274 ORIGIN OF SPECIES 



their eggs in the nest thus appropriated, or oddly enough build 

 one for themselves on the top of it. They usually sit on their 

 own eggs and rear their own young; but Mr. Hudson says it 

 is probable that they are occasionally parasitic, for he has 

 seen the young of this species following old birds of a distinct 

 kind and clamouring to be fed by them. The parasitic habits 

 of another species of Molothrus, the M. bonariensis, are much 

 more highly developed than those of the last, but are still far 

 from perfect. This bird, as far as it is known, invariably 

 lays its eggs in the nests of strangers; but it is remarkable 

 that several together sometimes commence to build an irregu- 

 lar untidy nest of their own, placed in singularly ill-adapted 

 situations, as on the leaves of a large thistle. They never, 

 however, as far as Mr. Hudson has ascertained, complete a 

 nest for themselves. They often lay so many eggs — from 

 fifteen to twenty — in the same foster-nest, that few or none 

 can possibly be hatched. They have, moreover, the extraordi- 

 nary habit of pecking holes in the eggs, whether of their own 

 species or of their foster-parents, which they find in the ap- 

 propriated nests. They drop also many eggs on the bare 

 ground, which are thus wasted. A third species, the M. pecoris 

 of North America, has acquired instincts as perfect as those 

 of the cuckoo, for it never lays more than one egg in a foster- 

 nest, so that the young bird is securely reared. Mr. Hudson is 

 a strong disbeliever in evolution, but he appears to have been 

 so much struck by the imperfect instincts of the Molothrus 

 bonariensis that he quotes my words, and asks, "Must we con- 

 sider these habits, not as especially endowed or created in- 

 stincts, but as small consequences of one general law, namely, 

 transition?" 



"Various birds, as has already been remarked, occasionally 

 lay their eggs in the nests of other birds. This habit is not 

 very uncommon with the Gallinaceae, and throws some light 

 on the singular instinct of the ostrich. In this family several 

 hen-birds unite and lay first a few eggs in one nest and then 

 in another ; and these are hatched by the males. This instinct 

 may probably be accounted for by the fact of the hens laying 

 a large number of eggs, but, as with the cuckoo, at intervals 

 of two or three days. The instinct, however, of the American 

 ostrich, as in the case of the Molothrus bonariensis, has not 



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