NO. 9 CASQUED HORNBILLS KILHAM 33 



like a crumpled piece of paper, they stand out partially again. In 

 young birds the feathers just above the eyes and forming the horns 

 are brown. By the age of lo months these are almost entirely replaced 

 by black feathers. 



The bill tip can be used as delicately as a pair of forceps. In fe- 

 males, only the tips may be in apposition, leaving a slightly open space 

 for several inches behind. This space is more exaggerated in older 

 females and may suggest, to a mild degree, the bill of an open-bill 

 stork (Anastomus lamelligeriis). At first I thought the space was due 

 to wear. However, my captive Zika had this space at an early age 

 when wear was not apparent. The bill tip itself is very sensitive. It 

 is, for example, continually used to investigate strange objects. If I 

 give my captive hornbills a fruit they have not seen before, they will 

 toss and squeeze it in their bill tips for some time before swallowing. 

 The bill of the male is huge, and that of a young one is larger than a 

 female's before he leaves the nest. This is shown in the photograph 

 (pi. 5, fig. 2) of two young hornbills, male and female, at 7 to 8 

 weeks of age. Plate 6, figure i, shows Mpanga's bill at 6 months of 

 age and plate 2, figure i, at 10 months. The white patch is apparently 

 an area of growth. With some transillumination one can see that it 

 is full of blood vessels. The patch becomes smaller in older males. 

 No one knows, as far as I am aware, how long it takes the bill of the 

 male to reach full development, with a forward projecting knob. At 

 present I can only speculate on the function of this huge structure. 

 It would appear to have no strictly practical use, for the smaller bill 

 of the female serves more immediate functions. Her bill not only 

 is used to plaster the wall of the nest, but is also a formidable weapon 

 for defending the nest opening. Its inner capacity is no less than that 

 of the male's. In addition, males and females are equally adept at 

 catching small objects with their bills. I wonder, therefore, if the 

 casqued bill is not chiefly sexual in function. Possibly it is com- 

 parable to the mustache stripe of the male flicker or the red breast 

 of the cock robin. In this sense it would serve to release behavior 

 patterns in the female which promote successful breeding and pair 

 formation. 



The feet of hornbills, with three front toes somewhat webbed, do 

 not grasp tightly. I have never felt any real grip from the birds 

 perching on my arm. Hornbills can, however, hang down from a 

 perch, almost parrotlike, without losing their hold. The long tail is 

 remarkable in that it can be neatly folded over the back. This adapta- 

 tion is convenient for females walled within nest cavities, as is the 

 fact that they are a third smaller than males. 



