Locally elevated cortisol in lymphoid organs of the developing zebra finch but not Japanese quail or chicken

•Glucocorticoids are important for production of functional lymphocytes.•Circulating corticosterone levels during development differ across 3 avian species.•Zebra finch lymphoid organs have very high cortisol and low corticosterone levels.•Quail and chicken lymphoid organs have low cortisol and low corticosterone levels.•Local glucocorticoid levels show species-specific patterns.

Glucocorticoids are important for production of functional lymphocytes and immunity. In altricial neonates, adrenal glands are unresponsive and local glucocorticoid synthesis in lymphoid organs may be necessary to support lymphocyte development. Precocial neonates, in contrast, have fully responsive adrenal glucocorticoid production, and lymphoid glucocorticoid synthesis may not be necessary. Here, we found that in altricial zebra finch hatchlings, lymphoid organs had dramatically elevated endogenous glucocorticoid (and precursor) levels compared to levels in circulating blood. Furthermore, while avian adrenals produce corticosterone, finch lymphoid organs had much higher levels of cortisol, an unexpected glucocorticoid in birds. In contrast, precocial Japanese quail and chicken offspring did not have locally elevated lymphoid glucocorticoid levels, nor did their lymphoid organs contain high proportions of cortisol. These results show that lymphoid glucocorticoids differ in identity, concentration, and possibly source, in hatchlings of three different bird species. Locally-regulated glucocorticoids might have species-specific roles in immune development.