# Cuckoo — Facts, Threats & Conservation

*Cuculus canorus (Linnaeus, 1758) — family Cuculidae*

> The common cuckoo (Cuculus canorus) is a brood-parasitic migrant whose male's two-note call marks British spring; females lay in other birds' nests, and British breeding numbers have declined steeply — Red-listed — linked to caterpillar loss and migration pressures.

**IUCN status:** Least Concern globally — Red-listed in Britain after steep breeding decline  ·  **WARN range:** Breeds across Europe and Asia to Mongolia, Winters in sub-Saharan Africa; summer visitor to Britain

## Quick facts
| Fact | Value |
| --- | --- |
| Call | Male: two-note 'cuck-oo' — April to June |
| Breeding strategy | Brood parasite — lays in host nests |
| UK status | Red-listed; steep decline |
| Diet | Hairy moth caterpillars |
| Migration | Britain to sub-Saharan Africa |
| Common hosts | Meadow pipit, dunnock, reed warbler |
| Habitat | Heath, rough grassland, marsh edge with hosts nearby |

## Scientific classification
- **Kingdom:** Animalia
- **Phylum:** Chordata
- **Class:** Aves
- **Order:** Cuculiformes
- **Family:** Cuculidae
- **Genus:** Cuculus
- **Species:** Cuculus canorus

## Conservation status
- **Status:** Least Concern
- **Population:** Wide Eurasian range; steep decline as British breeder
- **Trend:** Decreasing in Britain; variable elsewhere
- **Assessed:** 2019
- **CITES:** Not listed
- Red-listed in Britain. Decline linked to caterpillar food loss, migration mortality and wintering-ground pressures.

## Key facts: Cuckoo
- Male cuckoos call 'cuck-oo' from April to June — the sound of spring in much of Britain.
- Females lay eggs in other birds' nests; the cuckoo chick evicts host young and is raised by foster parents.
- British breeding cuckoos are Red-listed after steep decline — range contracting north and west.
- Adults depend heavily on hairy moth caterpillars — loss of rough grassland and hedgerow moths hits cuckoos.
- Winter in sub-Saharan Africa; migration routes cross the Mediterranean and Sahara.
- Different cuckoo races target different host species — meadow pipit, dunnock, reed warbler.
- Hearing a cuckoo is increasingly a regional experience — upland and northern Britain hold most callers.

## Brood parasitism — the nest you never built
A female cuckoo watches host nests, waits until the host is absent, removes one host egg if time allows, and lays a single egg that mimics the host's colour and pattern — in some races convincingly, in others less so. The host incubates; the cuckoo egg hatches quickly; the chick pushes other eggs and chicks from the nest using a hollow in its back specifically adapted for the task.

Foster parents feed the cuckoo chick until it fledges at enormous size — a reed warbler feeding a cuckoo chick several times its own mass is one of ornithology's starkest images. Host species evolve rejection behaviour — ejecting alien eggs — and cuckoos evolve better mimicry; the co-evolutionary arms race continues.

In Britain, meadow pipits, dunnocks and reed warblers are common hosts. Different cuckoo gentes — host-specific lineages — lay eggs matching particular host species. Not every cuckoo egg succeeds; hosts that recognise and reject parasitic eggs reduce cuckoo breeding success locally.

Cuckoo eggs vary by host race — reed warbler eggs are green and speckled to match reed warbler clutches; meadow pipit eggs differ. Host rejection behaviour varies too — reed warblers eject some parasitic eggs; dunnocks accept many. The arms race plays out differently in each host-cuckoo pairing across Britain.

Cuckoo chicks do not evict host eggs in every nest — success rate varies by host attentiveness and egg mimicry quality. Failed parasitism is common; cuckoo decline reduces pressure on host populations but also removes a species that shaped host evolution for millennia.

Young cuckoos leave the foster nest and are fed by foster parents for weeks — the parasitic chick outgrows the nest structurally and may sit on rim while still demanding food from smaller hosts. The size mismatch is among the starkest in bird behaviour.

## The call, the migration and the caterpillar link
Male cuckoos establish territories by call from April — the classic two-note song advertising fitness to females and rivals. Females call less conspicuously but produce a rich bubbling display. Cuckoos are birds of open country with scattered trees — heath, marsh edge, upland fringe — not dense woodland.

After breeding, cuckoos migrate to sub-Saharan Africa — a journey crossing the Sahara and Mediterranean, with hunting and drought on migration routes documented as mortality sources. Satellite tracking has revealed wintering areas in the Congo basin and migration timing that varies individually.

Adult cuckoos feed mainly on hairy caterpillars — especially moth larvae of rough grassland and heath. Decline in large hairy moth populations through agricultural intensification, pesticide use and habitat loss correlates with cuckoo decline. The bird at the top of that insect food chain is an indicator that moth-rich rough ground is disappearing.

Male cuckoos compete for display territories where females hear them — a loud male in open country attracts females that then search nearby for host nests. Cuckoo decline reduces not only the call people know but the parasitic pressure on host populations — meadow pipit and reed warbler nesting success can shift when cuckoos disappear from an area.

Cuckoo decline on Dartmoor, Welsh uplands and Scottish margins follows regional moth and host abundance — strongholds correlate with rough grassland and reedbed where hosts remain common and caterpillar food persists.

