Effect of age, breeding experience and senescence on corticosterone and prolactin levels in a long-lived seabird: the wandering albatross.

Although several studies have described age-specific pattern of breeding performance, physiological and endocrine mechanisms underlying the variation in reproductive success in relation to age are poorly understood. We described baseline levels of: (1) corticosterone, which can trigger nest desertion when secreted at high levels, and (2) prolactin, a hormone known to trigger parental behaviour in incubating known-aged (7-39 years old) wandering albatrosses (Diomedea exulans). In this long-lived species, reproductive performance increases with age and breeding experience before it stabilizes in middle-aged individuals and declines in senescent individuals. We found that breeding experience was a much better statistical predictor of hormone levels than age. Baseline corticosterone levels slightly increased with advancing experience and reached maximal levels about the sixth breeding attempt. Similarly, prolactin levels were positively correlated with breeding experience in males. No such relationship was found in females, but first-time breeding females had lower prolactin levels than experienced females. This parallel increases in hormonal levels with advancing experience could result from improvements of skills, development of an endocrine system adapted to energetic constraints of reproduction or may mirror a higher investment in reproduction. Corticosterone levels decreased in senescent birds, but such a decline was not observed for prolactin. Low corticosterone levels in senescent birds could be associated with a lower ability to secrete/sustain elevated corticosterone levels or with a decreased parental expenditure.