Friends or foes? Gyrfalcon – Golden Eagle interactions in the Scandinavian Mountains

Sammanfattning

Climate change, habitat loss and human persecution are threatening raptor populations globally, making science based conservation strategies essential to preserve healthy populations in the future. The importance of a multi-species or community approach in conservation is increasingly recognized, especially for species utilizing the same resources. However, in arctic and sub-arctic environments, extensive knowledge on factors affecting population dynamics of sympatric raptor species is limited. This exploratory study used over 20 years of monitoring data on gyrfalcons (Falco rusticolus) and golden eagles (Aquila chrysaetos) in the Swedish mountain region to analyse spatial and temporal trends of distribution and productivity of these two species in relation to environmental variables and interspecific presence. Two main questions were addressed; 1) How do fluctuations in prey populations, weather variables and topography of nesting sites affect the territorial occupancy and productivity of gyrfalcons and golden eagles? and 2) Do gyrfalcons and golden eagles affect each other’s territorial occupancy and productivity? Regression modeling and model selection based on Corrected Akaike Information Criterion (AICc) were used to identify key predictors. Results indicated that out of the environmental variables golden eagles seemed to be more affected by prey densities and gyrfalcons by spring weather conditions. A positive effect of interspecific presence was seen for golden eagle occupancy, while remaining tests of interspecific impact showed neutral effect. Limited or no significant effect in either direction for many of the models likely indicate that different factors act simultaneously and influence population dynamics in complex ways. Additionally, quality of the monitoring data varied across years, and results should be interpreted with caution. Future research should incorporate variables such as exposure of nesting sites and habitat characteristics of nesting territories, in addition to replication of the key analyses in this study to confirm the validity of the results. A more comprehensive monitoring of these species and ecosystem, and understanding built on it, will provide a stronger foundation to create targeted, multi-species conservation strategies in areas where climate and resource dynamics may change rapidly in the future.