Breeding the Abyssinian ground hornbill at San Diego Wild Animal Park

Summary The observations recorded during the three nestings at the San Diego Wild Animal Park make it possible to construct a growing picture of the nesting habits and requirements of the Abyssinian ground hornbill. It is of some importance to mention that at no time did we offer or construct any artificial potential nest sites. All sites utilized were chosen by the birds alone. The hornbills seemingly prefer to construct their nests in a bank of hardpacked yet workable soil. Sandy, rocky or other intermediate sites, including several available logs, were investigated but rejected. The man-made culvert chosen in the preliminary nesting attempt was also located in the same hard-packed material as the later two successful nests. The nest itself was carved out using the beak to break the soil loose, and the feet to scratch and push the loosened material from the growing hole. Both finished nests had approximately the same dimensions and were constructed in such a manner that direct sunlight never penetrated beyond the entrance. The floors were concave and covered with a litter composed of dead leaves, grasses and small twigs. Excavation of both sites took approximately two weeks. Prior to the selection of the nest site, the adult birds exhibited so-called ‘searching behaviour’, which subsequently led to their thorough examination of suitable locations within an established ‘home’ or preferred range where they spent most of their time. Simultaneous with the appearance of searching was the ♂ s frequent presentation of food to the ♀. Once a suitable site was found, searching was replaced by digging, which in turn, with excavation completed, was supplanted by collection and arrangement of litter within the nest. The ♂ did most of the collecting and carrying and the ♀ arranged it until the floor was covered to a depth of 7–9 era. Although mating was observed only once, it is assumed from the birds' general behaviour that it occurred frequently before the ♀ laid one to two chalky white (c. 8 × 5 cm) eggs. Unlike other hornbill species, the ♀ ground hornbill was not walled into the nest nor was there any evidence that she moulted. After a 37–40 day incubation period, blind, naked chicks with purple-grey skin were hatched, the second egg in all observed instances taking slightly longer, 39–40 days, to hatch. The chicks grew rapidly and left the nest after about three months. At the time of their emergence, they were fully capable of flight, but beak, general body size and plumage had still to develop further. External sexual dimorphism was also first apparent at this time, although it was not until the second chick emerged from the nest that we could compare the two. The latter had a definite reddish cast to its gular sac, the distinguishing feature of the ♂abyssinicus, while the sac of the first chick was grey. The second chick was also considerably larger than the first, another indication that they were of opposite sex. While the ♀ was incubating, she received all her food from the constantly foraging ♂ and continued to do so until 10–12 days after hatching. Then she left the nest for brief, but progressively lengthening periods and began to forage for herself, although still dependent on the ♂ for part of her food. The ♂ was also sole provider to the chicks, either giving food to the ♀ who in turn fed the chicks, or, once the ♀ had left the nest, feeding them directly.