254 SPECIAL INSTINCTS, 



build a nest of their own or seize on one belonging to some 

 other bird, occtisionally throwing out the nestlings of the 

 stranger. They either lay their eggs in the nest thus appro- 

 priated, 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 occa- 

 sionally 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 de- 

 veloped than those of the last, but are still far from per- 

 fect. 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 irregular 

 untidy nest of their own, placed in singular 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 extra- 

 ordinary 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. 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 e>gg 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 consider these 

 habits, not as especially endowed or created instincts, 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 Gallinacese, and throws some 

 light on the singular instinct of the ostrich. In this 

 family several hen birds unite and lay first a few eggfs 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 



