The role of prolactin during incubation: Comparative studies of three Diomedea albatrosses

There is much recent evidence that prolactin is an important influence on parental and incubatory behaviour in birds. In this study prolactin was measured at various stages of the breeding cycle in three closely related albatrosses (the wandering albatross Diomedea exulans, the grey-headed albatross D. chrysostoma, and the black-browed albatross D. melanophris). Each species is monogamous, laying one egg, with the sexes sharing parental duties, including lengthy incubation shifts. In experiments where blood samples were taken daily throughout single incubation shifts (of both sexes) and every 3 hr for 36 hr, high prolactin levels were observed, but there was no indication of any changes that might suggest direct relationships between the hormone concentrations and incubatory behaviour. However, high prolactin levels were characteristic of the whole incubation period with a significant decline in concentrations towards the end of the brood-guard period. The timing of the decline in prolactin levels remained constant, even when the incubation period was artificially lengthened or shortened, as did the overall duration of the incubation-brood-guard period. Further experiments eliminated the possibility that the secretion of prolactin was a response to tactile stimulation of the brood patch by the egg. These results suggest that the incubation period is not endogenously timed but that prolactin may still affect the overall duration of the incubation-brood-guard period, although having little or no effect on the number or duration of incubation shifts

Corticosterone secretion through long incubation shifts in Diomedea albatrosses

Blood samples were collected from free-living incubating Diomedea albatross during single incubation shifts, both daily (wandering albatross D. exulans and every 2 days (grey-headed albatross D. chrysostoma and black-browed albatross D. melanophris), and the concentration of corticosterone was determined. Within 48 hr a significant increase in the corticosterone concentration was observed in each species. The magnitude of the increase was greater in the grey-headed and black-browed albatrosses than in the wandering albatross. Corticosterone concentrations rose steadily through the incubation shift in grey-headed and black-browed albatrosses, but fluctuated erratically in wandering albatrosses. All three species of albatross fast during incubation and the increase in adrenocortical activity is probably related to the voluntary deprivation of food and water

Reproductive endocrinology of the Wandering Albatross Diomedea exulans in relation to biennial breeding and deferred sexual maturity

The reproductive endocrinology of the Wandering Albatross Diomedea exulans was studied at South Georgia to investigate the potential endocrine correlates of biennial breeding and of the acquisition of sexual maturity. Gonads of breeding birds and of known‐age immature birds of both sexes were examined by laparoscopy throughout the period that they were at the nest site. Blood samples, subsequently analysed to determine concentrations of luteinizing hormone (LH), prolactin, progesterone, testosterone and oestradiol‐17/i, were obtained from samples of breeding birds of both sexes at regular intervals from first arrival until the chicks fledged nearly a year later. Before laying in December, breeding birds had mature testes and ovarian follicles and high concentrations of LH, prolactin and sex steroids. Gonadal regression and a rapid drop in hormone levels (except for LH in females) occurred in early incubation (January). Testes (and follicles to a lesser extent) enlarged in mid‐incubation, coinciding with high levels of LH and increases in prolactin and testosterone. Gonads finally regressed completely near hatching time. LH, prolactin and testosterone remained at low levels throughout chick rearing (April to November), but females had several periods of active progesterone and oestradiol secretion, and progesterone was detectable in males only late in the chick‐rearing period. Although some changes in hormone levels are difficult to explain, the patterns are fairly typical of temperate birds. The persistence of progesterone secretion in both female breeders and non‐breeding ‘immature’ birds is viewed as part of a mechanism inhibiting an ovary from becoming vitellogenic. Although testis size and testosterone concentrations increased with age in immature males (of ages 4–10 years), birds of 5 years and older are probably physiologically mature, even though breeding does not start until they are 7 years of age and only half an age group has bred by an age of 11 years. Immature females (of age 4–7 years) had undeveloped follicles, very low oestradiol concentrations but high progesterone levels, providing further support for the role of this hormone in inhibiting gonadotropin secretion. The condition of the female is therefore probably decisive in determining when a pair first attempts to breed but it is unknown what factors initiate normal ovarian development

The endocrine basis of deferred sexual maturity in the wandering albatross, Diomedea exulans. L.

1 Earlier work with albatrosses led to the hypothesis that a critical element influencing ovarian development each year is whether the ovary responds to rising gonadotrophin secretion by secreting progesterone or oestradiol. In the former case no vitellogenesis occurs, the ovary does not mature and no egg-laying occurs. In the latter case ovarian growth and ovulation occurs. This `switch' between progesterone and oestradiol secretion may be important not only for the breeding frequency of adult birds but also prepubertally, influencing the onset of sexual maturity. This paper tests some of the underlying endocrine responses experimentally using known-age (4-11 years old) wandering albatrosses, Diomedea exulans L., at South Georgia. 2 Experiments using birds before and after bouts of sexual display discounted the possibility that high progesterone levels were an artefact of behavioural interaction. 3 Examination of the pituitary-ovarian axis, by injection of ovine luteinizing hormone (LII) and LH-releasing hormone, confirmed that the ovary does secrete progesterone, and that only progesterone is produced in immatures, unlike breeding birds in which oestradiol is also secreted. 4 In terms of endocrine status, female D. exulans were divisible into three main groups: younger (7 years) and last-time non-breeders. These categories were consistent with behavioural data from the same population. Thus the earliest age of breeding is 7 years, display rates increase after `physiological maturity' is attained but decrease once stable pairs are formed and attendance ashore prior to maturity does not influence the time taken to start breeding