Sedge warblers are migratory, crossing the Sahara to get from their European and Asian breeding grounds to spend winter in Africa.

The sedge warbler was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Motacilla schoenobaenus.

They can be easier to confuse with aquatic warblers due to an apparent pale central crown stripe contrasting with the darker edges.

[9] The oldest recorded sedge warbler was a bird ringed in Finland which reached the age of 10 years, 1 month.

Data analysis by the British Trust for Ornithology has shown that fluctuations in the sedge warbler population stem from the adult survival rate, due to changes in rainfall on the birds' wintering grounds.

[7] Loss of wetland areas for feeding on migration, and the expansion of the Sahara Desert, pose threats to the sedge warbler's breeding population.

[12] Birds begin leaving Africa in late February, fatten up at wetlands before and probably after crossing the Sahara, and arrive in Europe from March onwards.

[7] During the breeding season, this is a species found in reedbeds, often with scrub, ditches and habitats away from water including hedgerows, patches of stinging nettles, and arable crops.

Song-flights are also performed: while singing, the bird takes off, rises to a height of around 2–5 metres (6.6–16.4 ft) and then after a short circling flight, makes a slow, 'parachuting' descent, often with the wings held up in a 'v' shape.

After leaving the nest, young sedge warblers continue begging for food from their parents for 1 to 2 weeks after learning to fly.

[7] Prey taken by sedge warblers includes mayflies, dragonflies and damselflies, grasshoppers, bugs, lacewings, moths, beetles and flies.

In late July, prior to migration, it appears that sedge warblers seek out sites with large numbers of plum-reed aphids and stay there longer than at other places; ringing studies show that birds may move considerable distances (e.g. from southern England to northern France) in search of food before beginning their actual migration.

In Portugal, the aphid supply dries up too early for sedge warblers to utilise it, so many birds do not stop off there and are already heavy with fat when they pass through.

Birds with the heaviest fat reserves built up before migration are capable of non-stop flights from Africa to southern Britain, or from Uganda to Iraq, for example.

A study at Attenborough, Nottinghamshire in England, found that the habitats used for foraging during the breeding season were 47% marshland, mostly Glyceria grasses, 26% shrub, 21% field vegetation and 6% woodland.

Sedge warblers tend to hop between plant stems and pick insects from underneath leaves; they take advantage of the low temperatures around dusk and dawn which make their prey less mobile.