- Lifespan
- 3–4 years in the wild
- Size & Weight
- 32–34 cm, wingspan 55–60 cm; 110–140 g
- Habitat
- Open woodlands, scrubland, reed beds, and moorland edges across much of the UK, with a preference for areas supporting host bird populations.
- UK Distribution
- Summer visitor found throughout Britain and Ireland from April to September; arrives in late April and departs by August. Rare in upland areas.
- Diet
- Primarily large caterpillars, especially hairy species such as those of tiger moths, sawfly larvae, and other invertebrates; occasionally takes small birds' eggs.
- Prey
- Caterpillars (including hairy varieties), sawfly larvae, bugs, beetles, and other invertebrates
- Predators
- Sparrowhawks, tawny owls, hobbies, and occasionally jays; eggs and chicks preyed upon by crows, jays, and magpies
- Mating Season
- April to July
- Breeding
- No nest of its own; female lays 1 egg in nest of host species (primarily dunnocks, meadow pipits, and robins). Incubation period 10–13 days; fledging at 17–21 days. Single brood per season.
- Behaviour
- Solitary and secretive, though distinctive two-note call ('coo-coo') is highly audible. Obligate brood parasite that removes host eggs and relies entirely on foster parents to rear its chick. Males highly territorial and vocal.