Although a common bird in the UK, only recently have studies shown that the dunnock has an interesting domestic arrangement. Although the pair-bond between the birds appears strong during the breeding season, females will often court another male and mate with him. This ensures that her chicks – whichever partner actually sires them – will receive an adequate supply of food from both males. The nest is hidden in a hedge or shrub and contains up to five pale blue eggs. There can be up to three clutches laid in a season, the first appearing in March or April. Incubation takes about two weeks with the female taking sole charge of the brooding. The young are fed by both sexes and fledge after some 12 to 14 days. The dunnock is primarily an insect feeder although small seeds often form part of the bird’s diet as well.
In the south of England, the dunnock is the principal host of the cuckoo (Cuculus canorus). Although cuckoos also parasitise the nests of meadow pipits, and match their eggs to those of that host, they rarely produce blue eggs to match those of the dunnock. This does not seem to stop dunnocks becoming unwitting foster parents to the much larger cuckoo, and faithfully rear the interloper as their own young. The cuckoo chick has a much greater appetite than the young dunnocks so, for this reason, after it hatches the cuckoo chick evicts the dunnock eggs or chicks from the nest to remove the competition for food.