page_title: Sedge warbler
section_title: Breeding
hierarchical_section_title: Sedge warbler / Behaviour / Breeding
caption_attribution_description: English: Sedge warbler (Acrocephalus schoenobaenus), male, Otmoor, Oxfordshire
context_page_description: The sedge warbler is an Old World warbler in the genus Acrocephalus. It is a medium-sized warbler with a brown, streaked back and wings and a distinct pale supercilium. Sedge warblers are migratory, crossing the Sahara to get from their European and Asian breeding grounds to spend winter in Africa. The male's song is composed of random chattering phrases and can include mimicry of other species. The sedge warbler is mostly insectivorous.
context_section_description: Male sedge warblers commence singing only a few hours after arriving on their breeding territory. The song is given from a bare perch such as a reed stem or bush, or from cover and during routine flights within their territory. Song-flights are also performed: while singing, the bird takes off, rises to a height of around 2–5 metres and then after a short circling flight, makes a slow, 'parachuting' descent, often with the wings held up in a 'v' shape. The song has the function of attracting a mate, rather than keeping other males away, and is stopped as soon as a mate is found. Contact calls are described as chirr or kerr; these calls are repeated quickly to form a rattling alarm call.
  Studies have found that early-arriving males occupy the best breeding territories. A study in Nottinghamshire, England, showed that a third of males which returned bred within 50 m or less of their previous breeding site, and only 14% bred further than 400 m away. Another study conducted in the Nida River valley in Poland showed that individual males tend to show the biggest shifts in territory location in the first two seasons of life (up to >400 m). This seems to be caused by an increasing early arrival on the breeding grounds in the first years. Hence, they find more potential territories left unoccupied by conspecifics upon arrival, causing them to shift to better quality ones. 
  Pairs are usually social monogamous, but not strictly so. Males commonly practice promiscuity, and part of the males settle a new territory and resume territorial behavior whilst the female incubates the first clutch. When successfully pairing with another female the male will usually take part in rearing both broods.
  If eggs or chicks are predated, the female will often leave the male, who then resumes singing and pairs with another female. Hybridisation with the Eurasian reed warbler has been recorded.
  The male defends a territory of around 0.1 to 0.2 hectares; in a study at Zaanstad, Netherlands, 68 territories were studied, with an average size of 1064 metres square one year, and 904 m sq the next. The nest, built by the female, is in vegetation on the ground or up to a height of 50 cm. The cup-shaped structure has an outer layer of grass, stems and leaves, plus spiders' webs, with a thick, finer layer inside including reed flowers, animal hair and plant down. It is woven around vertical plant stems. Between 3-5 greenish-yellow and brown-mottled eggs are laid, measuring 18 x 13 mm and weighing 1.6 g each. They are incubated by the female for 14 days; the chicks are altricial and naked. Both male and female care for the chicks, which fledge after 13–14 days. After leaving the nest, young sedge warblers continue begging for food from their parents for between 1–2 weeks after learning to fly.
caption: singing
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