This warbler breeds in eastern Europe and winters in West Africa. Its yellow crown stripe and yellow-brown streaked plumage help identify it.
It is more yellow-brown and streaked than similar warblers, with a distinct yellow crown stripe.
In Poland’s Biebrza Valley, researchers repeatedly counted singing Aquatic Warblers along 50 randomly placed one-kilometre transects during May and June from 2011 to 2013. The repeated transect method required 150 observer-days per year, compared with 175 for the traditional full count. Transects lay within 8,280 ha of suitable habitat and were at least 500 m apart.
Estimated abundance was highest at intermediate water levels and lowest on dry transects. Detection probability varied by year and was influenced by vegetation height and daily rainfall. The estimated power to detect a 20% population change over ten years was 68% for repeated transects, compared with 9% for raw counts.
An extinction-risk assessment has not been added yet.
In the Biebrza Valley breeding area, estimated Aquatic Warbler abundance was highest at intermediate water levels and lowest on dry transects. Water level and vegetation height are important local conditions when surveying this wetland bird.