Ecomorphological patterns in the Blackcap <i>Sylvia atricapilla</i>: insular versus mainland populations

<div><p><b>Capsule</b> Blackcap <i>Sylvia atricapilla</i> populations from the Azores archipelago show morphological differences to continental birds which are consistent with the ‘Island Rule’.</p><p><b>Aims</b> The morphology of insular vertebrates is usually the result of the evolution in their particular environment and leads to predictable morphological patterns, according to the Island Rule. We test the predictions of the Island Rule, using the Blackcap of the Azores archipelago as our model.</p><p><b>Methods</b> We compared morphological variation (body size and wing shape) of populations from the nine islands of the Azores to continental birds, using multivariate indexes. Also, we looked at the relationship between these patterns and possible insular ecological drivers of morphological divergence.</p><p><b>Results</b> Our findings are concordant with Island Rule predictions, as in general birds from the Azores are larger than continental populations, especially birds from the most distant islands. Wing shape also differs significantly, as Azorean Blackcaps tend to have rounder wings than continental birds with a migratory-like phenotype.</p><p><b>Conclusion</b> Overall, we conclude that the observed morphological patterns in Blackcap in the Azores conform in general to the Island Rule predictions.</p></div