DETERMINING THE KILL FACTOR FOR BLACKTAIL DEER 

 IN THE SOUTHWEST 



By Aldo Leopold 



Assistant District Forester, U . S. Forest Service 



In the regulation of cattle grazing on the National Forests, when 

 there is no opportunity actually to count the cattle, the Forest Service 

 makes use of a formula to determine the probable number of grown 

 animals on the range. This formula is based on one or both of two 

 factors known as the "calf-tally factor" and the "steer factor," re- 

 spectively. The formula is as follows : The number of groivn cattle 

 is equal to three times the number of calves branded annually, or six 

 times the number of steers sold annually. ' 



The formula is, of course, derived empirically, and the two factors 

 used hold good only under normal conditions. For an especially good 

 breeding range, or after an abnormally close gathering, or where 

 predatory animals destructive to young stock are absent, or where 

 heifers have been sold, the factors must be lowered. Under the reverse 

 conditions, the factors must be raised. Nevertheless the formula, 

 when used with good judgment, has been found workable and accurate 

 enough to be accepted by both stockmen and Forest Service officers 

 as a satisfactory l)asis for allotting range privileges, paying grazing 

 fees, and removing natural increase from the range. 



Broadly speaking, the steer factor is an index of the productive 

 capacity of the herd. In a previous article,^ an argument was advanced, 

 and I think established, to the eti'cct that the first step toward efficient 

 management of big game on the National Forests must consist of a 

 quantitative regulation of the annual kill. In other words, the kill 

 must be limited to the productive capacity of the herd. If the steer 

 factor is a satisfactory index to the productive capacity of a herd of 

 cattle, why may not a similar factor — a kill factor — be determined to 

 serve as an index to tlu- ])ro(luctive capacity of a herd of game? 



This question has been asked and debated for four years by the men 

 in charge of game management in the Southwestern District, and steps 



' "Forestry and Game Conservation," Journal of Fori;strv, .'Xpril. I'.MS. 



131 