## British decline — Red list and contracting range
Cuckoo breeding numbers in Britain fell substantially from the 1980s onward — one of the steepest declines of any formerly widespread summer visitor. The species is Red-listed. Range has contracted from much of lowland England and Wales toward upland areas, Scotland and western margins where rough grassland and heath persist.

Multiple causes operate: caterpillar food loss on breeding grounds, conditions on African wintering grounds, migration mortality, and potentially phenological mismatch if host nesting advances faster than cuckoo arrival. No single factor explains the trend; the cumulative pressure on a long-distance migrant with specialised diet and parasitic breeding is severe.

Silence where cuckoos once called is noticed by older rural residents before it appears in national statistics — the bird whose call defined spring is becoming a regional sound. Conservation action targets rough grassland, moth habitat, migration route protection and wintering ground forest retention in Africa.

Satellite tracking showed cuckoos take different migration routes and timing — some cross the western Mediterranean, others the eastern. Mortality on migration is substantial; drought and hunting pressure on stopover and wintering grounds add to breeding-ground caterpillar loss as cumulative decline drivers.

Pesticide reduction on farmland margins and hedgerows supports moth larvae that cuckoos eat — general invertebrate recovery on breeding grounds aligns with cuckoo needs without targeting the species directly at garden feeders.

## What helps cuckoos — beyond the clock
Cuckoos cannot be helped at a garden feeder — they need landscape-scale rough grassland, heath and hedgerow producing moth caterpillars, plus host birds nesting successfully nearby. Allowing bracken, gorse and rough pasture on farmland margins, reducing pesticide drift onto hedgerows and supporting upland heath management all align with cuckoo needs.

Reporting cuckoo calls to annual bird surveys contributes population data that tracks decline and recovery. The call is easy to identify — two equal notes — and survey schemes rely on public records.

The cuckoo is Least Concern globally because of a wide Eurasian range, but the British story is regional collapse of a cultural icon — a brood parasite whose spring call masked a dependency on moths, hosts and African forest that everyday farmland change eroded faster than the bird could adapt.

Reporting cuckoo arrival dates to annual bird surveys builds the phenology dataset that tests whether cuckoos still arrive when hosts are nesting. Mismatch — cuckoos arriving after host clutches are complete — reduces parasitic success and may accelerate decline in southern Britain where hosts nest earlier in warming springs.

Clocks and folklore tied cuckoo arrival to spring labour — hay timing, planting dates, seasonal markers. That cultural calendar broke when cuckoos stopped calling, not when clocks changed.

## What WARN does
WARN publishes free, sourced species education for farmland birds whose decline people hear before surveys confirm it. The cuckoo is Red-listed in Britain — spring's call fading where moth-rich rough ground disappeared.

If this guide helps you understand wildlife and the pressures it faces, a gift to WARN supports habitat protection and free public education in our partner countries.

## Frequently asked questions: Cuckoo
### Why do cuckoos lay eggs in other birds' nests?
Cuckoos are brood parasites — females do not build nests or raise chicks. Host parents incubate the egg and feed the cuckoo chick, which evicts their own young. It is an evolutionary strategy, not laziness.

### When do cuckoos arrive in Britain?
From April onward, with peak calling in May and June. They leave for Africa from July into August. Timing varies by latitude — Scotland later than southern England.

### Are cuckoos declining in Britain?
Yes, sharply. Red-listed with substantial breeding decline since the 1980s and range contracting north and west. Loss of caterpillar food and migration pressures are among documented causes.

### What do cuckoos eat?
Common Cuckoos eat Hairy moth caterpillars. The common cuckoo (Cuculus canorus) is a brood-parasitic migrant whose male's two-note call marks British spring; females lay in other birds' nests, and British breeding numbers have declined steeply — Red-listed — linked to caterpillar loss and migration pressures.

### Which birds raise cuckoo chicks?
In Britain, commonly meadow pipit, dunnock and reed warbler — depending on region and cuckoo race. The foster parents feed the chick until it fledges much larger than themselves.

### Where do cuckoos winter?
Sub-Saharan Africa, mainly forest and woodland areas in the Congo basin and similar regions. Migration crosses the Sahara and Mediterranean.

### Where do cuckoos live?
In Britain, cuckoos breed on heath, rough grassland and marsh edges where host birds such as meadow pipits, dunnocks and reed warblers nest nearby. Males call the two-note 'cuck-oo' from April to June. British breeders are Red-listed after steep decline, though the species remains Least Concern across its wider Eurasian range.

### Are cuckoos dangerous?
Cuckoos are not dangerous to people. They are brood parasites that lay eggs in other birds' nests, but they pose no physical threat to humans. Adults feed mainly on hairy moth caterpillars from rough grassland and heath. British breeding numbers have declined sharply, with the species Red-listed as range contracts north and west.

### How long do common cuckoos live?
A precise wild lifespan for common cuckoos is not firmly established in the sources cited on this guide. The common cuckoo (Cuculus canorus) is a brood-parasitic migrant whose male's two-note call marks British spring; females lay in other birds' nests, and British breeding numbers have declined steeply — Red-listed — linked to caterpillar loss and migration pressures. Where longevity figures appear in the literature they vary by region, sex and whether animals are wild or captive.

## Sources
- [IUCN Red List — Cuculus canorus](https://www.iucnredlist.org/species/22683873/167509412)
- [BTO — BirdFacts: Cuckoo](https://www.bto.org/understanding-birds/birdfacts/cuckoo)

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Full guide: https://worldanimalrescuenetwork.org/wildlife-guides/cuckoo