One writer states, "Their industry seems almost equal to that of the bee. Throughout the day they appear to be busily employed in carrying a fine species of grass, which is the principal material they employ for the purpose of erecting this extraordinary work, as well as for additions and repairs.
"Though my short stay in the country was not sufficient to satisfy me, by ocular proof, that they added to their nest as they annually increased in numbers, still from the many trees which I have seen borne down by the weight, and others which I have observed with their boughs completely covered over, it would appear that this really was the case.
"When the tree which is the support of this aerial city is obliged to give way to the increase of weight, it is obvious they are no longer protected, and are under the necessity of rebuilding in other trees.
"One of these deserted nests I had the curiosity to break down, so as to inform myself of its internal structure, and I found it equally ingenious with that of the external. There are many entrances, each of which forms a separate street with nests on both sides, at about two inches from each other."
Livingstone gives the following description of a curious bird called the korwé: "We passed the nest of a korwé just ready for the female to enter. The orifice was plastered on both sides, but a space was left of a heart shape, and exactly the size of the bird's body.
"The hole in the tree was in every case found to be prolonged some distance upward above the opening, and thither the korwé always fled to escape being caught.
"In another nest we found that one white egg, much like that of a pigeon, was laid.
"The first time that I saw this nest I had gone to the forest for some timber. Standing by a tree, a native looked behind me and exclaimed, 'There is the nest of a korwé.' I saw a slit only, about half an inch wide and three or four inches long, in a slight hollow of the tree.
"Thinking the word korwé denoted some small animal, I waited with interest to see what he would extract. He broke the clay which surrounded the slit, put his arm into the hole, and drew out a red-beaked hornbill. He informed me that when the female enters her nest the male plasters up the entrance, leaving only a narrow slit by which to feed his mate, and which exactly suits the form of his beak.
"The female makes a nest of her own feathers, lays her eggs, hatches them, and remains with the young till they are fully fledged. During all this, which is stated to be two or three months, the male continues to feed her and the young family. The prisoner generally becomes quite fat, and is esteemed a very dainty morsel by the natives, while the poor slave of a husband gets so lean that, on the sudden lowering of the temperature which sometimes happens after a fall of rain, he is benumbed, falls down, and dies.