Little is known on the giraffe’s reproductive behaviour, particularly observations of male sexual behaviour are scarce. Most information results from studies on captive animals, and observations of free-ranging giraffes were mainly focused on social structure within herds and only yield limited data on the bulls‘ tendency of roaming between cows’ herds. In addition, no data was available on endocrine mechanisms which modulate male reproductive behaviour. Male endocrinology in terms of androgens has only been studied on culled animals, hence no results correlating behaviour and individual androgen concentrations were available so far.
Simultaneous observation of behaviour and endocrine state has become an important tool to monitor reproduction of wildlife species and has brought up valuable information on the reproduction in different species. Non-invasive techniques to monitor endocrine functions facilitate studies of physiological factors, and play an increasingly important role because it is not necessary to interfere with the animal’s natural behaviour. In this study, the reproductive behaviour of free-ranging giraffe bulls was monitored synchronously with changes in androgen levels using an Enzyme Immunoassay for non-invasive measurement of faecal androgen concentrations. Hwange National Park (HNP), Zimbabwe, was chosen as a main study site, as it is considered to represent near-natural conditions for the local abundant giraffe population. Behavioural observations were conducted on different classes of mature giraffe bulls in 2011. Additionally, faecal samples for hormone measurement were collected in Entabeni Game Reserve (EGR), South Africa, in order to compare between different populations and to increase sample size for assay validation. Sampling in Entabeni Game Reserve was executed twice, in spring and in autumn (2011) in order to investigate on differences in androgen concentrations between seasons.
Behavioural data of a total of 77 individually recognizable male animals were recorded using a specifically compiled ethogram, which covered a range of presumably sexually orientated and not-sexually orientated behavioural patterns.
During behavioural observations faecal samples were collected in order to assign samples with individual mating and dominance behaviour. Samples analysed on testosterone (T) and epiandrosterone (EA) concentration at the laboratory facilities of the Endocrine Research Group, Faculty of Veterinary Science. Behavioural data in respect of obviously sexually orientated actions and dominance state were then compared to faecal androgen metabolites in order to investigate on a correlation between endocrine milieu and reproductive behaviour. By comparing EA levels from mature bulls, mature cows, and immature individuals collected in HNP and EGR, an EIA could be identified which reliably measures androgen concentrations in giraffe faeces. Regarding recorded sexual activity patterns of different age classes, the oldest bulls showed to engage significantly more often in sexual behaviour than younger age classes. Accordingly, faecal epiandrosterone concentrations differed significantly regarding age classes of mature bulls. Furthermore, differences between sample sets indicated EA variations between seasons.
This study was conducted in order to contribute to the understanding of the giraffe’s mating system and male mating strategies in particular. The outcome advocates for future long-term studies in order to investigate on seasonal and ecological influences on the reproduction of giraffe.