Sedge warbler (Acrocephalus schoenobaenus)
|French:||Phragmite des joncs|
|Size||Length: 11.5 - 13 cm (2)|
Wingspan: 19 cm (3)
|Weight||c. 12 g (3)|
- The sedge warbler is a small, rather plump brown bird with a conspicuous cream-coloured stripe above the eye.
- Interestingly, the sedge warbler is capable of inserting random phrases into its complex song, ensuring that it never sings the same tune twice.
- For such a small bird, the sedge warbler migrates an incredible distance, travelling around 3,860 km between its breeding and its wintering grounds.
- As well as being used to find a mate, the song of the sedge warbler is used to defend territories against rival males.
The sedge warbler is classified as Least Concern (LC) on the IUCN Red List (1).
The sedge warbler (Acrocephalus schoenobaenus) is a small, rather plump brown bird. Its upperparts are streaked with black (4), while the rump and uppertail-coverts are warm, tawny-brown and largely unstreaked (5). This species has a bold, striking cream-coloured stripe above the eye (4) (6). Also known as a ‘supercilium’, this stripe extends back and tapers above the rear of the ear-coverts, and becomes even whiter during the breeding season (5).
The underparts of the sedge warbler are creamy white (4) and the legs are greyish-brown (4) (6). This species has a relatively short, rounded, blackish-brown tail, and a short pointed beak (5) which probably earned the sedge warbler its genus name, Acrocephalus, which means ‘pointed head’ in Latin (3).
Juvenile sedge warblers have more of a yellowish-buff colour on the supercilium, as well as on the underparts, and the lower throat is speckled with small, dark brown spots. Although juvenile sedge warblers also have the contrasting tawny-brown rump, the rest of the upperparts tend to be more buffy in colour than in the adults (5).
The sedge warbler has a highly varied song that can be vigorous and complex (5), and at times harsh and grating (5) (7). The song consists of buzzing ‘churrs’ with chattering passages and the occasional sweet, clear whistle. The sequence usually lasts from around 20 to 40 seconds, but can sometimes be over a minute long, and is followed by a short pause of around one or two seconds before the next song begins (5). This species is known to be a good mimic (3) (7) (8), imitating other birds such as great tits (Parus major) and blackbirds (Turdus merula) (7) (8).
The range of the sedge warbler during the breeding season is extensive, covering most of Europe and extending as far as northern Scandinavia (7) and eastwards to central Siberia (5). The sedge warbler is a summer visitor to Britain, and can be found across most of the UK between April and October (4).
The entire breeding population of the sedge warbler winters in sub-Saharan Africa (4) (5) (7). This migration means the sedge warbler must fly around 3,860 kilometres to reach its destination, an impressive distance for such a small bird (7).
The sedge warbler breeds mainly in lowlands and valleys, tending to be found in cool, moist areas (5). It usually nests near water among the drier edges of reeds and sedge fens (3) (4) (5) (7), or in damp wetlands (4), including marshes (3). The sedge warbler is commonly found near ponds (5), and occurs from sea level to elevations of 1,900 metres (6).
This species is also known to occur away from areas of water, being found in habitats such as hedgerows, nettle beds and sites containing arable crops (5) (7). However, in such areas this species tends to avoid sites containing trees and tall bushes (5).
During the winter and when on migration, the sedge warbler is typically confined to sites near water or to areas of open wetland with emergent vegetation (5).
Although the sedge warbler is mainly insectivorous (3) (4) (5), it may also feed on some plant material, such as berries, during the autumn and winter (3) (4). The sedge warbler mainly hunts its prey at dawn or dusk when the temperature is lower, and it takes advantage of the insects’ sluggish behaviour at this time (8).
Typically solitary outside of the breeding season, the sedge warbler may form small, temporary groups when on migration, particularly in areas of abundant food (5). Large fat reserves are needed for the long migration, and this allows for unbroken flight for the heaviest birds (7). In autumn, the sedge warbler will mainly build its fat reserves by feeding on large numbers of plum reed aphids (Hyalopterus pruni) (5).
