European breeding distribution ranges for the pied flycatcher (Ficedula hypoleuca, light blue), the collared flycatcher (Ficedula albicollis, green), and regions where both species occur together (red). Unreservedly redrawn and adapted from range maps in Cramp & Perrins . Circles indicate sampling sites and the number of birds collected on each site is given within the circle. Numbers for pied flycatchers are in blue font and numbers for collared flycatchers are in green font.
Backström et al. BMC Evolutionary Biology 2013 13:2 doi:10.1186/1471-2148-13-2