Don't forget the Northern or Abyssinian Ground-Hornbill!
There are two species of the ground hornbill genus Bucorvus that live in the sub-Saharan savannas of Africa with ranges that only just overlap along the equator in Kenya. This whole website is directed at conservation of the Southern Ground-Hornbill (SGH) B. leadbeateri, but we should not neglect the Northern or Abyssinian Ground-Hornbill (NGH) B. abyssinicus. It has been much less studied but may also need conservation attention given the extensive degradation and/or transformation of savanna habitats reported from across its range. As its scientific name suggests, the NGH occurs in Ethiopia (previously Abyssinia), from where its distribution extends east to Senegal and south to Uganda and Kenya. Both species occupy a wide range of altitudes, the NGH up to 3,257 m a.s.l. in the Simian Highlands of Ethiopia, but generally the NGH extends into drier and more rocky savanna and steppe, apparently with larger home ranges of 260 km2 reported. Its current range places it midway between that of the SGH and two fossil ground hornbill species found in Late Miocene deposits (5.3-11.6 million years ago) in Morocco (B. brailloni) and Bulgaria (Euroceros bulgarius), at a time when savanna and grasslands extended across the Sahara and into southern Europe.
What they look like:
Although the NGH looks very similar to the SGH from the neck down - all-black plumage except for white primary feathers evident in flight - it differs in a number of anatomical and behavioural details. The head, neck and bill of the NGH seem more slender and the bill less curved, which suggests less emphasis on digging for food. The wings also seem broader and longer, which suggests more buoyant flight. The bill has a unique triangular deep-yellow/orange patch at the base of the upper mandible, which might be coloured by preen oils from the well-feathered preen gland at the base of the tail. The most distinctive feature of this species is the raised cowl-like casque atop the bill, with prominent ridges along its sides and what looks like a cut-off opening at the front.
Adults display their sex by having the bare skin around the eyes and down the inflated throat and neck coloured predominately red in males, apart from a blue throat patch, and all lapis lazuli blue in females, which differs from the predominately red SGHs where only the female has a violet-blue throat patch. The sexes of the NGH are distinguishable from fledging, based on bare skin colours, even though duller and paler in juveniles, which is notably different from SGHs where immatures are quite unlike adults until 2-3 years old, and may only definitively display their sex when about 4-5 years old. In both species, juveniles and young immatures can be distinguished by their smaller bill and casque, especially in the NGH where the casque develops into such a prominent structure.
Group Living or Just Pairs?
Most sightings of NGHs from across their range report the species in pairs, trios or, at most, quartets, which, when carefully observed, have been made up of an adult pair with one or two offspring, with mean group sizes in Ethiopia, Chad and Mali recorded as 2.2, 2.3 and 2.1 respectively. There are reports of groups of up to 10 birds together but, where there is evidence to be examined, at least some are made up of uneven numbers of immatures of either sex (e.g. 5 males + 1 female or 3 males + 7 females), while others are at concentrations of food (but not aged or sexed). The breeding biology of the NGH is virtually unstudied, except in captivity, but overall these group sizes suggest breeding as monogamous pairs without helpers, rather than as obligate cooperative breeders like SGHs in mean groups sizes of about 3.6 (range 2-9), usually with one or more adult helper males. The early display of sexual colours and records of predominately immature groups in the NGH accord with this interpretation, at least until detailed population studies in the wild are attempted.
Otherwise, the general biology of both species is similar. Groups call with four deep booming notes at dawn, walk on the ground for much of the day in search of food, fly only if disturbed or crossing dangerous denser habitat, and go to roost in a tree in the evening. The diet is predominately faunivorous, on small animals ranging in size from insects to such vertebrates as tortoises, but apparently with a larger component of carrion, fruits and seeds than the SGH. Some food is snatched from overhead vegetation, and items may even be cached (at least in captivity), so there may be subtle dietary and foraging differences between the species, with the slender-headed NGH digging less for and snatching more at agile prey items.
There is so far no evidence that NGHs breed other than as pairs without dedicated helpers, even juveniles, unlike the obligate cooperative breeding of the SGH. However, the jury must remain out on this until detailed studies have been conducted on wild populations of NGHs, with odds on that any cooperation found will be facultative at best. Otherwise, the breeding process is virtually identical, initiated with nest inspections and courtship feeding, using natural tree or rock cavities, artificial beehives or baskets, or rarely old stick nest or self-excavated bank holes as sites, and copulating on or near the ground. Baobab (Adansonia) and Ana (Faidherbia) trees or Borassus palm stumps are especially favoured. In the NGH both sexes add lining of mainly dry leaves to the nest cavity, but mainly the male, which differs slightly from the all-male lining reported for SGHs. The nesting cycle is also similar, spanning 118-131 days with 37-40 days incubation and 80-90 days nestling periods, but the spread of egg-laying dates/seasons across its wider range is more variable than for the SGH and in captivity a pair even bred aseasonally, with as little as a fortnight between removal of a fledgling and re-laying. As for the SGH, 1-2 white eggs are laid per clutch, about 5 days apart, but only a single fledgling is so far reported, despite the second-hatched chicks proving viable if removed and hand-reared.
Only the male has been reported delivering food to the nest, where the female performs all incubation and the early part of the chick brooding before emerging more and more to help at 10-20 days post-hatching. The chick hatches with pink skin that darkens to black, but only after about 10 days which is slightly longer than for the SGH and this, linked to the earlier female emergence (30+ days in the SGH), suggests that chick development might be slower and female involvement in its feeding earlier to counter lack of non-breeding helpers at the nest. Once fledged, similar natural predators (once a Martial Eagle) can be expected, but long adult survival to offset this (40+ years for a pair in captivity) is also reported.
The NGH being such a large and obvious bird also attracts human attention, mainly positive, being chased in The Gambia, but only because considered a good omen when seen flying, and generally unmolested elsewhere for various un-described totemic functions. This may explain frequent reports of birds seen on rural croplands and nesting near habitation, maybe further encouraged by availability of beehives or baskets in trees to be used as nests. Some individuals are collected, to camouflage Nigerian (Hausa), Cameroonian or Sudanese hunters when stalking game, the hornbill's head mounted on a stick strapped to the hunters forehead as he advances with torso bare and in a crouching pose, sometimes as a group. Much more anthropological information is expected for the NGH, given the greater variety reported for the SGH (incorporation of calls in traditional sayings, songs, drumming, drought relief and treatments), but this has not to our knowledge been widely researched for the NGH.
Any sponsorship for or collaboration with persons or organisations interested in comparative studies of the NGH and SGH in the wild will be much appreciated.