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Combining stable isotope analysis and conventional techniques to improve knowledge of the diet of the European Roller Coracias garrulus

Catry, Inês, Sampaio, Ana, Silva, Mónica C., Moreira, Francisco, Franco, Aldina M. A., Catry, Teresa
TheIbis 2019 v.161 no.2 pp. 272-285
Coleoptera, Coracias garrulus, Tettigoniidae, adults, birds, blood, cameras, carbon, diet study techniques, evolution, females, food choices, foraging, grasshoppers, habitat conservation, intraspecific variation, males, nestlings, niches, nitrogen, nutrition information, pellets, prey species, stable isotopes, video recording, Europe
Diet studies are crucial for understanding the ecology and evolution of species, as well as for establishing appropriate conservation and management strategies. However, they remain methodologically challenging due to variation between seasons, sites, sexes or age groups and even variation between individuals. Due to method‐specific characteristics and biases, a combination of existing techniques can overcome the inherent limitations of each technique and provide a more accurate and broad picture of species’ food preferences. Here, we examine diet information obtained using three different assessment methods to better understand the trophic ecology of the European Roller Coracias garrulus, a species targeted by conservation measures in Europe. First, we analysed regurgitated pellets and video‐recordings to report the diet composition of adult and nestling Rollers, respectively. Secondly, we used stable isotope analysis (SIA) to investigate adult sexual diet segregation as well as to confirm the main findings regarding adult and nestling diets obtained through conventional methods. Based on the analysis of pellets, the diet of adult Rollers was dominated by Coleoptera, whereas camera images revealed that the diet of nestlings was dominated by Orthoptera, mainly grasshoppers and bush crickets. Blood isotopic signatures of adult and nestling Rollers confirmed the results obtained through pellet and video‐recording techniques. Of the three methods, pellet analysis provided the most comprehensive trophic information regarding the detectable prey spectrum and prey species contribution, as well as basic diet information for the SIA. Our results also highlight the potential of SIA for assessing intraspecific variation in diet by sampling individuals of known age and sex, which is often unfeasible through conventional approaches. SIA analysis showed no differences in δ¹³C and δ¹⁵N ratios of blood between males and females and a high degree of overlap amongst isotopic niches, suggesting no sex‐specific partitioning in resource use. Overall, we showed that the combination of different methods could be used to gain new and clearer insights into avian trophic ecology that are essential for informing habitat management aiming to improve availability of foraging resources.