When the gulls come to town

Throughout Europe, many natural breeding colonies of ground-nesting Larus-gulls strongly decreased in numbers or even became deserted during the past decades. The opportunistic gulls often moved to industrialized and urbanized sites where they frequently come into conflict with humans. The strong increase in urban gull populations is thought to be linked to the presence of predator-free nesting sites (notably roof-tops) in combination with a high availability of food in the form of food wastes or takeaways discarded by tourists. In coastal communities the general perception prevails that the roof-nesting gulls become increasingly aggressive and survive by snatching food from unsuspecting tourists. There are, however, very few studies that show where urban gulls are collecting their food and whether or not this behavior can sustain the urban populations. Therefore we mounted UvA-BiTS gps-trackers on 75 Lesser Black-backed Gulls and 26 Herring Gulls breeding at the Belgian and Dutch coast. Here we report on the foraging behavior of these gull and specifically focus on the use of urban environments. Our study shows that although both gull species are considered to be true generalists, individuals within the population often show extreme specialism with respect to both foraging behavior and habitat use. Only a minority of the roof-nesting gulls actually did use the urban environment for foraging and not all gulls specialized in food snatching actually nest in the urban environment. This has important implications for the management of gull nuisance which in Belgium currently targets the entire roof-nesting population.