Sedge warblers are wetland migrants that breed in dense waterside vegetation and must accumulate substantial fat reserves before migration to cross the Sahara in a single flight.
Sedge warbler welfare before migration requires access to dense wetland vegetation with abundant invertebrate prey for fattening. Drainage of wetland margins and loss of waterside scrub reduces both breeding habitat and pre-migratory foraging areas. The physiological demands of trans-Saharan migration leave no margin for poor pre-migratory body condition.