HUIG, N, R-J. BUIJS & E. KLEYHEEG (2016) Foraging Herring Gulls Larus argentatus on the Dutch coast: city slickers or true sea gulls?. LIMOSA 89 (2): 58-66.

Increasing numbers of Herring Gulls use the coastal city of The Hague in the Netherlands as a foraging site, and people claim that this seagull has become an urban gull. However, numbers of Herring Gulls in natural habitat (beaches) in the Netherlands are known to peak in (late) summer. We studied whether gulls foraging in the city would also visit the beach, and whether a seasonal pattern in habitat preference of urban gulls can explain the peak in gull numbers on the beach in late summer. Systematic surveys of Herring Gulls colour-ringed in a nearby breeding colony in the Port of Rotterdam revealed that around 25% of adult Herring Gulls used both habitats, while over 50% were seen only on the beach. The city was visited mostly by adult male Herring Gulls in early summer, after which most individuals moved to the beach. The number of immature Herring Gulls was much higher on the beach than in the city and remained fairly stable throughout the summer. Similarly, juvenile birds arriving from the colony also appeared mostly on the beach. These observations suggest that adult Herring Gulls mainly visit the city in early summer when the demand for (anthropogenic) food for chicks is high. Females may choose to forage on the beach earlier in the season due to strong competition with male Herring Gulls and Lesser Blackbacked Gulls Larus fuscus in the city. After fledging of the chicks, anthropogenic food sources in The Hague are largely abandoned and Herring Gulls of all ages forage together on the beach. We thus conclude that abundant presence of Herring Gulls in the city is seasonal and that the individuals involved are at least part of the year still typical seagulls rather than urban gulls.

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