Fig. 3.

a δ¹⁵N vs. δ¹³C isotopic composition of feathers from Darwin’s finches, specifically the vampire finch (G. septentrionalis from Wolf Island; red triangles), medium ground finch (G. fortis; San Cristóbal Island; green squares), and small ground finch (G. fuliginosa; San Cristóbal Island; green circles), in comparison to other animal tissues (grey dots). For the finches, each symbol represents values recovered from one individual bird. Error bars, where present, indicate the range of values obtained from two to three different feathers from the same individual. δ¹³C for ground finch feathers ranged from − 24.1 to − 18.7‰ vs. PDB, and from − 23.8 to − 16.1‰ vs. PDB for vampire finches. δ¹⁵N ranges from + 4.9 to + 11.7‰ for ground finches and between + 14.2 and + 25.1 ‰ δ¹⁵N for vampire finches. The vampire finch feathers differ significantly in δ¹⁵N (ANOVA p < 0.0001), but not δ¹³C (ANOVA p > 0.9). Isotopic values from other animals were reported in the following: [44–46, 78–87]. b Non-metric multidimensional scaling (NMDS) ordination of three species of gut microbial communities of Darwin’s finches according to diet. Taxonomic (OTU) clustering is at 97% identity and abundance weighted by taking the fourth-root of the OTU relative abundance in each finch