We were relaxing at our campsite at Palmwag, in the Damaraland area of Namibia, when we noticed a lone Southern yellow-billed hornbill (Tockus leucomelas) energetically flitting to-and-fro across the dry river bed that fronted our campsite. It didn’t take long for us to realise that his attention was focussed on one particular tree on the far bank of the river and we watched his activity more carefully. This closer attention revealed that the bird’s short forays followed a definite pattern – he would fly off in a fairly random direction, stay away for a few minutes and return to the same spot in the same tree, alighting on a branch for a moment or two before dropping down to the trunk of the tree.
During one of his excursions we nipped across the river to see the object of his attentions. As we suspected, we found that his mate was walled up into a nest in a hollow section of the tree trunk.
The opening to the nest, just a narrow vertical slit through which the male could pass food to the female, was about one-and-a-half metres above the ground and although we didn’t want to interfere with the process by getting too close, we thought that we could see movement in the dark interior of the nest.
The male was tireless in his efforts to provide food and we wondered if there were fledglings in the nest, or if a very hungry female was still incubating the eggs. We watched the male taking lizards or geckos to the nest, and in the early morning when there was a collection of grasshoppers enjoying the sun on the wall of the camp ablution block, he made several trips between this spot and the nest to make the most of the bonanza. Although hornbills are largely fruit eaters, the male was clearly not averse to feeding his mate (and possibly her brood) on lizards and grasshoppers during this period. His hunting prowess was admirable, and the trips were completed very quickly.
Southern yellow-billed hornbills are monogamous birds, and, like the example described above, often nest in hollow trees, closing the female into the nest with a wall of mud mixed with their own faeces, for the duration of the incubation period. The female lays a clutch of three or four eggs a few days after being walled in, and these take approximately 24 days to hatch. The chicks are not ready to leave the nest for another 45 days or so, although the female will break out of the nest before this as the nest becomes too crowded. During the time the femle is inside the sealed cavity, she will undergo a complete simultaneous moult, perhaps triggered by the darkness of her nest, and this is in contrast to the sequential moult of males and non-breeding females.
Unfortunately we didn’t stay at Palmwag long enough to find out the outcome of this breeding episode, but we were certainly impressed with the efforts that the male hornbill put into providing for his family.