Patterns of faecal hormone metabolites associated with reproduction in cinereous vultures Aegypius monachus

Abstract

Cinereous vultures Aegypius monachus are listed as Near Threatened by the IUCN. Breeding efforts in zoos have had limited success and little is known about the species’ reproductive biology. Here, patterns of faecal gonadal hormone metabolites associated with egg-laying for cinereous vultures are described. Glucocorticoid metabolites were also measured to assess the relationship between stress and egg production. Faecal samples (n=2012) were collected from 34 cinereous vultures at 14 institutions. Using enzyme and radioimmunoassays, concentrations of faecal oestrogen, progestogen, androgen and glucocorticoid metabolites were quantified. General linear models were used to assess differences in concentrations in relation to egg-laying, sex, age, month, housing conditions and rearing history (hand or parent). Metabolite concentrations did not vary in relation to housing, rearing or age. Of the 10 breeding pairs, 7 produced an egg and 1 pair hatched a chick. Oestrogen and progestogen metabolites were higher in laying females and concentrations of both metabolites increased prior to egg-laying. In contrast, androgen metabolites were lower in males whose partner laid an egg. Glucocorticoid metabolite concentrations did not vary in relation to egg production. Oestrogen and progestogen metabolites of laying females were highest in March, while glucocorticoid metabolites of both males and females were highest in January and declined during the following months. No monthly trend in androgen metabolite production was observed. This study provides new endocrine data for cinereous vultures and confirms that faecal hormone analysis is an effective way to monitor egg-laying and monthly changes in hormone levels.