NO. 9 CASQUED HORNBILLS KILHAM 25 



the pair of hornbills were working on their nest late in the afternoon. 

 An adult male kept coming into the tree and the male in possession 

 repeatedly drove him away. By November 8 the female was walled 

 in, and a more serious attempt at interference was now made by a 

 foreign female. I first noticed her on November 19. She was follow- 

 ing the male and lighted in the nest tree when he lighted above his 

 nest hole. On November 23 the same course of events took place, 

 except that the male was less tolerant. He fed his own mate, then 

 drove the intruder away. A week later I again saw her fly in close 

 behind the male and light 25 feet from the nest hole. The male gave 

 his mate a piece of bark followed by some fruit, and then bounced 

 from one branch to another toward the foreign female. The intruder 

 called and the female within the nest screamed a number of times. 

 I wondered whether the interloper could seduce the male, but from 

 subsequent observations it seemed unlikely that she would. The male 

 returned again to the nest hole, and a few minutes later was in the 

 upper part of the tree knocking about on dead branches until he dis- 

 lodged a piece of bark. He clamped his bill on the bark until it was 

 largely fragmented. Then he moved toward the foreign female. H he 

 presented the bark, one would suppose that she had some attraction 

 for him. After a moment, however, he changed his direction, flew 

 down to the big limb below, bent over the nest hole, and gave the 

 token to his mate, accompanied by a feeding chuckle. Subsequently 

 he returned to perch quietly within 8 feet of the intruding female. 

 At 7 :30 a.m. the two of them flew away together. As the nesting 

 season progressed, he became less tolerant of her intrusions. On my 

 next visit, a week later, he made several swoops in an effort to drive 

 her away, but she was not discouraged. On February 3 I again 

 watched her fly in behind the male and alight in the nest tree, making 

 considerable noise. The male stopped feeding his mate, swooped at 

 the interloper and drove her down toward the ground. However, 

 when he flew away, she followed a short distance behind. It generally 

 appeared that her interest was in him rather than in the nest. On 

 March 2 I observed a more serious situation. Late in the afternoon I 

 found a foreign female clinging to the nest entrance. This time she 

 was alone. She worked industriously, removing debris from the en- 

 trance and knocking from the cement wall chunks which she broke 

 in her bill before dropping them. There was no noise. After 5 minutes 

 the male arrived and she flew a short distance away. He tossed some 

 debris from the entrance, then drove the foreign female to another 

 tree, flying at her so hard that he knocked leaves from intervening 

 branches. He returned to his nest with a small stick held like a cigar. 



