19 1 8.] by 6irds of Eggs unlike their oivn. 129 



of its clutch of three, for I had taken one previously, yet, 

 although the eggs were fresh, it continued to incubate it and 

 reared a young bird which gave me some very interesting 

 tongue observations. Very numerous similar instances 

 occurred throughout the experiments, and suggested that 

 we need not regard a Cuckoo's egg found in a nest as 

 quite necessarily finally accepted. The bird's first object 

 seemed usually to be to warm the eggs, and attention to 

 the intruder was postponed. 



3. Nor ivas the acceptance necessarily always voluntary. — 

 A Layard's Bulbul with three eggs of the type shown in 

 fig. 16 rejected a Weaver's egg of the type shown in fig. 9 

 of the same plate. One- of the BulbuFs remaining two 

 eggs was then replaced by a pigeon-like egg of Centrojms 

 burchelli. First one Bulbul returned and perched beside the 

 nest ; then its mate arrived and perched on the edge. The 

 first flew off, but the second stood gazing at her new and 

 enormous acquisition, motionless, for approximately one 

 minute. Then she slipped down on to the nest and sat ! 

 I waited for a considerable time, and, as she did not stir 

 and it was now getting dark, I left. Next afternoon the 

 nest was pulled down a good deal on one side. The weight 

 of the Centrojms egg would not have done it alone, as the 

 nest had been firmly placed. That egg was still there, 

 but the Bulbul's egg was gone and a minute search below 

 the tree failed to produce any trace of it. On another occa- 

 sion a Stonechat [Pratincola torquata) adopted a Shrike^s 

 egg [Lanius collaris humeralis) given her in place of one 

 of her own three. Several days later she was still sitting 

 on it. I now replaced a second of her eggs with another 

 Shrike's egg. When I revisited the nest it was deserted 

 and the Stonechat's egg was gone, the two Shrike's 

 remaining in possession. I am inclined to believe that 

 the Bulbuls and the Stonechats of the above observations, 

 finding the substituted eggs beyond their powers of 

 ejection, accepted it perforce for the time being, and 

 later removed their own egg. The distortion of the 

 Bulbuls' nest may have resulted from a previous effort 



SER. X. — VOL. VI. K 



