<p>The stable hydrogen isotope (δ²H) composition of feathers is commonly used to infer the geographic origin of birds. The comparison of δ²H data from multiple tissues can provide additional resolution on movement patterns as different tissues integrate isotopic signatures over varying time scales, but such inferences require consideration of tissue-specific isotopic discrimination that is largely controlled by physiological processes. In this study, we experimentally estimated δ²H tissue-specific discrimination between feathers and red blood cells (Δ²H_{feather−RBC}) in two passerine species, <i>Zonotrichia capensis</i> and <i>Diuca diuca</i>, maintained under controlled dietary and water conditions. These two tissues can be easily collected from wild-caught birds, making them practical for field-based isotopic studies. Feathers collected from both species had consistently higher δ²H values by ~ 25‰ relative to red blood cells. These offsets closely matched mean (± SD) Δ²H_{feather−RBC} of wild-caught <i>Cinclodes nigrofumosus</i> (+ 24 ± 3‰), a sedentary coastal passerine in central Chile. Our results emphasize the importance of accounting for tissue-specific isotopic discrimination when interpreting patterns in δ²H values among tissues that can identify bird movements not possible with a single tissue approach. Our findings also demonstrate that experimentally derived tissue-specific discrimination factors can be effectively applied to wild passerine populations, supporting their use in improving the accuracy of isotope-based movement studies.</p>