A new study shows that two neighbouring populations of Finnish white-tailed eagles—one around the Baltic Sea coast and one in inland Arctic Lapland—are recovering at similar rates, but with some important differences in how various age groups contribute to that recovery. The findings support future monitoring and management of large raptors and offer insights for protecting other long-lived species.
The white-tailed eagle (Haliaeetus albicilla) was once a rare species in Europe due to persecution and pollution. Thanks to legal protection and cleaner environments, many populations have been increasing.
In a recent study published in the journal Oikos, researchers from the Universities of Turku and Helsinki in Finland, and the Swiss Ornithological Institute analysed more than 50 years of data from the Finnish Baltic Sea and Lapland, including breeding pair counts and chick numbers of 2,468 nests of almost 1,000 territories, and ringing, resightings, dead recoveries, and genetic identification of 7,179 individuals.
The combination of all this data in one Integrated Population Model show that both populations experienced similar growth rates of around 9 percent per year, supported by high adult survival typical of long-lived birds of prey. However, the demographic balance differed.
“Both populations are clear conservation success stories in Finland, but they did not recover in exactly the same way,” explains the lead author of the study, Academy Research Fellow Carina Nebel from the University of Turku. “In the Baltic Sea, many younger birds survive well but face increasing competition for breeding sites. In Lapland, adult eagles do particularly well, while survival of younger birds is lower.”
Such differences matter because they show that similar trends in numbers can arise from different demographic structures. To understand how species are responding to change, the study shows that it is necessary to look beyond simple counts and focus on which life stages are more important for growth.
“White-tailed eagles are a flagship species in northern Europe, and their recovery demonstrates the value of long-term protection,” adds Professor Toni Laaksonen from the University of Turku. “This study also shows the importance of collecting long-term field data, ringing and resighting, and combining it with state-of-the-art statistical tools, which gives us a much clearer picture of how large, long-lived species recover—knowledge that is essential for effective conservation.”
For the white-tailed eagle in particular, the long-term dataset was collected by volunteers of the White-tailed Eagle Working group working first under WWF Finland and nowadays under the Osprey foundation. Their sustained efforts over many decades made this study possible and have been crucial for the conservation of the species.
By showing how similar recoveries can be achieved in different ways, the study provides a useful basis for future monitoring and management of large raptor species in Finland, but also elsewhere. It also shows how long-term volunteer monitoring, combined with modern scientific methods, can help guide the protection of other long-lived species in a changing world.