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BIOLOGY OF THE GROUND-HORNBILLS

 

·       The earliest credible fossil record for ground-hornbills is from about 15 million years ago, from mid-Miocene deposits in Morocco, and then in the late Miocene a second fossil species from Bulgaria. Later, prehistoric tectonic and climatic changes split up the ranges on both the African and European landscapes. Now ground-hornbills face alterations that come from human activity - including rapid, devastating changes both to habitat and to the global climate change, fragmenting many of their habitats and populations into dangerously small units, in this way threatening their survival [1].

 

·    The Southern Ground Hornbill (SGH, Bucorvus leadbeateri)is the largest of the 54 hornbill species that are distributed across  Asia, India and sub-Saharan Africa.

 

·    Bucorvus means ‘large crow-like’ bird and leadbeateri comes from Benjamin Leadbeater (1760-1837), a Victorian naturalist from London.

 

·   These birds are the largest avian species known to be obligate cooperative breeders, and one of only four African hornbills are thought to exhibit this social      organisation [2].  Like most large birds, the Southern Ground Hornbill is sparsely distributed at low densities, defends large territories (about 100 square kms) and has widely spaced breeding sites [3].

 

·    SGHs are large, conspicuous, turkey-sized birds with black plumage and very characteristic red facial skin. They are long-lived birds, and the largest co-operative breeding bird in the world. They live in groups of 2 to 12 individuals that occupy and vigorously defend large territories of up to 100 km2. These groups can consist of either a single breeding pair or a large group with a dominant breeding pair and helpers of various ages.

 

·    SGHs spend most of their day walking slowly and searching along the ground for food. They are predominantly carnivorous, feeding on a large range of insects, reptiles, amphibians and small to medium sized mammals and birds. They feed over a wide range of savannah, grassland and farming habitats.

 

·    The sexes look alike in young birds, but once they are fully mature, the males have fully red facial skin, while the female has a patch of violet blue below the bill, which in some cases can cover most of the lower parts of the facial skin. There are isolated cases of males exhibiting female colouration.

 

·     They are strong but low fliers, with white primary feathers, but are seldom spotted in flight. They roost nightly in large trees at different locations. 

 

·    Ground Hornbills nest high up in large trees with sizable cavities, sometimes in holes on cliffs or earth banks, and rarely on old stick nests. In 80% of clutches, the breeding female lays two eggs and the second egg is laid three to five days after the first. Since incubation commences with the first egg, the chicks hatch 3 to 5 days apart. The older chick may weigh 250g by the time the second hatched chick hatches, at about 60g. The eldest chick always out-competes its younger sibling for food and the younger dies of starvation within a few days of hatching.The critical aspect of Southern Ground Hornbill breeding biology is their naturally low productivity. The birds breed during the austral summer, with egg-laying in September to December, usually after the first good rains [4], but sometimes not every year. On average, attempts to breed are every 2.6 years, but the average overall fledging rate in the Kruger  National Park is only one chick per group every 9.3 years  [5]. 

 

·   In South Africa, the clutch size is one or two eggs, rarely three and they are incubated for about 42 days. Only one chick is ever reared by to fledging by the adults, even in a captive environment when food supply is not an issue [6]. The adult female will brood and feed her chick for the first month, on food delivered to the nest by the group, and only later join the other group members in gathering food. Fledging occurs around 86 days after hatching. It takes six years for a young bird to reach adulthood and it most probably does not start breeding even thenas it first has to become a dominant alpha bird in a group.  It was estimated that the first successful breeding in females in the wild would be around 15-17 years [7], but in captivity they are breeding at 10 years old. It is estimated that they live on average about 45 years, but maybe individually for up to 60 years or longer in the wild.

 

[1] Kemp & Kemp, 2006
[2] Kemp 1995
[3] Kemp 1987, Kemp et al. 1989, Knight 1990 in Msimanga 2004
[4] Kemp & Kemp 1991 in Msimanga 2004
[5] Kemp, 1995 in Msimanga 2004
[6] pers comms Delecia Gunn, 2005
[7] Morrison 2005