Abstract

Urban development presents both challenges and opportunities for wildlife, with some species adapting successfully while others decline. The Caspian Gull Larus cachinnans, once largely restricted to natural habitats, has increasingly colonised urban environments in Poland. Between 2018 and 2024, the number of breeding pairs rose from just two to approximately 464, with most nesting on rooftops, often alongside Herring Gulls Larus argentatus. Caspian Gulls are now beginning to outnumber Herring Gulls in many colonies. Ringing data indicate that the majority of urban-breeding Caspian Gulls originate from natural colonies, with individuals dispersing from sites in Poland, Germany, Belarus and Slovakia. Rooftop colonies appear to offer favourable conditions, including reduced predation risk and increased nesting opportunities. The rapid expansion of Caspian Gulls into urban areas, and their likely competitive interactions with Herring Gulls, may lead to hybridisation and broader ecological and demographic shifts in urban bird communities. Continued monitoring is essential to assess the long-term impacts on urban biodiversity and interspecific dynamics.