88 BIRDS OF LA PLATA 



on the subject, and will go so far as to suggest what 

 may have been at least one of the many concurrent 

 causes that have produced the parasitic instinct* 

 The apparently transitional nesting-habits of several 

 species, and one remarkable habit of M, bonariensis, 

 seem to me to throw some light on a point bearing 

 intimately on the subject, viz., the loss of the nest- 

 making instinct in this species* 



Habits vary greatly ; were it not so they would 

 never seem so well adapted to the conditions of life 

 as we find them, since the conditions themselves are 

 not unchangeable* Thus it happens that, while a 

 species seems well adapted to its state in its habits, 

 it frequently seems not so well adapted in its rela- 

 tively immutable structure. For example, without 

 going away from the pampas, we find a Tringa with 

 the habits of an upland Plover, a Tyrant-bird (Pz- 

 tangus bellicosus) preying on mice and snakes, another 

 Tyrant-bird (Myiotheretes rufiventris) Plover-like in 

 its habits, and finally a Woodpecker (Colaptes cam- 

 pestris) that seeks its food on the ground like a 

 Starling ; yet in none of these and the list might 

 be greatly lengthened has there been anything like 

 a modification of structure to keep pace with the 

 altered manner of life. But however much the 

 original or generic habits of a species may have 

 become altered the habits of a species being widely 

 different from those of its congeners, also a want of 

 correspondence between structure and habits (the 

 last being always more suited to conditions than the 

 first) being taken as evidence of such alteration 



