Meeting Abstract

P1.28  Friday, Jan. 4  Assessing the isotopic niche of passerine birds: analysis of the carbon and nitrogen isotopic composition of tissues and diet. RAMIREZ-OTAROLA, N*; SABAT, P; BOZINOVIC, F; MARTINEZ DEL RIO, C; Univ. de Chile, Santiago; Univ. de Chile, Santiago; Pont. Univ. Cat. de Chile, Santiago; Univ. of Wyoming, Laramie nat.rotarola@gmail.com

We analyzed the carbon and nitrogen isotopic value of the muscle, liver, and crop contents (“diet”) of 132 individuals of 16 species of Chilean birds. The nitrogen content of diet was tightly correlated with the fraction of gut contents represented by insects relative to plant material. The carbon and nitrogen isotopic values of diet, liver, and muscle were all linearly correlated, implying high temporal consistency in the isotopic value of the diet of these birds. However, δ¹⁵N was not significantly related with the percentage of insects in diet. These results cast doubt on the applicability of the use of ¹⁵ N enrichment to diagnose trophic level in, at least some, terrestrial ecosystems. However, the residuals of the relationship relating the isotopic value of bird tissues with those of their diet were weakly negatively correlated with insect intake. We hypothesize that this negative correlation stems from the higher quality of protein found in insects relative to that of plant materials. Finally, our data corroborated a perplexing and controversial negative relationship between tissue to diet isotopic discrimination and the isotopic value of diet. We suggest that this relationship is an example of the commonly observed regression to the mean effect that plagues many scientific studies.