34 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



DISCUSSION OF FACTORS CONTROLLING HORNBILL 

 POPULATIONS 



Birds such as hornbills which rear a single young one are, one may 

 suppose, relatively safe from enemies. This was probably true before 

 the original rain forests had been cut. A female walled in a nest 70 

 feet above the forest floor, in the trunk of a huge tree without lower 

 branches, is in an almost impregnable position. Such trees, however, 

 are now entirely absent over large areas. Natives' shambas, elephant 

 grass, and patches of second growth cover the countryside, leaving 

 only thin fringes of large trees along lake shore and swamp. Eastern 

 Uganda is good agricutural country and the native population is 

 rapidly expanding. Interference by man's activities is, I believe, the 

 greatest factor limiting hornbill populations. Mpanga Research Forest 

 remains as a needed refuge. Even here, observations suggested that 

 suitable nesting sites were way below the demand. Some pairs of 

 hornbills were nesting in unfavorable situations. For example, nests 

 10 and 16 (table i) were only about 30 feet from the ground and 

 were easy to reach. Also, I continually saw pairs of hornbills that were 

 not nesting during the nesting period. Two pairs tried without suc- 

 cess to build nests in unsuitable locations. When nest 4 suddenly 

 became vacant owing to the death of the male, another pair of horn- 

 bills took it over immediately. Some of the incidents of specific inter- 

 ference already narrated indicate the degree of competition. The 

 disastrous effects of forest destruction on casqued hornbills is well 

 described by Capt. C. R. S. Pitman (1955, personal communication). 

 He writes that "ever since I first went to Entebbe in 1925 forest 

 destruction in the vicinity of Entebbe and Kisubi, and in fact all along 

 the NTB-Kampala Road, has been on such an appalling scale, that 

 annually large numbers of trees, with the best nesting sites, are being 

 destroyed. Byconistes therefore is constantly having to move farther 

 and farther afield to find suitable nesting sites. When I first went to 

 Entebbe there must have been at least two dozen Bycanistes nests 

 within a 2-mile radius . . . but now good nest sites are fewer and far 

 between and Bycanistes resorts to hollows, some readily accessible, 

 which it would have ignored in the past." 



Fortunately Africans in eastern Uganda do not molest birds to any 

 extent. Ease of growing food and comparative prosperity probably 

 puts less pressure on them to do so. But in Bwamba, where hornbills 

 were considered fair prey, I continually came across Pygmies and 

 other natives wandering about with slingshots and small bows and 

 arrows. Under these conditions I found the birds more wary and 

 difficult to observe than near Entebbe. 



