The effects of neonatal handling on adrenocortical responsiveness, morphological development and corticosterone binding globulin in nestling American kestrels (Falco sparverius)

Early developmental experiences play an important role in development of the adult phenotype. We investigated the effects of neonatal handling on the hypothalamic–pituitary–adrenal axis in a free-living avian species, the American kestrel (Falco sparverius). In the handled group (H), kestrel chicks were handled for 15 min/day from hatching until 26 days of age, after which time blood samples were collected for analysis of adrenal responsiveness and corticosterone binding globulin (CBG) levels. The non-handled control group (NH) was left undisturbed until 26 days of age when blood samples were collected and analyzed as above. Handled and NH kestrels did not differ in body condition index. Both total corticosterone (CORT) and CBG capacity were dampened significantly in H kestrels. However, free CORT did not differ between the two groups. In addition, hormone challenges of corticotropin releasing factor and adrenocorticotropin hormone were compared to saline injections to determine if the pituitary or the adrenal glands, respectively, were rendered more or less sensitive by handling. There was no difference in the responsiveness of H and NH kestrels to either hormone challenge. It is clear from these data that handling had an affect on fledgling phenotypic development, although whether the effects are permanent or ephemeral is unknown.

► Daily investigator handling (15 min/day) dampens adrenoresponsiveness in nestlings.
► CBG levels are also reduced in handled nestlings.
► Consequently, free corticosterone levels are similar in handled and unhandled young.
► Responses to ACTH and CRF challenges are similar in handled and unhandled nestlings.