xviii INTRODUCTION. 



As shown in the succeeding pages, the number of species of Birds as 

 yet ascertained to be found within the Argentine Republic* is about 

 430. We will now take the leading groups of the Neotropical Ornis, 

 one after another, and consider the role they play in the Argentine 

 Avifauna, so as to get some general- ideas as to its peculiarities. 



The subjoined Table contains in the first column the number of Neo- 

 tropical species assigned to each of the different Orders of Birds in 

 the ' Nomenplator Avium Neotropicalium/ In the second column is 

 given the corresponding number of Argentine species of each order 

 according to the present work. The total number of Neotropical species 

 will be seen to be about eight times as many as those of the Argentine 

 Avifauna ; so that where this average is exceeded in the individual orders 

 the particular group may be considered to be over-represented, and 

 where it is not reached to be under-represented in the Argentine Avi- 

 fauna. This is of course a very rough-and-ready mode of calculation, 

 because it assumes that every species has an equal area of distribution, 

 which is not ordinarily the case; but it will serve to give us some 

 general ideas on the subject. We will now proceed to consider the 

 principal groups one after another, and to point out their comparative 

 importance in the Argentine Avifauna. 



The known Argentine Passeres, according to the present work, are 

 229 in number ; those of the Neotropical Region, according to the 

 ' Nomenclator,' are 1976; so that the species of Argentine Passeres, 

 according to the ratio which we have adopted, would be very little short 

 of the average numbers. If, however, we divide the Passeres up into 

 the three suborders of Oscines, Oligomyodse, and Tracheophonse, we 

 shall find that the Oligomyodse are rather in excess of the estimated 

 average, while the species of the two other groups are deficient. This 

 arises mainly from the large number of Tyrannidae belonging to the 

 Argentine Ornis. Not less than 63 species of this group have been 

 already discovered within its limits. Besides Tyrants, other prevailing 

 families of Passeres in the Argentine Avifauna are the Finches (Frin- 

 gillidse) and the Wood-hewers (Dendrocolaptidse), both of which have 

 46 representatives in the Argentine Republic. Both these families are, 

 however, well represented all over the Neotropical Region. But the 

 Tapacolas (Pteroptochidse) and the Plant-cutters (Phytotomidae) are both 



* We have not included within the scope of the present work the territory of Santa 

 Cruz and Tierra del Fuego, which are politically part of the Argentine Republic, but 

 only Northern Patagonia down to the llio Negro. 



