As migratory species move across their annual ranges, they may face challenges that can ultimately influence population dynamics. Audouin’s Gull (Ichthyaetus audouinii) is a long-lived migratory species that breeds in colonies across the Mediterranean, with Catalonia hosting most of the breeding population. Threats and population dynamics are well documented at breeding colonies, but less is known about spatial distribution outside colonies. By combining long-term mark-recapture data with citizen-science observations, we assessed the spatial distribution of marked individuals in Catalonia, Valencia and the Balearic Islands using kernel utilisation distributions, overlap indices, PERMANOVA and dispersion tests. We detected significant differences in distribution between breeding and non-breeding periods, age classes and natal colony groups. Natal colony group explained the highest proportion of variation, followed by breeding period and age class. Breeding and non-breeding distributions overlapped strongly at broad scales but differed in core-use areas. Younger age classes showed broader distributions than adults, suggesting age-dependent changes in space use. These results provide important insights into the diverse drivers shaping Audouin’s Gull spatial distribution and highlight the potential of citizen science to provide valuable information on species distribution beyond breeding colonies and across life stages, a crucial step for guiding effective conservation measures.
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