110 University of California Publications in Geology (Vou.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.’ 43 
Disease, in all probability a factor in the extinction of some 
mammals, may likewise have been the determining influence in 
the ease 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 Geranoaé- 
tus, ave 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, Maemillan, 1910). 
