Brett Westwood searches for the reasons behind the declining numbers of many of our migrant songbirds - including the cuckoo, turtle dove and spotted flycatcher - and where the birds are most vulnerable. Speaking to researchers from the RSPB and British Trust for Ornithology, he explores the dual world of our migrants, like the pied flycatcher which spends its summers in the lush oak woods in the British Isles but winters in west African savannah woods. For some species, such as the cuckoo which evolved in Africa, northern Europe is a treasure trove of habitats and food supplies to be exploited, and many of our successful migrants are birds which originated in Africa but then moved north to cooler areas to breed. Do the reasons for them now being under threat lie here in the UK or south of the Sahara in their winter homes, and will they be able to evolve new wintering or summering areas to compensate for losses?