It takes cooperation to raise young and keep them safe in the bush
Members of a Southern Ground Hornbill family group take on different roles in order to raise chicks. Family members also must cooperate to defend territory or risk young members being kidnapped by rival hornbill groups.
We often see Southern Ground Hornbills when we traverse their territory in Kruger National Park. We also hear their distinct calls during mating season in May.
Ground Hornbills are Cooperative Breeders with all members taking on responsibilities
Ground Hornbill groups typically consist of a single adult female, several adult males, and immature birds. Each group also has an alpha male who is usually considered the one who mates with the female. Once the eggs are laid, the female has the sole responsibility of incubating them in the nest for around 40 days, during which time the rest of the group will bring her food from the outside world. Once the incubation period is over, she leaves the nest to join the rest of the groups and begins to play her part in feeding the chick.
Studies have shown that the ages, sex, and rank determine the roles of each individual in the group. The contributions of the parent birds will depend on the number of helpers they have. Typically, there are two variations: additive care and compensative care. Additive describes each bird in the group doing an equal part in feeding the chick.
With compensation care, some adult birds, usually the parents, neglect their feeding duties and rely on other members of the group to feed the chicks. This happens in cases of larger groups where there are more birds to do the feeding.
Juveniles are do not participate in territory patrols for fear they will be kidnapped by rival hornbill clans.
Territory defense is vital to the survival of ground hornbills. Each group is dependent on its nesting site and food source and the birds must be ready to fend off any intruders. Their deep booming calls which travel a great distance and are a signature sound of the bush, broadcast who they are and where they territory lies.
Patrolling and defending these territories ( up to 100 sq.KM) requires an immense amount of effort and energy. You would assume an important job such as this would be performed by all members, but it has been observed that younger individuals within groups do not take part in territorial defense. It is the responsibility of just the adult birds. The reason why is not understood, however the recent observation of kidnapping of juveniles by opposing groups has suggested that there is a risk of losing young members of the group in a territorial altercation.
Breeding is difficult (and getting harder) for ground hornbills and kidnapping a healthy juvenile is a cheap way to grow the clan and perhaps replace chicks lost to failed breeding or rearing.
