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Acrocephalus palustris
Seen only very occasionally in the UK, the marsh warbler is a long-distance migrant, breeding across central and eastern Europe and spending winters in south-eastern Africa. Sightings in Britain are limited to coastal areas, where up to only around 8 pairs are recorded as breeding each year.
Marsh Warbler
Marsh Warbler singing from a perch
Marsh Warbler hidden in the long grass
Marsh Warblers are a highly vocal bird species, and have a very distinctive call
Length:
13cm to 15cm
Wingspan:
18cm to 21cm
Weight:
10g to 15g
Marsh warblers are small brownish warblers, similar in appearance to the more common reed warbler and often their song is the best way to distinguish between the species.
Marsh warblers have an olive-brown back, nape and crown, with a greenish-brown rump and pale brown tail. Wings are also olive-brown, but tipped with darker black-brown feathers.
Facial markings of marsh warblers include a pale cream eye stripe, a white throat and chin, darkening into a yellowish-cream breast and belly, with yellow flanks.
Females and males are alike, with no obvious visual differences between the sexes. Both have pink legs, dark brown eyes, and a light grey bill.
Juvenile marsh warblers have similar markings and colouring to adult birds, although may have a bronze tinge to their plumage, and their legs are slightly darker.
Close up of a Marsh Warbler perched on a branch
At 13 cm (5.1 in), marsh warblers are the same size as their close relative the reed warbler. There is no difference in size between males and females, with both falling within the measurement ranges below:
Marsh Warbler pictured on a reedbed
Marsh warblers have a loud, distinctive warbling song, with flowing liquid notes and trills.
They are accomplished mimics and incorporate the songs of almost 100 other species into their own, and are thought to add more melodies to their repertoires each year, learned from spending time in mixed species groups on their wintering grounds in south-eastern Africa.
The diet of a marsh warbler is mainly insectivorous, with mayflies, damselflies, aphids, and lacewings gleaned from the underside of leaves as they probe the vegetation of their habitat. Snails, larvae, caterpillars and spiders are common prey. In autumn and winter, some berries may also be eaten.
Young marsh warblers are initially fed on soft regurgitated invertebrates and sometimes fruit by both parents.
Marsh Warbler in full song
Ideal habitats for marsh warblers include scrubby, grassland and reedbeds. Marshy vegetation on the edge of swamps, nettle beds and ditches are also popular choices.
Marsh warblers breed across Europe, from parts of southern England and northern and eastern France in the west, to southern Scandinavia in the north, and eastwards throughout Europe and Central Asia to Kazakhstan.
The southern limits of their breeding range encompass parts of Italy, the Balkans, eastern Turkey and north-west Iran.
In winter, the entire breeding population of marsh tits heads to Malawi, Mozambique, South Africa, Tanzania, Zambia and Zimbabwe.
Marsh warblers are common and widespread across much of northern Europe, with Germany having the highest population, with up to 520,000 pairs. Breeding is well established and relatively stable in high numbers across Lithuania, Latvia, Sweden, Estonia and France.
Marsh Warbler, pictured from behind
Marsh warblers are one of the UK’s rarest breeding birds, with only between 2 and 8 pairs nesting each year. Passage birds may be seen during migration, but confirmed sightings are scarce.
Established breeding sites of marsh warblers were once found in parts of Worcestershire but in the 21st century seem to be largely concentrated in south-east England, especially Kent.
They are relatively late arrivals, so the best time of seeing a temporary resident marsh warbler is between May and September.
There is perhaps a greater chance of spotting migrant birds in passage, from May to June and August to September, when sightings are possible along the entire eastern coast of Scotland and England.
Close up of a Marsh Warbler
Typical lifespan of a marsh warbler is 2 years, although the oldest known individual according to BTO records reached 7 years and 10 months.
As is typical of ground-nesting birds, crows and jays are among the top predators of marsh warblers and their young. Foxes, stoats and weasels will all opportunistically raid a nest.
Protected under the Wildlife and Countryside Act, 1981, marsh warblers are also given additional Schedule 1 protection, meaning as well as it being an offence to kill, injure or capture a bird of this species, their eggs, young and nest sites are also safeguarded.
In the UK, the number of breeding marsh warblers has witnessed a steep decline from 180 pairs at the start of the 20th century, falling to around 60-80 pairs by the 1970s.
Marsh warblers have Red status on the British Birds of Conservation Concern list, but elsewhere in Europe, populations are secure and stable, with an estimated 3.2 to 6.8 million pairs.
Marsh warblers have Red status on the British Birds of Conservation Concern list
Breeding marsh warblers choose a nesting spot in grass meadows, scrublands or marshlands, frequently located near water. The female builds a cup-shaped nest from dry grass lined with roots and soft plant parts.
Nests are usually built at ground level, putting them at greater risk of failure due to predation.
Marsh warblers lay between 3 and 6 pale blue, green, or grey eggs with olive or reddish-brown spots. Eggs are smooth and glossy, and measure 19 mm by14 mm (0.7 in by 0.6 in).
Incubation is undertaken by both the male and female on rotation for between 12 and 14 days. Hatchlings are fed by both parents in the nest for 10 to 11 days before they are ready to fledge.
Marsh warblers are usually monogamous for the duration of the breeding season and raise one brood together. Some polygamy does occasionally occur. Breeding takes place for the first time at one year of age.
The nest of a Marsh Warbler, with eggs inside
During the breeding season male marsh warblers will vocally defend their territories against threats. On their wintering grounds, they become more solitary, although may forage and migrate as part of larger mixed-species flocks.
All marsh warblers are migratory, leaving their breeding grounds in Europe and Central Asia once they have raised their young, and heading to wintering territories in south-eastern Africa.
Only a handful of marsh warblers breed in the UK each year, and once the breeding season ends, they all return to their wintering grounds in south-eastern Africa. There are no resident marsh warblers in Britain all year round, and the species is absent from the island or Ireland.
Marsh Warblers are a migratory species
Marsh warblers gather into mixed-species flocks during migration and spend time on their wintering grounds closely associating with other warblers and similar-sized songbirds.
With numbers of marsh warblers at such a dangerously low level, it’s unlikely that you’ll be lucky enough to attract one, but never say never!
They prefer tall, overgrown vegetation, with plants such as willowherb and nettles. A nearby water source is important, and a presence of aphids as a food source will also be appealing.
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