140 Evolution and Adaptation 



imately infer is, that, although the normal instinct has been 

 changed into another, the race has still been able to remain 

 in existence. The same conclusion applies to the case of 

 MolotJirus bonariensis, cited by Darwin, and is here even more 

 obvious : — 



" Some species of Molothrus, a widely distinct genus of 

 American birds, allied to our starlings, have parasitic habits 

 like those of the cuckoo ; and the species present an interest- 

 ing gradation in the perfection of their instincts. The sexes 

 of MolotJirus badius are stated by an excellent observer, Mr. 

 Hudson, sometimes to live promiscuously together in flocks, 

 and sometimes to pair. They either build a nest of their own, 

 or seize on one belonging to some other bird, occasionally 

 throwing out the nestlings of the stranger. They either lay 

 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 clamoring 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 is known, 

 invariably lays its eggs in the nest of strangers ; but it is 

 remarkable that several together sometimes commence to 

 build an irregular untidy nest of their own, placed in singu- 

 larly 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 

 extraordinary habit of pecking holes in the eggs, whether of 

 their own species or of their foster-parents, which they find 

 in the appropriated nests. They drop also many eggs on the 

 bare ground, which are thus wasted." 



