Atypical song of Blackcap Sylvia atricapilla

The song of the Eurasian Blackcap Sylvia atricapilla consists of two distinct parts: an initial chattering of different harsh notes followed by a louder, fluting warble. However, some enigmatic individuals present an atypical version of their song characterised by a remarkable simplification of the traditional rich fluting warble. This study documents the unprecedented observation in the Iberian Peninsula of an atypical singer in Els Ports Natural Park (Catalonia, NE Spain). This bird exhibited distinct behavior including perching high in trees and intense morning singing, in addition to the atypical song marked by the substitution of the rich fluting warble by a monotonous series of approximately 15 similar notes. In a meticulous analysis of atypical Blackcap recordings on the online portal xeno-canto, we identified 12 cases of similar atypical singers distributed across Europe. We compared the vocal patterns of these atypical singers with the well-known Blackcap song variant leiern and concluded that there are important differences. People participating in common bird censuses should be aware of this variability in Eurasian Blackcap songs and the occurrence of atypical singers to avoid misidentification. The description and reporting of such observations will help improve knowledge of the complex subject of bird vocalisations.