About Geronticus calvus (Boddaert, 1783)
The southern bald ibis, scientifically named Geronticus calvus, is an uncommon bird that is endemic to the highlands of southern Africa. In South Africa, this species’ total breeding population was once estimated at around 4,600 birds. As of the 2020s, the total global population is estimated to be between 6,500 and 8,000 individuals, with a breeding population of 1,600 to 2,000 birds. Little is currently known about the biology of this species. Its body plumage is dark green, marked with iridescent streaks of green, violet, and bronze. The neck bears long blue-green feathers. Adult individuals have copper-colored plumage on their shoulders, while juvenile southern bald ibises have predominantly dull grey plumage. The species’ scientific name Geronticus calvus translates to “bald, old man”, which refers to the bird’s featherless, wrinkled head and face. The bird’s bare whitish head skin is the key identifying feature of this species. It has a red, dome-shaped crown on the top of its head. Its bill is down-curved and red, and its legs are also red. The eyes are colored orange-red. The southern bald ibis has a very restricted geographic range. It is confined to the eastern highland and mountainous regions of South Africa, and its range extends from the highlands of Lesotho into Eswatini. It only makes short-distance movements within its established home range. This species is a cliff-nester, and breeds on open mountain face areas, river gorges, and sometimes around waterfalls. Its breeding habitat is primarily mountainous grassland, located at altitudes between 1,200 and 2,000 meters above sea level. This grassland is classified as “sour”, because its foliage has low nutritional value in late summer and early autumn, after grazing by mammals. Southern bald ibises nest on cliff ledges, and breeding observations are hard to collect because most of these nesting sites are largely inaccessible. Most colonies breed together, but some breeding pairs nest separately from the main group. Females lay their eggs between late July and mid-October. Young birds develop flight feathers between mid-October and December. Nests are built mostly from sticks and grass, and nest building typically begins around two weeks before the first egg is laid. After the first egg is laid, incubation lasts between 26 and 32 days. Incubating adults change position and rotate the egg more frequently starting around three days before the egg is due to hatch. After hatching, chicks are fed by regurgitation from their parents for the first 7 to 10 days. Young birds leave the nest to wander around after 35 days, and gain the ability to fly between 40 and 50 days after hatching. Even after they can fly, juveniles still spend most of their time on cliff ledges or in the nest.
