UNITED STATES DEPARTMENT OF THE INTERIOR, Douglas McKay, Secretari/ 

 FISH AND WILDLIFE SERVICE, John L. Farley, Director 



The investigational work on which this report is based was done 

 while the author was a member of the staff of the Denver Wild- 

 life Research Laboratory of the United States Fish and Wildlife 

 Service. The report was submitted after the author had left the 

 laboratory, and parts of it were condensed and revised by 

 E. R. Kalnibach, (lien director of the laboratory. 



UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1954 



For sale by the Superintendent of Documents, II. S. Government Printing Office 

 Washington 25, D. C. - Price 2.5 cents 



