Models to examine the potential sources of variation in the isotopic ratios of nitrogen (δ¹⁵N) in red blood cells (δ¹⁵N_RBC), serum proteins (δ¹⁵N_Proteins), and serum amino acids (δ¹⁵N_AAs) as well as the differences between δ¹⁵N_RBC and δ¹⁵N_Proteins (Δ_RBC-proteins) and δ¹⁵N_RBC and δ¹⁵N_AAs (Δ_RBC-AAs) in adult (≥3 y) female caribou in Denali National Park and Preserve, Alaska, March, 1993–2007.

a<p>Winter locations were acquired 20 Jan–11 Feb, 1–2 months prior to blood sampling.</p>b<p>Late winter locations were acquired 8–25 Mar at blood sampling.