Detailed analyses of the biometrics of white-spotted bluethroats captured in the Iberian Peninsula and sub-Saharan Africa show that previous criteria for diagnosing subspecies are inadequate. This deficiency seems to result from feather wear during the breeding period and so new criteria are proposed for the migratory and wintering periods. Foreign recoveries in Portugal indicate that the new criteria work better during these periods but, a small proportion of misidentifications are still likely to occur. As bimodality is shown by biometric traits other than wing length, further refinements should consider the use of multiple traits as well as genetic markers.