bluethroat, (Erithacus svecicus or Luscinia svecica), Eurasian chat-thrush of the thrush family, Turdidae (order Passeriformes). The bluethroat is aobut 14 centimetres (5 1/2 inches) long and has a bright blue throat, incorporating a crescentic spot of red or white, depending on the subspecies. Found from western Europe eastward to western Alaska, the bluethroat is essentially a bird of damp thickets in mountains, but in western Europe it occurs in lowlands also. It has a rich, varied, warbling song.