Feather and claw hydrogen isotope values
The feather hydrogen isotope (δ2Hf) values were significantly higher and predicted latitudes were significantly lower in resident than in migrant juncos (Fig. 2 a, b, e, f; S1, S2; Table S1). The two populations exhibited non-intersecting ranges of δ2Hf values, suggesting distinct, non-overlapping breeding latitudes (migrants δ2Hf range = -121.07 – -98.8 ‰; residents δ2Hf range = -60.0 – -42.9 ‰; Fig. S1, S2). The claw hydrogen isotope (δ2Hc) values did not differ between migrants and residents, suggesting that they overwintered at the same latitude (Fig. 2c, d, g, h; S1, S2; Table S1). Difference in the latitude of breeding and development of immature juncos provide a strong rationale to investigate the difference in the neuroendocrine response between resident and migrant junco populations.