This warbler can be difficult to distinguish from reed warblers. Marsh warbler adults have green/brown upperparts with black tips to the wing feathers. The head and cheeks are the same colour as the back with an almost yellow eye stripe sometimes visible. Their underparts are a lighter buff colour with an almost white throat. Their song can be hard to distinguish due to the males' impressive mimicry ability.
Average Length: 13 -15 cm
Average Lifespan: 2 Years
Average Wingspan: 18 - 21 cm
Their diet is nearly exclusively insects, but they occasionally eat berries in the autumn. They usually pick insects off vegetation but can be seen taking insects in the air or on the ground. You are unlikely to see them at garden feeders due to the low population.
Breeding begins in the second half of May with the building of a deep, cylindrical cup-shaped nest out of stems, grasses and other plants, supported by plant stems, usually less than 1m of the ground. 3-6 glossy pale blue eggs are laid and incubated by both the male and female for around 2 weeks. After hatching both parents feed the chicks for another 10-11 days. Their breeding season ends in June which means they only produce one brood per season.
The reasons for the steep declines in this species are not well understood, however historical disturbance by bird watchers and egg collectors likely had a significant effect on the already small population. The loss and fragmentation of suitable habitat is one of the reasons this species has become so scarce. Furthermore, climate change is thought to have driven declines in this population by causing drought and food shortages in their over-wintering grounds. The small population in the UK are susceptible to chance events, such as extreme weather, that occur in their breeding grounds or during migration. Furthermore, the size of the population means they will struggle to recover, due to decreased immigration, even with conservation efforts. The small population makes scientific study in the UK very difficult.
Reporting sightings of this bird, especially during the breeding season.
Petitioning local areas to protect grassland and reedbed habitats.
Do not disturb this bird if you are trying to catch a glimpse.
Marsh warblers are expert mimics and was the first bird that was found to mimic other birds from both their summer and winter grounds.
BirdLife International (2023) Species factsheet: Acrocephalus palustris. Downloaded from http://datazone.birdlife.org/species/factsheet/marsh-warbler-acrocephalus-palustris. Accessed:11/09/2023.
Both, C., Van Turnhout, C. A. M., Bijlsma, R. G., Siepel, H., Van Strien, A. J., & Foppen, R. P. B. (2010). Avian population consequences of climate change are most severe for long-distance migrants in seasonal habitats. Proceedings of the Royal Society B: Biological Sciences, 277(1685), 1259–1266. https://doi.org/10.1098/RSPB.2009.1525
British Trust for Ornithology (2023) Marsh warbler, BTO. Available at: https://www.bto.org/understanding-birds/birdfacts/marsh-warbler (Accessed: 11 September 2023).
RSPB (2023) Marsh warbler bird facts: Acrocephalus palustris, The RSPB. Available at: https://www.rspb.org.uk/birds-and-wildlife/wildlife-guides/bird-a-z/marsh-warbler/. Accessed:11/09/2023.