206 | SOUTHERN GROUND-HORNBILL, OPPORTUNISTIC HAMERKOP NEST TENANT

206

Art. # 206

OPPORTUNISTIC HAMERKOP NEST TENANT

Southern Ground-Hornbill

Text by Stefan Rust

Photos by Ute Von Ludwiger

2014

(In terms of the Geneva Convention the copyright of these texts belongs to Stefan Rust)

                                                                           Female and Male (from left to right)

These large hornbills, regarded as largest species of hornbill in the world, can live in groups from 2 to 11 individuals. One such group contains a dominant pair, and often more than one adult male along with several immature birds, but mostly only one adult female. They are capable of catching prey as big as hares, snakes and even large tortoises. As their name suggests they spend a lot of time on the ground, about 70% of the day.

The more or less constant food supply in the habitat allows them to live there in groups throughout the year. This habit of living in groups year round made this species a so-called obligate co-operative breeder, meaning the breeding pair never raises its chick alone, but is helped by other members of the flock. A suggestion to this behavior is that the helping skill gained through being a juvenile helper is essential for rearing own chicks as an adult. Mating takes place from September to December, the beginning of the wet season, and two eggs are usually laid in a cavity of a dead or live tree, less often in a cliff hollow and rarely in an earth bank or on an old stick nest.

Female on Hamerkop nest

Recently Mrs. Ute Von Ludwiger was, with a visit to the Chobe National Park, lucky enough to observe and photograph a pair of Southern Ground Hornbill on a deserted Hamerkop nest, usually being built out of sticks, stalks, twigs, reeds and grass. Although this habit of trying to or nesting on old stick nests is considered as rare, it is possible that this behavior might occur more often in areas where reduced nest availability occurs because of fire, logging or as in the case of in the Chobe National Park because of unnatural high elephant populations (more information on this subject in article 197 in Birds in Words www.birdscontour.blogspot.com). In professional jargon a bird species, that takes advantage of the efforts of another species, rather than building their own nest, is described as opportunistic tenant. Southern Ground-Hornbills lay two eggs but under natural conditions siblicide ensures that only one nestling is ever fledged. The first hatched chick, being stronger thanks to the time advantage, overpowers the weaker second hatched chick, ensuring that it first receives the food delivery. Usually this leads to the starvation of the weaker chick within the first week of its life. The question arises why these birds, where siblicide occurs, spend the energy in producing and laying a second egg in the first place? The second egg is laid as a security purpose, should one egg get lost due to whatever reason, the parents have a second chance. But they cannot divide their energy on feeding and protecting two chicks at the same time.