Early developmental experiences play an important role in the adult phenotype. My study was designed to investigate the effects of neonatal handling on the hypothalamic-pituitary-adrenal (HPA) axis in two wild-caught avian species, the American kestrel (Falco sparverius) and the European starling (Sturnus vulgaris). For the kestrel manipulations chicks in the experimental group (H) were handled from hatching until 26 days of age, after which time blood samples were collected for analysis of corticosterone (CORT) and corticosterone binding globulin (CBG). The control group (NH) was left undisturbed until 26 days of age and then were analyzed the same as H kestrels. Handled and NH kestrels did not differ in the metric of condition measured body condition index (BCI). Both total CORT and CBG capacity were dampened in H kestrels, although free CORT did not differ between the two groups. In addition, hormone challenges of corticotropin releasing factor (CRF) and adrenocorticotropin hormone (ACTH) were utilized and compared to saline injections to determine if the pituitary or the adrenal glands, respectively, were more or less sensitive due to handling. There was no difference between the H and NH kestrels, regardless of hormone challenge. It is clear from these data that handling had an affect on fledgling phenotype, however, at which level(s) of control alteration occurred remains unclear. Additional and longer-term studies are needed to better understand all of the effects of neonatal handling and the short- and long-term costs and/or benefits to fitness in the American kestrel.
Body condition, adrenocortical responsiveness and corticosterone binding globulin (CBG) were used as determinants of the effects of neonatal handling in starlings. After I 7 days of neonatal handling, starlings showed no dampening of adrenoresponsiveness characteristic of other avian and mammalian species. Additionally, body condition did not differ between handled (H) and non-handled (NH) starlings, nor did CBG capacity. Subsequently, there was no difference in free CURT titers between H and NH nestlings. Several factors may have contributed to the results of this study being in contrast to those of my kestrel study: sample size was lower, the most critical period of influence may have been missed, and/or starlings, being highly adaptable to adverse conditions, may be particularly resistant to the effects of small but regular perturbations such as daily handling.