Biological validation of fecal glucocorticoid and triiodothyronine measures in free-ranging Golden-headed Lion Tamarins (Kühl, 1820), (Mammalia: Primates: Callitrichidae: ): effects of the stress of capture and body condition

Glucocorticoids (GCs) and thyroid hormones (THs), along with other physiological mediators, modulate the responses that allow lifelong adaptation to predictable and unpredictable environmental challenges. This has sparked the interest of primatologists who, with the advent of non-invasive sampling techniques, have been able to investigate changes in GCs and, more recently, THs under field conditions. These techniques need a validation process to ensure that the measurements are biologically meaningful for the species and the matrix being studied. Here, we aimed to validate the measurement of GC and triiodothyronine (T3) metabolites (fGCs and fT3, respectively) in the feces of wild Golden-headed Lion Tamarins (GHLTs; Leontopithecus chrysomelas), inhabiting highly disturbed forest patches in southern Bahia, Brazil. We assessed the effects of capture, body condition (weight and score), sex, dominance status, and group identity on the levels of fGCs and fT3 in samples collected during capture events and regular group-monitoring days. We found that capture and handling had a significant impact on both fGCs and fT3, whereas body condition score was relevant only to the variation in fT3 levels. These findings confirm the notion that the procedure of capture is a suitable acute stressor to validate non-invasive hormone measures and that fT3 is a promising marker for studying the fluctuations in energetic condition. Overall, our results demonstrate that a simple biological approach is sufficient to verify the applicability of non-invasive GC and TH determinations in fecal samples of wild GHLTs.