132 JOURNAL OF FORESTRY 



are now under way to determine the kill factor for blacktail deer under 

 southwestern conditions. The purpose of this article is to outline and 

 discuss the methods which are being used. 



in the tirst place, it may not come amiss accurately to define the term 

 "kill factor." The kill factor is the ratio existing between the number 

 of breeding animals on the range and the number that may annually 

 be killed without decreasing the breeding stock. In short, it is the 

 ratio between the game census and the annual kill. It has a different 

 value for each species and each locality. It automatically takes into 

 account all normal factors bearing on the productive capacity of the 

 herd, such as secret, illegal killing, predatory animals, cripples, starva- 

 tion, and disease. On account of the polygamous nature of most big 

 game, the consequent destructiveness of killing females, and the now 

 almost universal prevalence of "buck laws," the kill factor is premised 

 on an annual kill of males only. The kill factor is, of course, roughly 

 analagous to the annual increment as that term is used in connection 

 with the forester's regulation of cut. 



In the second place, it is to be kept in mind that the kill factor not 

 only should serve to determine the allowable annual kill from a given 

 herd on which we have a census but, likewise, should serve to give 

 us a census of a herd that has successfully sustained a known annual 

 kill. In other words, census times kill factor equals annual kill, and 

 annual kill divided by kill factor equals census. The steer factor also 

 is used in this way. 



So much for the wherefore of the kill factor, its definition, and its 

 mathematical relations. Now we come to the important point : How 

 is it to be determined ? For years past each forest ranger has been 

 required to submit annually an estimate of the big game killed on his 

 district. In this vast accumulation of figures, assuming that the 

 breeding herds have held their own, we should have some very valuable 

 figures on the actual annual kill. But these figures are mere estimates 

 made by a large and changing personnel. Presumably, the errors they 

 contain should be compensating errors. An examination of the records 

 in District 3, however, indicates that they are mostly too rough to be 

 usable. During recent years, some of the districts also have been 

 accumulating data on a game census. Some of these figures, for 

 reasons not relevant here, are unreliable, but others are comparatively 

 accurate. Where these good figures on a census exist, and where the 

 herds liave held their own. it ought to be possible to take the more 



