378 ANNUAL REPORT SMITHSONIAN INSTITUTION, 192 8 



narily the careful collector of vertebrate fossils finds no bird remains 

 whatever, or at most recovers only a few fragments in the course of a 

 season's explorations in the field. Most of those obtained are secured 

 incidentally in other excavations, the majority of bird bones being 

 small and easily overlooked, or of such form as to offer little promise, 

 so that when only partially exposed they may be disregarded by 

 the searcher for striking specimens. In a few deposits fossilized 

 feathers have been found (see pi. 9) and very rarely fossilized 

 eggs (see pi. 2) are encountered but such finds are unusual and 

 in most cases the sjDecimens are in a highly fragmentary condition. 



Bird remains in the fossil beds below the Pleistocene are charac- 

 teristically fragmentary or broken. Leg and wing bones are those 

 most usually encountered, with occasional parts of vertebrae, pelves, 

 sterna, or ribs. Seldom are more than the merest fragments of 

 skulls secured, and on relatively few occasions have complete skele- 

 tons been found (see pi. 1). 



Birds as individuals exist in enormous numbers, and as there is 

 naturally a constant mortality among them it might be expected 

 that their fossil remains would be abundant. There is no reason to 

 suppose that birds were less common during the Tertiary than now ; 

 in fact there is ground to believe that they may have been more 

 numerous prior to the Recent Period than in the present century. 

 Our present race of civilized man was not then developed to trouble 

 them ; and there is no question but that the rising dominance of man 

 in the last hundred years has had far-reaching effect in reducing 

 the total number of birds, both by man's personal activity in hunting, 

 and by the changes in ecological conditions that have attended his 

 agricultural and commercial developments. Many of our existing 

 species of birds are now able to maintain their living status only 

 through restrictions arranged for their benefit by those far-sighted 

 persons who realize the necessity for conservation in connection with 

 our remaining wild creatures. 



It would seem then that in previous geologic ages there may have 

 been more birds present in North America than exist to-day. That 

 few individuals seem to hare been preserved as fossils is apparently 

 due to the fact that the bones of birds are so light that they are 

 easily destroyed. Most of the limb bones in birds have a hollow 

 center, with comparatively thin walls of dense, rather brittle struc- 

 ture, and when subjected to undue pressure are crushed or broken. 

 Most birds die through capture by some predator, or if overtaken by 

 disease are eaten promptly by some scavenger. As the majority are 

 of small or medium size they are often entirely consumed, and their 

 Ijones comminuted or destroyed by the strong digestion of the creature 

 that has found or captured them. 



