Diet and breeding performance show variations across species' range and between different habitats. In the present paper, we report data on the diet and breeding performance of Golden Eagles Aquila chrysaetos monitored during a ten-year period in two semi-natural landscapes located at the eastern and western extremities of the Pyrenees mountain range. In the Mediterranean area of the Corbieres, the diet was dominated by the Rabbit Oryctolagus cuniculus (31.5% of the prey items). In the Atlantic area of the Basque Country, the diet was more diverse, with the highest proportion of intra-guild predation and the highest diet breadth ever recorded for the species (Levins index of diet breadth: 12.14 vs 6.81 in the Corbieres). The proportion of successful breeding attempts was significantly higher in the Corbieres (60%) than in the Basque Country (38.5%). The same was true for mean productivity, with 0.70 and 0.45 fledglings per territory and year, respectively. These differences were partly related to the excess of snow cover in April in the Basque Country. Our results provide an example of intra-population variability in a long-lived apex predator at the extremes of a geographical gradient involving climate and prey availability.
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Vol. 64 • No. 2