Can apex predators at the periphery of their range be effectively safeguarded? The Greater Spotted Eagle Clanga clanga in Poland

This study assessed the status of the Greater Spotted Eagle (Clanga clanga), one of Europe's most endangered vertebrates and globally one of the least numerous raptor species. It was conducted over 28 years in Central Europe's largest lowland marsh and peatbog complexes, where diverse protection measures were implemented in the most recent 20 years, including restricted-access zones, watercourse regulation, and artificial nesting platforms. The mean breeding pair density over the past 28 years was 0.5/100 km² pairs, with an average of 0.27/100 km² pairs initiating broods. Furthermore, 81.5 % of initiated broods succeeded, yielding 0.20 fledglings/100 km² yearly. European Pine Martens (Martes martes) were a primary cause of nest failures. On average, hybridization between Greater Spotted Eagle and Lesser Spotted Eagle (Clanga pomarina) was observed within 35.8 % of pairs. The Biebrza Marshes turned out to be a suboptimal breeding habitat, reflected in high hybridization rates, low breeding densities, and limited successful nesting pairs. Enhanced conservation efforts are crucial to maintain the species in its range in the Biebrza Marshes. The strategies to enhance the population status include improving habitat quality by reducing drainage, increasing the number of individuals in the population by preventing cainism through the rearing and reintroduction of younger nestlings in a brood, which are always killed by older siblings, and finally by reducing European Pine Marten populations to minimize predation.