Many Herring Gulls nesting at Texel (Wadden Sea) forage for mussels at any of149 breakwaters along the mainland coast south of the colony. Arguably, thearea is one of the prime feeding habitats for one of the largest colonies withinThe Netherlands. As a precautionary measure to be prepared for sea level riseas a result of global warming, the coastline need be strengthened and anoperation is now due in which a significant part of this hard substrate will becovered in sand. Sightings of colour-ringed individuals, collected since 1986,show that many individuals are in fact very site faithful and a part of thesebirds will lose their favoured breakwater(s) and will have to look out for alternativeopportunities. An intensified colour-ring programme has been launchedto obtain more information on individual site fidelity in this major feedingground, so that the effect of this ‘natural experiment’ can be evaluated withmore precision. Observers are encouraged to collect more sightings data in thearea and a list of ‘sites’ is provided to ensure the location of their observationscan be pinpointed with the accuracy of individual breakwaters (Appendix 1).