Studying gulls: What can we learn from these opportunistic, flexible, and explorative species?

Gulls are a taxonomic group of birds known for their flexible, opportunistic behaviour, their use of a wide range of habitats, and their strong response to human activities. Since 2008, we have GPS-tracked more than 800 individuals of seven gull species in Europe and three in the Americas. We have addressed a variety of biological and ecological questions as well as several applied topics on conservation and human pressures. In this seminar talk I will focus on two species and topics. 1) How tracking helps us to understand behavioural plasticity: We studied the distribution, foraging behaviour, and habitat choices of Common Gulls (Larus canus) in nine breeding colonies in northern Germany, including sites in the North Sea, the Baltic Sea, as well as inland. Common Gulls use a mosaic of habitat patches, depending on their availability and suitability. As opportunistic species, they demonstrate wide phenotypic plasticity across different anthropogenic landscapes. 2) How tracking helps us to understand migratory connectivity and species' ecology: It has only recently become possible to tag small gull species with high-resolution tags. This allowed us to tag Little Gulls (Hydrocoloeus minutus), a scarce and poorly understood species of high conservation concern, at the western edge of their distribution in the eastern Baltic Sea. The birds from this small breeding colony spread out during migration and winter across half of Europe. Their main wintering areas are located in the Mediterranean Sea and the eastern North Atlantic. Little Gulls were almost exclusively marine throughout their entire migration cycle, using habitats ranging from estuaries to the deep sea. These two examples illustrate the strong potential of GPS tracking to understand the migration and habitat choices of gulls.