Male sedge warblers tend to arrive at the breeding grounds a couple of weeks before the females, and immediately select territories in which to pair and nest. Although this species is typically monogamous, the male sometimes pairs with a second female, either simultaneously or successively (5). The song of the sedge warbler is performed mainly to attract a mate, and once the male is paired it will revert to producing a short, low-intensity song (5). However, the sedge warbler’s song has been found to serve a dual function, as it can also be directed at rival males as a means of territorial defence (9).
The male sedge warbler usually perches on the top of a reed stem or bush during song (5), but a specialised song flight often separates and punctuates these performances. During this flight the bird will rise steeply into the air, then turn rapidly and make a slow spiral descent with its wings and tail outspread (5) (7). The song is generally performed from before sunrise until after sunset (5), but can also frequently be heard at night (7). Amazingly, by adding phrases into its song at random, this species is thought not to sing the same tune twice (3), and female sedge warblers are known to select males that have more complex songs and larger repertoires (10).
The nest of the sedge warbler is usually constructed near water, and is made from grass and moss with a horsehair and willow down lining (7). The female sedge warbler usually lays around 5 (3) (5) or 6 eggs (5), which are laid between May and June (5) and incubated for approximately 14 days (3). Although incubation is mostly carried out by the female, the male sedge warbler does assist in caring for and feeding the young once they have hatched. The fledglings leave the nest after 13 to 14 days, but continue to beg for food from the adult birds for a further 2 weeks (5).
The sedge warbler population is in decline (8) (11), and this is thought to be a result of drought in the species’ wintering range (11).
There are currently no conservation efforts known to be in place specifically for the sedge warbler, although this species is listed on Annex II of the Convention on Migratory Species (CMS or Bonn Convention) and on Annex III of the Bern Convention, which should offer it some protection (3).
Find out more about the sedge warbler and its conservation:
BirdLife International - Sedge warbler:
RSPB - Sedge warbler:
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- Coverts: small feathers concealing the bases of larger flight feathers, usually on the wings or tail.
- Ear-coverts: the circle of small feathers covering the ear opening of a bird. Also called auriculars.
- Emergent: aquatic plants whose stems and leaves extend beyond the water’s surface.
- Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
- Incubate: to keep eggs warm so that development is possible.
- Incubation: the act of incubating eggs; that is, keeping them warm so that development is possible.
- Insectivorous: insect-eating.
- Monogamous: having only one mate during a breeding season, or throughout the breeding life of a pair.
- Territorial: describes an animal, a pair of animals or a group that occupies and defends an area.
- Territory: an area occupied and defended by an animal, a pair of animals or a group.
IUCN Red List (June, 2013)
- Mullarney, K., Svensson, L., Zetterström, D. and Grant, P.J. (1999) Collins Bird Guide. HarperCollins Publishers Ltd, London.
BTO - Sedge warbler (June, 2013)
RSPB - Sedge warbler (June, 2013)
- Kennerley, P. and Pearson, P. (2010) Reed and Bush Warblers. Christopher Helm Publishers, London.
- Stevenson, T. and Fanshawe, J. (2004) Birds of East Africa. A&C Black Publishers, London.
Birds of Britain - Sedge warbler (June, 2013)
BBC Nature - Sedge warbler (June, 2013)
- Brumm, H., Robertson, K.A. and Nemeth, E. (2011) Singing direction as a tool to investigate the function of birdsong: an experiment on sedge warblers. Animal Behaviour, 81(3): 653-659.
- Airey, D.C., Buchanan, K.L., Szekely, T., Catchpole, C.K. and DeVoogd, T.J. (2000) Song, sexual selection, and a song control nucleus (HVc) in the brains of European sedge warblers. Journal of Neurobiology, 44(1): 1-6.
BirdLife International - Sedge warbler (June, 2013)