110 University of California Publications in Geology [Vol.7 



which tended to reduce the numbers of either group of mam- 

 mals must have reacted also upon the large birds of prey. 



It is not at all improbable that the things which brought 

 about the extinction of Pleistocene mammals were also directly 

 operative in bringing about the extinction of many species of 

 birds. Non-raptorial birds, except where migratory, would re- 

 spond to climatic changes very much as did mammals. Osborn 

 makes suggestions regarding the mammals as follows : 



' ' the Glacial period in North America originated certain new con- 

 ditions of life which directly or indirectly resulted in extinction. 



"These conditions include diminished herds, enforced migrations, the 

 possible overcrowding of certain southerly areas, changed conditions of 

 feeding, disturbance in the period of mating and reproduction, new rela- 

 tions with various enemies, aridity, deforestation ; in short, a host of 

 indirect causes. ' ' 4a 



Disease, in all probability a factor in the extinction of some 

 mammals, may likewise have been the determining influence in 

 the case of certain birds: During the winter of 1908-9 in south- 

 ern California, the bodies of thousands of sea-birds were cast 

 up on the beach within a comparatively short time. Many of 

 these specimens were examined by Dr. F. C. Clark of Los An- 

 geles and by the author. The intestines were found filled with 

 tape-worms. Mildness of the weather coupled with the profound 

 emaciation of the birds indicated that death was not due to 

 violence or sudden cause. While the presence of parasites may 

 not have been the only influence leading to death, it was, in all 

 probability, an important and possibly the determining factor. 



If. as is so variously suggested, the rainfall is now much 

 less than it was during the Pleistocene, the influence upon bird 

 life may have been effective over wide areas through the several 

 factors of food, shelter and nesting sites. Pavo and Meleagris, 

 although not always confined to wooded country, are both forms 

 which might have been strongly influenced by deforestation. 

 The morphnine eagles, with the possible exception of Geranoae- 

 tus, are forest-dwelling birds. The local extinction of these birds 

 in California may have resulted from a thinning-out of the 

 forests. 



43 Osborn H. F., The Age of Mammals (New York, Macmillan, 1910). 



