Moult extent differs between populations of different migratory distances: preliminary insights from Bluethroats Luscinia svecica

It is generally accepted that bird species/populations that migrate longer distances undertake less extensive moults than those that migrate shorter distances. First-year Bluethroats of two subspecies with different migratory distances (Luscinia svecica namnetum and L. s. cyanecula; the latter migrating the further of the two) were captured during the autumn migration period in 2012 in northern Iberia to test whether birds with longer migratory distances display less extensive post-juvenile moults than those that migrate less far. As predicted, the L. s. namnetum captured displayed more extensive moult in their greater coverts than the L. s. cyanecula but not in their tertials. However, due to the large degree of overlap between the two subspecies, moult extent does not seem to be a useful marker for separating these two subspecies.