Reduced trophic niche breath is associated with higher productivity in a recovering apex predator population [Dataset]

[Description of methods used for collection/generation of data] The dataset includes the raw data used to study the golden eagles´ diet in Burgos province. It includes data on prey remains collected below nests and at nearby plucking posts (mostly fresh remains, and some from pellets), although some prey remains (< 1%) were identified by direct observation of hunting eagles. Prey items were identified de visu , either directly, or by comparing the remains with a reference collection of feathers (i.e., for bird species) or with a reference collection of skull, bones and skin (i.e., for mammals). Some prey remains were not identified at the specific level, and were tabulated at Order level (e.g., Lagomorpha), at Phylum level (Reptilia), or even at a more general level (e.g., small mammals, including Rodentia and Insectivora). Prey remains were collected below nests and at nearby plucking posts (mostly fresh remains, and some from pellets), although we also accounted with some prey remains (< 1%) identified by direct observation of hunting eagles. Our study period spanned 25 years, from 1992 to 2017; during this period, we sampled annually an average of 11.6 eagle territories/pairs (n= 290 pair*years), distributed over the entire study area (i.e. 70 different territories sampled along the study period).  Prey items were identified de visu, following a similar procedure as Whitfield et al. (2009), either directly, or by comparing the remains with a reference collection of feathers (i.e., for bird species) or with a reference collection of skull, bones and skin (i.e., for mammals), using also two complementary field guides for prey identification (Brown et al. 1987, García 2013).