Hexshaw on Causes affecting the Decrease of Birds. 191 



Before advancing an hypothesis to account for the decima- 

 tion in the ranks of species occasionally to be noticed, it may be 

 well to glance at certain factors in the mortality of bird life, 

 natural and other, with a view to ascertaining what part thev 

 play, if any, in the phenomenon. 



As is well known, foxes, skunks, weasels, snakes, and the 

 whole tribe of predatory birds, animals, and reptiles contribute 

 towards the reduction of bird life, and unquestionably in wild 

 sections, where nature reigns supreme, play an important and 

 as usually thought, a beneficent part in preventing the over- 

 production of birds. 



While it is true that the aggregate of birds destroyed by these 

 agents is large, it nowhere, I think, even during the nesting 

 season, the period of greatest danger, amounts to the proportions 

 necessary to account for the decrease noticed. This belief is 

 changed to certainty with respect to the civilized districts, where 

 birds of prey, predatory animals, and even snakes are themselves 

 subject to extermination at the hands of man. 



If the above be true of the nesting season, still less can natural 

 enemies be supposed to affect to any very appreciable extent the 

 ratio of birds at other seasons or in other regions when away 

 from our observation. 



Little appears to be known of the number of diseases among 

 wild birds and the extent to which they prevail. That diseases 

 do actually exist among birds, and to a greater extent than is 

 usually supposed, is, I believe, true, and in a few instances I have 

 myself found dead birds under circumstances that precluded the 

 idea of death from any form of violence.* The almost total 

 lack of evidence upon the diseases of birds is, however, conclu- 

 sive proof of their comparative rarity, f since if serious diseases 

 were common, or anything like epidemics prevailed, we may be 

 sure their presence and effects would make themselves visibly 

 known. 



* Upon this point see Shufeldt in American Naturalist (Vol. XV, Apr. 1881, pp. 

 283-285). The subject is an interesting one and that its fuller investigation would 

 result in developing some valuable facts cannot be doubted. 



t As compared, for instance, with mammals, which are well known to be subject 

 to epidemic diseases that actually depopulate wide districts. Buffalos among large 

 animals, and rabbits among small ones, may be cited in illustration. The latter, par- 

 ticularly, fairly swarm in certain parts of the western Territories, and by their numbers 

 and the consequent damage they inflict upon the farmer would be intolerable nuisances 

 were it not for the occasional epidemics that sweep them off by thousands. 



