The surrogacy potential of white-tailed sea eagle nesting habitat on islands of the Baltic Sea

In order to tackle the current biodiversity crisis, a plethora of tempting shortcuts, such as the surrogate species approach, have recently been used to pinpoint important areas for protection. At the same time, species-specific conservation programmes are implemented in order to ameliorate the status of target threatened species. In the cases where species-specific programmes are evaluated and found to provide no apparent benefit to the target species, it is important to evaluate whether such conservation efforts may benefit other taxa sharing the same landscape with the target species. Here we assess the surrogacy potential of white-tailed sea eagle (WTSE) nesting habitat as indicator of biodiversity richness (using vascular plants and fungi as surrogated taxa) on islands of the Archipelago Sea in South-western Finland. We compared species richness on islands with and without a WTSE nest. We found weak evidence that islands with a WTSE nest support higher richness of vascular plants than islands without a nest. Conversely, we found no evidence that WTSE nests could be valid surrogates for fungi species inhabiting old-growth forests. Within the spatio-temporal and ecological limits of the present study, we suggest that the nesting habitat of WTSE may hold some surrogate potential for taxa, such as vascular plants, that may indicate high habitat diversity. This finding however remains to be confirmed. At the same time, it appears evident that the WTSE nesting habitat has poor surrogate potential with regards to old-growth forests. Overall, our findings line up with a growing body of other studies calling for caution and careful evaluation of the surrogacy efficiency of single species.