculus canorus pay attention to their host's, the great reed warbler's Acrocephalus arundinaceus alarm calls
The page saysEven a warning can backfire.
The source sayscan act in a detrimental manner by providing important nest location cues for eavesdropping brood parasites

Source
09

Merondun et al. 2024

Merondun et al. (2024). Evolution and genetic architecture of sex-limited polymorphism in cuckoos. Science Advances.

The page saysAdult males are gray.
The source saysadult males are monochromatic gray
The page saysFemales come in two plumages, gray or rufous
The source saysfemales exhibit either gray or rufous plumage
The page saysa 2024 genetic study traced that difference to the female-restricted genome
The source saysfemale plumage dichromatism maps to the female-restricted genomeNote: 2024 is the paper's publication year (Science Advances, reference metadata)
The page saysThe common cuckoo, Cuculus canorus, is a brood parasite.
The source saysThe brood parasitic common cuckoo ( Cuculus canorus )

Source
10

Davies & Welbergen 2009

Davies & Welbergen (2009). Social Transmission of a Host Defense Against Cuckoo Parasitism. Science.

The page saysreed warblers that watched neighbours mob a cuckoo increased their own mobbing
The source saysobservation of cuckoo (Cuculus canorus) mobbing by neighbors on adjacent territories induced reed warblers (Acrocephalus scirpaceus) to increase the mobbing of cuckoos
The page sayssocial learning lets hosts build up their defence quickly
The source sayssocial learning provides a mechanism by which hosts rapidly increase their nest defense against brood parasites

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.