Stable isotope ecology of an Arctic raptor guild

Abstract

As top predators in a rapidly changing environment, Arctic raptors serve as indicator species of ecosystem health. The degree to which populations exhibit dietary plasticity and partition resources on an interspecific basis under dynamic ecological conditions may be indicative of climate change resilience. It is therefore crucial to develop accurate and broadly applicable methods for characterizing the diets of wild populations. In this dissertation, I assessed the performance of Bayesian stable isotope mixing models (BSIMMs) as a method of characterizing diet in free-living raptor populations, developed novel methods to refine their accuracy and applicability, and applied an isotopic approach to address broad trophic hypotheses within an Arctic raptor guild. First, I evaluated the use of BSIMMs in a population of Gyrfalcons (Falco rusticolus) by comparing modelled diet estimates to high-accuracy nest camera diet data. I found that the isotopic method effectively characterized diet at the population level and accurately identified temporal shifts in Gyrfalcon diet on a seasonal and interannual basis. Second, I developed a novel method for the estimation of trophic discrimination factors (TDFs) in wild populations and tested it in three published datasets. The new method outperformed other methods of TDF estimation in all cases, ultimately increasing the accuracy and applicability of the BSIMM approach under certain circumstances. Third, I applied an isotopic approach to characterize interspecific niche overlap and individual specialization in an Arctic raptor guild (Gyrfalcons, Golden Eagles [Aquila chrysaetos], and Rough-legged Hawks [Buteo lagopus]) under varying degrees of resource abundance. I found the three species overlap in their isotopic niche, but that overlap was reduced when more prey types were available (i.e., an influx of cyclic arvicoline rodents). In Gyrfalcons, the level of individual specialization increased with increasing population niche width in accordance with the niche variation hypothesis.