Dunnock

The dunnock (Prunella modularis) is a small accentor found across much of Europe and western Asia. Adults are about 13.5–14.5 cm long and weigh around 21 g. The plumage is subdued but finely patterned: the head and breast are grey, the upperparts warm brown with dark streaking, and the slender pointed bill is adapted to picking small invertebrates rather than cracking large seeds.

Despite the old English name “hedge sparrow”, the dunnock is not a true sparrow but belongs to the accentor family, Prunellidae. Its low, shuffling feeding style and preference for dense cover make it easy to overlook except in spring, when males sing from more exposed perches.

Dunnocks are strongly associated with dense vegetation close to the ground. They occur in scrub, hedgerows, woodland undergrowth, forest edges, gardens, parks and young conifer plantations, using cover both for feeding and concealment.

They usually forage on or very close to the ground, so habitats with a mixture of low vegetation, leaf litter and sheltered edges are especially suitable.

The diet changes with the seasons. In spring and summer, insects, spiders, worms and other small invertebrates dominate. Seeds become increasingly important from late summer through winter as invertebrate availability falls.

A study published in 1986, carried out in hedgerows in Shropshire, England, found beetles and other arthropods prominent in the summer diet, while seeds were taken mainly from August into spring.

Migration varies markedly across the range. Many birds in western and southern Europe are resident, while populations breeding farther north and east are more strongly migratory and move into western, central and southern Europe for winter. Spring and autumn movements therefore mix resident birds with migrants across much of the continent.

Dunnocks have one of the most flexible mating systems among familiar European songbirds. A breeding group may be monogamous, involve one male with several females (polygyny), one female with two or more males (polyandry), or several males and females sharing mating access (polygynandry). Classic field studies showed that this variation is partly shaped by how females' home ranges are distributed and how easily males can monopolise access to them.

Sperm competition is correspondingly intense. Before copulation, a male may peck at the female’s cloaca and stimulate her to eject sperm from a previous mating, increasing his own chance of fertilisation. In groups with two males, the subordinate male is more likely to help feed the chicks when he has also gained mating access, and DNA studies have shown that male parental effort is closely related to the likelihood of paternity.

The female builds a neat cup nest low in dense shrubs, hedges or other vegetation. The nest is built on a loose platform of twigs and consists mainly of moss and grass, often lined with hair, grass or a few feathers. A typical clutch contains 4–5 eggs, which she incubates for about 14–15 days. The chicks are altricial and normally remain in the nest for roughly another 12–14 days, while one or more males may help the female feed them. Two broods in a season are common.

Dunnocks were deliberately introduced from England into several parts of New Zealand between 1865 and 1896. Acclimatisation societies released them partly because settlers hoped insect-eating birds would help control pests in orchards. The species became naturalised and is now widespread, especially in southern New Zealand, where it occurs in gardens, farmland, scrub and forest edges.

No negative effects on native species are currently known in New Zealand, although dunnocks have spread beyond heavily modified landscapes and now occur on remote island groups including the Chatham, Antipodes, Auckland and Campbell Islands. The New Zealand population therefore provides a striking example of how successfully the species can establish when suitable low, dense vegetation is available.

The dunnock is classified as least concern on the IUCN Red List and is also assessed as Least Concern in Europe. It remains widespread and numerous, although population trends differ between regions.

In Britain, the breeding population declined by 43% between 1967 and 2024, with the sharpest fall during the 1970s and 1980s. Numbers recovered somewhat from the late 1990s before declining again in recent years. Low winter food availability may have contributed to the earlier decline.