Raptor populations on islands are limited by resource availability and the dispersal possibilities for young birds, which are often determined by the size of the island. This leads to differences in population dynamics and viability compared to mainland populations. Human land use modifications on islands such as agriculture, forestry, excessive hunting, and urban infrastructure development may affect resource availability and increase risks to these populations, ultimately threatening their survival. Consequently, many island raptor populations have been dramatically reduced or driven to extinction and have never fully recovered. The conditions necessary for their long-term persistence remain uncertain. Gotland, a large, human-dominated island located in the Baltic Sea, is home to one of the densest populations of Golden Eagles (Aquila chrysaetos) in the world. However, the drivers of population dynamics remain unknown, and many speculations exist that require empirical testing. Approximately 86 Golden Eagle territories were identified and surveyed across Gotland, an island spanning approximately 3,200 sq.km (152 km long, 52 km wide, with an 800 km coastline). We investigated the spatial drivers of breeding dynamics in this eagle population, evaluating the effects of territorial habitat composition, overlap with White-tailed Eagles, prey density, and neighborhood effects on territorial productivity. The average productivity was 0.41 fledglings per pair, which varied annually, with approximately 72% of territories occupied and 32% being successful. Despite significant variation in habitat composition across territories, spatial differences in productivity were primarily influenced by the proportion of coniferous forest (nesting habitat), access to coastal areas (greater prey diversity), the density of the main prey species (roe deer, Capreolus capreolus), and the reproductive status of neighboring territories in a year. Several novel findings emerged: the role of roe deer as a potential prey species had been previously underappreciated, proximity to the coast was associated with increased productivity, and the variation in spatio-temporal reproductive dynamics across neighboring territories appears to influence overall population dynamics. This relationship warrants further study. We discuss the implications of these findings for the long-term conservation and persistence of this iconic island population and similar populations worldwide.
