Cii.vr. VII. INSTINCTS OF THE CUCKOO. oji 



would assuredly have been added to those Mhich it is assumed 

 must all have been acquired together. The eg-gs of the Aus- 

 tralian ]3ronze cuckoo vary, according to Mr. Ixanisay, to an 

 extraordinary degree in color; so that in this respect, as well 

 as in size, natural selection assuredly might have secured and 

 iixed any advantageous variation. 



With reference to the young European cuckoo ejecting its 

 foster-brothers — it must first be remarked that Mr. Gould, who 

 has paid particular attention to this subject, is convinced that 

 the belief is an error : he asserts that the young foster-birds 

 are generally ejected during the first three days, when the 

 yoimg cuckoo is quite powerless ; he maintains that the young 

 cuckoo exerts, l)y its hunger-cries, or by some other means, 

 such a fascination over its foster-parents, that it alone receives 

 food, so that the others are starved to death, and are then 

 tljrown out, like the egg-shells or the excrement, by the old 

 birds. He admits, however, that the 3'^oung cuckoo Avheu 

 giown older and stronger may have the power, and perhaps the 

 instinct, of ejecting its foster-brothers, if they hapj)en to escape 

 starvation during the first few days after birth. Mr. Ramsay 

 has arrived at the same conclusion regarding the Australian 

 species : he states that the young cuckoo is at first a little 

 helpless fat creature, but, " as it grows rapidly, it soon fills up 

 the greater part of the nest, and its unfortunate companions, 

 either smothered by its weight, or starved to death through its 

 greediness, are thrown out by their parents." Nevertlieless 

 there is so much evidence, both ancient and recent, that the 

 young Eurojican cuckoo does eject its foster-brothers, that this 

 can hardly be doubted. Now, if it were of great importance 

 to the young cuckoo to receive as much food as possible soon 

 after birth, I can sec no special difficulty in its gradually 

 acrjuiring, during successive generations, the habit (perhaps 

 through mere unintentional restlessness), the strength, and the 

 structure, best fitted for ejecthig its foster-brothers; for those 

 young cuckoos which had such habits and structure would be 

 the best fed and most securely reared. I can sec no more 

 difficulty in this, than in young birds acquiring the instinct and 

 the temporary hard tips to their beaks for breaking through 

 their own shells — or than in young snakes having in their 

 upper jaws, as Owen has remarked, a transitory sharp tooth 

 for cutting through the tough egg-shell. For if each part is 

 liable to individual variations at any age, and the variations 

 tend to be inherited at a corresponding age — propositions 



