Stable isotope ratios in alpine rock ptarmigan and black grouse sampled along a precipitation gradient

• Published in: Basic and Applied Ecology
• Main Authors: Dehnhard, Nina, Yohannes, Elizabeth, Jenny, Hannes, Segelbacher, Gernot
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: ddc:570; Lagopus muta; rock ptarmigan
• Online Access: http://nbn-resolving.de/urn:nbn:de:bsz:352-0-348936; https://doi.org/10.1016/j.baae.2016.04.007

Rock ptarmigan (Lagopus muta) and black grouse (Tetrao tetrix) are two closely related alpine bird species that form relict populations in the European Alps. Besides manifold anthropogenic influences in this region, global climate change is forecast to lead to significant changes in temperatures and precipitation. We here analysed stable isotope ratios (δ 13 C and δ 15 N) of feathers of both bird species and their potential dietary plants across a longitudinal precipitation gradient in south-east Switzerland. Plant δ 13 C was higher at higher altitudes and in drier areas (coinciding with higher longitudes) while plant δ 15 N did not differ geographically. Black grouse δ 13 C reflected the longitudinal pattern in precipitation and plant δ 13 C, and there was no indication for a change in dietary composition with precipitation (i.e. no significant changes in δ 15 N). In contrast, rock ptarmigan δ 13 C was independent of precipitation and plant δ 13 C values and showed a significant increase in δ 15 N towards drier areas, suggesting a potential dietary shift. In rock ptarmigan, we furthermore investigated intraspecific differences with age, between males and females and among years, and did not find any biologically meaningful intraspecific differences. Interspecifically, rock ptarmigan feathers had significantly higher δ 13 C and lower δ 15 N values than black grouse, reflecting a dietary segregation between both species. This may partly be due to the higher altitudinal distribution of rock ptarmigan in combination with an altitudinal gradient in plant δ 13 C. In addition, however, species also segregated in δ 15 N, most likely caused by a higher proportion of invertebrate diet in black grouse. published published