DOI: 10.20350/digitalcsic/16231
title: Reduced trophic niche breath is associated with higher productivity in a recovering apex predator population [Dataset]

description: [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 (&lt; 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 (&lt; 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).
description: [Methods for processing the data] For prey quantification at a site and sampling episode (one visit per pair and year) we estimated minimum number of prey individuals of each species. Data was tabulated in excel format comprising 1,916 records and 14 fields (columns), including information on pair identification, year of sampling, prey species and number, reproductive data for each monitored event and seven variables related with territory traits that have been found to have an influence on golden eagle’s productivity for the studied population (Fernández-Gil et al. 2023).
description: Understanding trophic and demographic dynamics of apex predators is of paramount importance for ecosystems conservation. Apex predators are usually free from predation and, thus, main drivers of population dynamics are trophic resources availability affecting breeding performance. Albeit food habits have been described in many apex species, the effects of changes in the trophic niche on long-term demographic dynamics are poorly known. We describe the long- term (N = 25 years) changes in trophic niche breath of a recovering golden eagle population in a Mediterranean landscape (North Spain), and searched for potential correlates with their productivity (i.e., number of fledged eaglets per controlled pair) as a proxy of their breeding performance (N = 290 pairs*years). We identified a total of 3,475 prey items from 77 species; rabbits, hares and red-legged partridges were the most frequent prey consumed (overall 51%), followed by roe deer (10%), red-billed chough, red foxes and woodpigeons, all of them with &gt;5%. Prey diversity in eagle’s diet decreased along the study period. Rabbits and roe deer consumption increased, hares and partridges decreased, while foxes, choughs and woodpigeons showed no significant trends. Prey diversity and red-legged partridge consumption were negatively correlated with productivity at territory level, while rabbits, corvids and pigeons showed strong positive relationship with productivity. The size of the territory showed the strongest positive relation with productivity, while roughness was negatively correlated. Rabbits and ungulates showed negative and positive correlation with roughness, respectively, while predators consumption has a negative relation with the size of the territory. Our findings give insights the potential trophic mechanisms driving the dynamics of recovering apex predator populations; a reduction in the trophic niche breath towards specific groups of prey, which could be due to a higher availability and individual specificity towards these prey species, might enhance productivity at territory level and, ultimately, influence population dynamics facilitating the recovery process. The remarkable increasing consumption of wild ungulates and predators, and even of other apex consumers, suggest that the current population recovery and reduced trophic niche breath may facilitate this eagle population to exhibit its apex role and contribute to ecosystem functionality.