Phenotypic characteristics and moult commencement in breeding Dutch Herring Gulls Larus argentatus & Lesser Black-Backed Gulls L. fuscus

We describe ten phenotypic characteristics and moult commencement in an inland colony of Herring Gulls Larus argentatus and Lesser Black-backed Gulls L. fuscus in The Netherlands. All features were checked for difference between sexes and, when possible, known-aged birds were described. Both taxa exhibited wide variation in single characteristics, most apparent in the range of upperpart grey tone, iris speckling and the pattern on P10 and P9. Herring and Lesser Black-backed Gulls in this colony showed considerable overlap with birds from Scandinavia and from Britain, which justifies the name ‘Dutch intergrade’, sometimes used for breeding Lesser Black-backed Gulls in The Netherlands.