1. The glucocorticoid axis is essential for coping with predictable and unpredictable

environmental variation. Despite this vital function, attempts to link individual variation

in the glucocorticoid axis to survival have yielded mixed results, which may be

due to endocrine variation caused by uncontrolled variation in environment and

life-history traits such as reproductive effort. We therefore studied the link between

the glucocorticoid axis and long-term survival using captive non-breeding

zebra finches.

2. We quantified the relationship between survival over a three-year period and

plasma corticosterone concentrations: (1) baseline, (2) stress-induced, (3) after induction

of negative feedback via dexamethasone injection and (4) after maximal

adrenal stimulation via adrenocorticotropin hormone injection.

3. Only stress-induced corticosterone predicted survival, with higher concentrations

being associated with lower survival. However, this effect differed significantly between

the sexes, being present only in males.

4. Stress-induced corticosterone concentration is the sum of baseline corticosterone

and the corticosterone increase in response to the standardized stressor, and both

components were similarly associated with male survival in a model that included both

variables. This implies that baseline corticosterone itself also exerts an effect on male

survival, but this was only revealed when the stress-induced corticosterone increase

was included in the model, presumably because this increased statistical power.

5. Given that corticosterone concentrations are highly repeatable in our study population

and independent of manipulated foraging conditions, these data suggest that

endocrine stress reactivity may be a major component determining male life span,

presumably also in wild populations.