Migratory Connectivity in European Bird Populations: Feather Stable Isotope Values Correlate with Biometrics of Breeding and Wintering Bluethroats Luscinia svecica

Understanding the migratory connectivity of migrant species is fundamental to their effective conservation. Analysis of individual traits that can vary geographically, such as biometrics and stable isotopic values of tissues, can help establish migratory connections. The bluethroat Luscinia svecica is a species of conservation concern in Europe (Annex I Birds Directive). Our aim was to identify the possible migratory connectivity of bluethroats Luscinia svecica breeding in central and western Europe (subspecies L. s. namnetum, L. s. azuricollis and L. s. cyanecula in part) with their wintering areas in southern Europe and Africa using biometric and stable isotopic (δ2H) analyses. Overall, the morphological and stable isotopes analyses provided two clusters of localities, one for the Atlantic French, Portuguese and Moroccan localities, corresponding to the breeding and winter quarters of L. s. namnetum, and another for the remaining localities (Spain, The Netherlands, Germany and Senegal), corresponding to the ranges of L. s. azuricollis and L. s. cyanecula. Migratory connectivity of L. s. namnetum is strong but it is much weaker for the other two subspecies. Biometric data were positively correlated to the stable isotope values, suggesting that the results derived from both methodological approaches lead to similar conclusions.