NO. 9 CASQUED HORNBILLS — KILHAM 3 



nest hole (3 nests) ; hearing the feeding chuckle of the male and fol- 

 lowing it through the forest (2 nests) ; rattle of female bill in nest 

 opening (i nest); shrill screaming of female hornbill from behind 

 wall when her nest was approached by foreign hornbills (i nest) ; 

 commotion of a group of hornbills surrounding an eagle (i nest). 

 Two other methods involved observations of a male bird: When on 

 a direct, purposeful flight into the forest (i nest) ; and following a 

 bird after it picked up dirt from the ground (i nest). Finally, one 

 nest located in the Botanical Gardens was first noted by other ob- 

 servers. A helpful clue in finding an actual nest tree, once the general 

 territory had been localized, was the presence of the elliptical stones 

 of Canarium schweinfiirthii on the ground. This fruit is a main item 

 of hornbill diet. Feces were of little help as signs. They are mostly 

 brown in color, disintegrate rapidly on vegetation, and are expelled 

 away from the nest. 



Identification of individuals. — Adult hornbills, as well as young 

 emerging from the nest, have the same pattern of black and white 

 plumage. Males, however, are readily distinguishable from females. 

 As adults they are a third larger and have the huge, forward-projecting 

 casque on the upper bill. Young males, even at time of nest leaving 

 (pi. I, fig. 2), have a larger bill than adult females. There is an ivory- 

 white patch at the base of the upper mandible. As illustrated by my 

 young hornbill (pi. 2, fig. i), this patch is very large and is well 

 supplied with blood vessels. It is probably an area of growth. In adult 

 males it is smaller, but can be seen at a distance and, owing to varia- 

 tions in size and configuration, it proved to be of considerable value 

 in recognition of individual birds. It is unknown at what age a young 

 male develops a forward projection of his casque. 



Watching hornbills. — Observations on nesting hornbills were made 

 from the ground close to nest trees, using 8 x 50 Zeiss binoculars. 

 A few males were shy and rarely seen at the nest. Ordinarily, how- 

 ever, males came to feed their mates if I sat still and waited. A blind 

 was not essential. I usually watched from the spot which gave the 

 best possible view. Along some trails in Mpanga Forest and in the 

 Botanical Gardens the hornbills were accustomed to seeing people 

 passing below. Hornbills were less shy when constructing nests, 

 possibly because of preoccupation with the work. Many nests were 

 inconveniently located. I therefore concentrated my watching on nests 

 most favorably situated. Only one nest was located low enough for 

 construction of a scaffold, reached by ladders tied in place. One 

 could look inside by pointing a flashlight through the aperture. Ob- 



