Giraffes (Giraffa camelopardalis giraffa) live in a fission-fusion
social system, characterized by the splitting and reunion of
subgroups within a larger social network. Adult bulls show a
roaming tactic to search for fertile females, whereas younger
bulls are often seen in all male groups.
In this study we combined behavioural observations with
hormonal data. Therefore, a giraffe population of about 80
individuals (11 adult males, 28 adult females, and 32 juvenile
/ sub-adult animals) was monitored six days a week from
dawn to dusk for a period of 12 months (Nov 2014–Oct 2015).
Giraffes were individually identified by their unique pelage
pattern and adult bulls assigned to age classes based on
their appearance (A, B, and C), with class A bulls being the
oldest and tallest. A total of 790 faecal samples were collected
and analysed for faecal androgen (fAM) and glucocorticoid
metabolite (fGCM) concentrations. Class A bulls show significantly higher fAM levels compared to
younger bulls, with lowest fAM levels found for the juvenile /
sub-adult group. Longer periods of increased fAM levels in the
oldest bulls mainly occur during summer and are associated
with an observed birthing peak. Within class A, fAM levels of bulls
in all male groups are significantly lower than when associated
with females, however, these levels are still significantly higher
compared to respective fAM levels from youngest males.
No significant differences in overall fGCM levels could be
found between the different age classes. However, within
class A the bulls show a trend for higher fGCM levels when
sexually active compared to when associated with an all-male
group. In contrast, juvenile / sub-adult bulls show highest
fGM levels when they are in all-male groups, which is possibly
linked to intrasexual competition as younger bulls still need to
establish their position within the hierarchy.
Poster presented at the University of Pretoria, Faculty of Veterinary Science Faculty Day, August 25, 2016, Pretoria, South Africa.