386 ANNUAL REPORT SMITHSONIAN INSTITUTION, 192 8 



marked zonal characteristics as in the Recent period, so that though 

 the temperature was not oppressively warm it was modern and fairly 

 unifonn at points much farther north than under modern condi- 

 tions. Forms that we consider now as subtropical, in the Miocene 

 and Pliocene ranged north into northern Nebraska, and probably 

 further. We are aware that the present number of species in tropical 

 and subtropical sections of America is much greater than in the 

 Temperate Zone. Ecuador for example, in the geographic limits at 

 present granted to it, has approximately the same area as the State 

 of California. The known bird life of Ecuador at the present time 

 according to Chapman, numbers 1,508 forms, more than for the 

 whole of North America north of Mexico, while that of California 

 at the end of 1924 (the latest published revision of the list) included 

 only 594 species and subspecies. By analogy we may suppose a rich 

 and highly varied bird life for the Miocene and Pliocene periods 

 in North America, a fauna that since has been in part exterminated, 

 and in part restricted to more southern latitudes. Further research 

 may be expected to increase considerably the list of fossil forms 

 known from this section of geologic time. 



With advance into the Pleistocene we come to an age in which the 

 fossil avifauna becomes much better known through more numerous 

 occurrence and greater abundance of specimens. Fifty-one extinct 

 species have thus far been described from our Pleistocene beds, evi- 

 dence of a rich avifauna. There are in addition 108 species of birds 

 still existent whose remains have been identified in Pleistocene de- 

 posits, so that the entire group of this period includes 159 forms of 

 birds, more than half our present list, and a considerable number 

 when we consider the smaller figures yielded by our census in pre- 

 vious ages. 



It may be remarked parenthetically that the more than 50 extinct 

 species that have been described from the Pleistocene are definite 

 indication of what has been said above of the probable abundance of 

 birds at the close of the Pliocene, since these forms undoubtedly had 

 their evolution prior to the Ice Age and w^ere in existence at its 

 beginning. From somewhat meager information I am inclined to 

 regard the close of the Tertiary as the period of greatest diversity 

 and abundance in bird life in the earth's history so far as North 

 America is concerned, and to believe that with the rigors of environ- 

 ment incident to the opening of the Pleistocene, and the even more 

 unfavorable conditions of the historic part of the recent period oc- 

 casioned b}^ the increase of man over the earth, there has been steadv 

 reduction and extermination among birds, a process that will con- 

 tinue in spite of protective regulation until most of the peculiar 

 forms have disappeared and only the more adaptable ones remain. 



