Volume percentages were estimated directly 
from point contacts. 
Heady and Torell (1949), Lesperance et al. 
(1960), Lusk et al. (1961), Van Dyne and 
Heady (1965), and Galt et al. (1966) used ‘‘mi- 
croscopic point” or “laboratory point’? methods 
to estimate botanical composition of ingesta re- 
trieved from fistulated cattle and sheep. Col- 
lected material is systematically passed under 
a binocular microscope equipped with a cross- 
hair. Species and plant parts under the cross- 
hair are identified and recorded as a hit. Per- 
centage-point data may be converted to weight 
by regression. 
DESCRIPTIVE INDEXES 
In the search for better ways of presenting 
and interpreting results of wildlife food stud- 
ies, various descriptive indexes have been de- 
vised. Some that have received particular at- 
tention equate food availability with consump- 
tion or combine single estimators of diet so as 
to better describe the relative importance of 
food items. 
Glading et al. (1940) were perhaps the first 
to examine food availability-consumption rela- 
tionships. During a period when the diet of the 
California quail consisted almost entirely of 
leaf material, a “desirability coefficient” was 
developed based on the percentage volume in 
the total diet, the percentage occurrence in 
quail stomachs, and the percentage of the spe- 
cies in the plant population: 
Desirability coefficient of a food item = 
Percentage volume Percentage of stomachs 
of this foodin xX in which this 
the total diet food occurred 
Percentage of this species 
in total plant population 
The coefficient was relative and only indicated 
the choice between species available at the time. 
Bellrose and Anderson (1943) obtained a nu- 
merical rating of certain waterfowl food plants 
by dividing the percentage plant use by the 
percentage of plant abundance. An index rat- 
ing of 1.0 for a food plant indicated utilization 
approximately in proportion to its abundance; 
a larger figure indicated a greater food plant 
value; and a smaller figure indicated a lesser 
value. Similar consumption-abundance ratios 
have been used in studies of deer (Hill 1946; 
Chamrad and Box 1968), elk (Harper 1962), 
pocket gophers (Ward and Keith 1962), and 
Sheep and cattle (Van Dyne and Heady 1965). 
Hungerford (1957) combined a measure of 
bod availability with food utilized in a “food 
index”’: 
Food index = 
Percentage utilization x (100—percentage 
availability) 
100 
where percentage utilization equals percentage 
occurrence of various food items in grouse 
droppings and percentage availability equals 
percentage occurrence of food items in plot 
studies on the same brood range. The index is 
based on the assumption that a food item ea- 
gerly sought by grouse but limited in abun- 
dance has a higher relative value than a food 
item commonly available and used with equal 
frequency. Availability is expressed in opposi- 
tion to utilization in order to properly weight 
the index. 
To express numerically the relative impor- 
tance of plants eaten by black-tailed deer, 
Cowan (1945) derived a “consumption index” 
—the mean percentage volume of a plant spe- 
cies in the stomach contents during a seasonal 
period multiplied by the number of months 
represented and totaled over the four seasons. 
The resulting approximate figure was an index 
of the relative bulk contribution of individual 
forage species to annual forage consumption. 
Beck (1952) introduced a ‘‘food-rank index” 
that combined percentage, volume, relative 
weight, and percentage occurrence of food 
items found in turkey crops: 
Index number = Volume of the food item in 
percent X Frequency of the 
food item in percent X Spe- 
cific gravity of the food. 
Later (Beck and Beck 1955) a nutritional 
value was added to the basis formula. 
Baumgartner et al. (1952) developed a “‘vol- 
ume-frequency index” wherein the positioning 
or rank of a food item as indicated by the vol- 
ume index and the rank expressed by the fre- 
quency index were combined as a simple aver- 
age: 
Volume-frequency index = 
Volume rank + Frequency rank 
2 
Both volume and frequency data are equally 
weighted in deriving the index. ; 
Major mule deer food items were graphi- 
cally summarized by Anderson et al. (1965) as 
an “adjusted ratio.” The mean percent volume 
and frequency index of food items were 
equated as a product of the two expressions. 
Volume and frequency estimates were accorded 
equal weights in the ratio product. 
SOME LIMITATIONS OF THE METHOD 
Examination of digestive-tract contents 
provides estimates of the kinds of food taken 
137 
