Breeding Biology of Silvery-Cheeked Hornbill

Abstract

INTRODUCTION SOME account of the breeding of this hornbill has already been given (Moreau, 1936), with special reference to the building process. It was based on observations, totalling about four hundred hours, made at two nests in the evergreen forest of the East Usambara Mountains, Tanganyika Territory, latitude about 60 south. Since that account was published, and the information it contained compared with that available for other species of African hornbills (Moreau, 1937), further information, which provides a more nearly complete picture of the curious breeding biology, has been accumulated as a result of three more years' experience of the birds. During that period six hundred hours' records have been amassed, mainly by African observers working under our direction at the two original nest-holes and one other. The value of such Africans, able to write Swahili and costing little more than one penny an hour, has been stressed elsewhere. Their standing instructions are to note only the simplest routine items, such as the times of arrival and departure at the nest, but as they get interested they make on their own initiative other notes that often lead to an extension of the original investigations. It may be useful to recall certain facts already recorded about this hornbill, which is an arboreal species characteristic of the mountain forests of eastern tropical Africa. The male, comparable i? size with a Muscovy Duck, is distinguished from the smaller female also by his prominent casque, which is parchment-like in both color and consistency. For breeding, the birds which appear to pair for life, select a hole high up in some great tree and, like the other arboreal hornbills of Africa, constrict the entrance with plaster until only a slit wide enough to admit the bill is left. In Bycanistes cristatus all the actual plastering is done by the female, sitting inside the hole and using material produced by the male in the form of regurgitated pellets of soil. These he presents to her one by one in the tip of his mandibles, in sequences of up to four dozen at a visit. The pellets are apparently prepared in the male's gullet, with the aid of copious salivation, but the actual process is one that needs to be elucidated because it has been shown that the lumps of soil swallowed must be divided, and not merely rounded, after the male has swallowed them. Dr. P. R. Lowe has recently been good enough to make an anatomical examination of the necks of specimens obtained for the purpose, and he informs us