CALIFORNIA FISH AND GAME 317 



My study of deer has covered all seasons and extended over nearly 

 a score of years and has involved a counted total of over 1000 deer that 

 have actually been watched, for a total of approximately 680 hours, in 

 order to see what their food preferences might be at different seasons 

 of the year and under different conditions. In Yosemite Valley during 

 a single period of observation extending from June 20 to July 2, 1927, 

 a total number of 136 deer were watched for a total of 1218 minutes. 

 By making such a comprehensive study, it is believed that a more 

 accurate and a better general understanding of the food preferences 

 of deer has been obtained than was previously known. It has been my 

 experience that under certain conditions and in certain seasons of the 

 year, mule deer will feed almost exclusively on certain types of foods 

 and plants. If we took into consideration only such observations, a 

 very biased picture would result. 



In order to approach sufficiently close to deer to be able to see what 

 they actually ate, it was necessary that the deer be fairly tame and not 

 fearful of the presence of man. Another important point was that if 

 the free, natural food preferences were to be studied it was necessary 

 that the full complement of food plants be present, because it was soon 

 recognized that deer on range lands or other areas that have been 

 heavily grazed by domestic stock, of necessity ate whatever plants 

 remained and were available at that time. For these and other reasons, 

 it was found expedient to make a special study of the food preferences 

 of deer in our National parks because there grazing by domestic stock 

 has been practically eliminated and because there the full complement 

 of native plants was present. Furthermore my study in Yosemite was 

 made early before deer became overly abundant there. 



Kentucky blue grass, meadow fescue and velvet grass are all 

 present on the floor of Yosemite Valley. This not only gave the 

 observer an opportunity to detect the food preferences of deer as 

 regards native vegetation, but also gave opportunity to ascertain what 

 the reaction of deer might be toward some of our most important 

 introduced range plants and forage grasses. 



In order to insure accuracy, I have verified my findings through 

 the use of 8-power binoculars, which has made it possible for me to be 

 able to see with certainty just what species of plant the deer were 

 feeding on. 



The duration of browsings has been recorded accurately "by the 

 watch, ' ' and is not mere guess work. 



Four methods of recording the findings regarding the food prefer- 

 ences of deer have been utilized. The first was to secure actual photo- 

 graphs of the deer in the act. In order to do this, it was necessary to 

 use a fast, long focus lens, and to be within 25 feet of the deer. For 

 this type of work, I found that a Ross telecentric lens of 17-inch 

 equivalent focal length, with a value of F 5.4, fitted to a 4x5 Graflex 

 camera, gave good results. By means of such apparatus, I have been 

 able to secure graphic and dependable evidence showing what deer eat. 

 In many instances I have not only been able to observe but actually to 

 photograph deer eating certain plants or the foliage of certain trees 



