BULLETIN 



NUTTALL ORNITHOLOGICAL CLUB. 



vol. vi. October, 1881. No. 4. 



OX SOME OF THE CAUSES AFFECTING THE 

 DECREASE OF BIRDS. 



BY H. \Y. HENSHAW. 



In an extended field experience in Massachusetts and at various 

 points along the Eastern coast, I have often noticed marked 

 changes in the relative abundance of the species of birds of a 

 given locality from summer to summer. A localitv that for 

 several years has furnished a certain species or a summer resi- 

 dent in great numbers will be found after the usual spring mi- 

 gration to be inhabited by comparatively few of that species, 

 although the associate kinds may continue in undiminished force. 

 Or it may be that the reduction will be found to affect several 

 species to a varying degree, involving perhaps birds of very 

 different habits. As my experience in this particular is by no 

 means unique but. on the contrary, as I find, has been shared by 

 every ornithologist whom I have consulted, I have been led 

 to an inquiry as to the probable cause of these seemingly mys- 

 terious fluctuations in the numbers of birds, amounting in some 

 instances to almost the complete extermination of a certain species 

 over a restricted area. 



It is perhaps scarcely necessary to call attention to the fact 

 that the great variation occasionally to be noticed in the number 

 of migrants passing a given point can have comparatively little 

 weight in an estimate of the actual increase or decrease of the 

 several species, the facts concerning migration being too general 



