Eurasian reed-warbler  (Acrocephalus scirpaceus)

The Eurasian reed warbler is classified as Least Concern (LC) on the IUCN Red List (1).

The Eurasian reed warbler (Acrocephalus scirpaceus) is a rather indistinct, plain, un-streaked warbler (2) (3). There is little to distinguish this bird from other warblers (4), the upperparts being dull olive-brown, with a darker patch on the crown, a cream eye stripe and a dusky patch between the eyes and the bill. There is a faint rusty tinge to the back of the head, wings and tail and the whitish underparts are suffused with pale buff on the breast and darker buff on the flanks. The juvenile Eurasian reed warbler is brighter and rustier than the adult, with an orange suffusion on the upperparts and duskier underparts (2). 

The eye colour of the Eurasian reed warbler changes with age and the iris is charcoal coloured in their first year, but olive-brown when maturity is reached. Young birds also have spots on their tongues, which presumably helps guide feeding parents to the young’s mouth (5). 

The Eurasian reed warbler is robustly built, with bluntly pointed wings, a large bill and large feet that allow it to clamber about reeds with ease and confidence (6), even enabling it to grip vertically onto reed stems whilst looking for insects (3).

A migratory species, the Eurasian reed warbler breeds from western Europe across to western Russia, the Caspian area, Iran, southeast Kazakhstan and extreme northwest China, and travels to sub-Saharan Africa before the onset of winter (2) (7).

As its common name implies, the Eurasian reed warbler primarily breeds in mature reed beds along the shores of lakes, fish ponds, ditches and rivers, although it also breeds in other vegetation in drier habitats, such as scrub. In its wintering grounds it occurs in thickets and tall grass, as well as bushes, forest edges and garden hedges (2).

A rather opportunistic species, the Eurasian reed warbler feeds on a varied diet that consists primarily of a diversity of insects, but also includes fruits, seeds and flowers. It mainly catches its prey on reed stems and blades, in bushes and on the ground (2). 

In Europe the Eurasian reed warbler breeds between May and August, with monogamous pairs constructing their nest in loose colonies. It is the female that mainly builds the deep, cup-shaped nest by neatly weaving split reed blades, flowers, grass stems and plant down. Three to five eggs are laid and then incubated by both adults for 8 to 13 days. The chicks are fed by both parents and fledge from the nest after 10 to 12 days, becoming independent 10 to 14 days later (2). 

The Eurasian reed warbler is a common victim of the European cuckoo (Cuculus canorus), a brood parasite that lays its eggs in the nests of other species. The cuckoo deposits a single egg in the Eurasian reed warbler’s nest and the cuckoo chick hatches first, so that it can remove the other eggs from the nest. The adult Eurasian reed warblers feed the cuckoo chick at the same rate at which they would feed their brood of three or four, such that the cuckoo rapidly grows and soon dwarfs its unwitting foster parents. This parasitism can reach such high levels that Eurasian reed warbler populations begin to decline, meaning the European cuckoo must switch to another host species (6).

With an extremely large range and a large population, the Eurasian reed warbler is not currently considered at risk of extinction (8). There are no known major threats to this species, and most populations in Europe, which comprises over half of its breeding range, are thought to be stable or slightly increasing (9). In some parts of its range, the Eurasian reed warbler has benefited from the eutrophication or rivers, which increases the growth of reed beds. However, in other parts of its range it has been adversely affected by the reclamation of marshes (2).

The Eurasian reed warbler has not been the target of any known conservation measures.

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More information on the Eurasian reed warbler and other bird species:

• BirdLife International:
  http://www.birdlife.org/