19 1 8.] by Birds of Eggs unlike their otvn. 139 



which one or two eggs might have been removed by some 

 tender-hearted collector. 



However, the indirect evidence^ which I shall refer to 

 below, seems sufficiently strong. 



Other results of our not seeing all the eggs that are re- 

 jected would be, I think, to make it difficult always to be sure, 

 except on ovarial evidence and observation of behaviour, 

 (1) of the duration of the laying season of particular 

 birds — it might extend beyond that of the special host, but 

 the eggs then laid would be mostly eliminated before being 

 seen — or (2) of tlie total number of eggs laid. This is likely, 

 I think, always to be distinctly larger than the number of 

 eggs found by an observer and correctly attributed by him 

 to a particular bird, unless we can assume not merely that 

 the observer has found all the eggs laid but that the Cuckoo 

 will have beeu successful in matching all her eggs. 



Discussion. 

 T. Methods of dealing with the Cuckooes egg. — I have 

 already shown that the removal of the interloper was the 

 method adopted by nearly all the birds on which I experi- 

 mented, that it was usually, apparently, carried right away, 

 as are excreta, that it was sometimes spiked and that, in one 

 experiment, it was merely dropped, after spiking, outside the 

 nest. Of the two eggs treated thus, one was probably too 

 heavy for the biid to carry, the other not, and another bird 

 of the same species that was experimented on with a light 

 egg apparently carried it away, for it could not be found. 

 I have already referred to the alternative course, probably 

 followed where the substitute was large. Practically no 

 definite desertion of the bird's own eggs took place, even 

 though some parents were reduced to sitting on a single egg. 

 The Flycatcher, Bradyornis murinus, seemed to be an ex- 

 ception, three nests in succession being deserted, eggs and 

 all — in one case after a substitute had been ejected, in the 

 other cases after I had merely visited the nests. In a few 

 cases all the eggs in a nest, substitute and host's eggs, 

 disappeared, and this may have sometimes occurred through 



