Spatial, seasonal and individual variation in the diet of White‐tailed Eagles Haliaeetus albicilla assessed using stable isotope ratios

Abstract

Many raptor species are considered to be generalists, taking a range of prey species. However, longitudinal dietary records are often scarce, although necessary for characterizing niche width of species at population and individual levels. Quantifying raptor diets at large spatio-temporal scales is often necessary for refining conservation efforts, although it can be particularly difficult and may involve a great effort by conventional means. Therefore, we adopted the analysis of stable isotopes in tissues of predators and their potential food sources as a complementary methodology for assessing animals' diet. We examined the isotopic composition (d 13 C and d 15 N) of White-tailed Eagles Haliaeetus albicilla from Germany, Finland and Greenland to detect patterns of dietary variation and quantify diet composition. The isotopic analysis included liver and muscle samples from Eagles of the three populations together with 16 potential food sources in the German population. Our results suggested dietary differences between German and Greenlandic Eagles, in accordance with the availability of freshwater and marine habitats in each population. Within the German population, we found seasonal shifts in isotopic ratios, suggesting the birds responded to temporal changes in food availabilities, and agerelated isotopic differences, indicating different diets in adults and juveniles. Isotopic values of liver and muscle tissues collected from the same animal showed intra-individual short-term changes in the German and Finnish but not Greenlandic population. This suggests that local feeding niches of this generalist predator may vary with local food supplies, which determines the niche width (from generalist to specialist) at the individual level. Our results also revealed that game mammal carcasses constitute an important food source (29.5% of diet) for the German Eagle population during the winter half-year corresponding to the hunting season. This result is of relevance to management and conservation because the White-tailed Eagle and other raptor species are affected by the ingestion of lead ammunition from shot mammalian carcasses.

Density‐dependent effects on reproductive performance in a recovering population of White‐tailed Eagles Haliaeetus albicilla

“…, Nadjafzadeh et al . ). Our analyses suggested that the reproductive performance of individual breeding pairs decreased with reduced availability of water bodies in their vicinity.…”

“…Stable isotope analyses showed that in north‐east Germany, aquatic organisms contribute 73% to the diet of the White‐tailed Eagle in winter and 91% in summer (Nadjafzadeh et al . ). Therefore, in our study population aquatic organisms constitute the primary food resource of the species during the breeding season.…”

“…, , Nadjafzadeh et al . ). Moreover, for each radius we calculated the proportion of surface area covered by inland waters and coastal lagoons based on the Corine Land Cover 2006 dataset.…”

“…Large parts of its diet are hunted on the water surface (50%), but also on open ground (20%), in sparsely vegetated areas (20%) and in flight (10%, Wilman et al 2014). Stable isotope analyses showed that in north-east Germany, aquatic organisms contribute 73% to the diet of the White-tailed Eagle in winter and 91% in summer (Nadjafzadeh et al 2016). Therefore, in our study population aquatic organisms constitute the primary food resource of the species during the breeding season.…”

Spatial and temporal patterns in age structure of Golden Eagles wintering in eastern North America

“…Key words: age cohorts, Aquila chrysaetos, camera trap, latitudinal variation, wintering behavior Over the course of a full annual cycle, animals may change their foraging behavior (Dearing 1997), diet (Nadjafzadeh et al 2016), movement strategies (Newton 2007), space use (Sumasgunter et al 2016), energy budget (Czenze et al 2017), gonad size and sexual behavior (Gill 2006), and brain size, cranial morphology, and metabolic rate (L azaro et al 2017). This variation is often driven by seasonal fluctuations in either resource availability or reproductive physiology.…”