were required for sampling the diet for most 
botanical constituents. 
Samples must often be acquired from ani- 
mals dying of causes unrelated to the collection 
of data. It is questionable whether such sam- 
ples provide a reasonably unbiased estimate of 
diet. Few data are available on this point; 
however, Leach (1956) reported little differ- 
ence in percentage composition of rumen sam- 
ples taken from winter-killed deer and samples 
collected by shooting. 
Animals vary in the diet they select from 
one location to another, from one season to an- 
other, and even from one year to another 
(Korschgen 1958; Boag 1963). The diet chosen 
may also vary over a period of a few days (Ni- 
chol 1988) and within the same day (Van 
Dyne and Heady 1965). Perhaps less apparent, 
diets may vary among individuals. Individual 
animal selectivity has been demonstrated for 
deer (Duvendeck 1962), mourning doves (Dav- 
ison and Sullivan 1963), sheep (Heady and To- 
rell 1959), and cattle (Van Dyne and Heady 
1965). Hancock (1950) found certain sets of 
monozygotic twins more discriminating in die- 
tary selection than others, whereas both mem- 
bers of a given set of twins showed about the 
same degree of selectivity. Nichol (1938) rec- 
ognized individual preferences among deer, but 
noted that over a long period individual selec- 
tion tended to follow group patterns. 
Differences in diet related to sex (Dalke 
1938; Loveless 1959) and age (Boag 1963; 
Harper et al. 1967) have also been reported. 
Individual variation in food selection could 
have a significant influence on the results of 
studies using limited numbers of experimental 
animals. Feeding trials conducted without ade- 
quate numbers of test animals would appear 
particularly susceptible to bias. 
Preservation 
Sample material is preserved by drying, re- 
frigeration, or immersion in chemical preserv- 
atives. Refrigeration can preserve both the 
color and texture of stored materials. For- 
malin, generally a 4- to 8-percent solution, is 
the most reliable and economical chemical pre- 
servative for stomach, intestine, and crop ma- 
terials. A 70-percent alcohol solution has been 
used for gizzards of small passerine birds. 
Segregation 
Partial segregation of materials recovered 
from digestive tracts is frequently accom- 
plished by rinsing the sample through sieves of 
various mesh sizes, or, if minute particles 
are important, through fine mesh bolting cloth. 
Some have achieved segregation by floating 
or decanting items of different size or spe- 
cific gravity. Arata (1959) used a technique 
based on differential sedimentation of food 
particles of varying sizes and weights. Occa- 
sionally, sample materials can be better exam- 
ined without washing or sieving, for example, 
contents of bird crops or small mammal] cheek 
pouches. 
Final segregation is most often done by 
meticulous sorting and separation, using for- 
ceps. Separation may be accomplished with ei- 
ther wet or dry material, depending on the na- 
ture of the sample, the method of storage, and 
the investigator’s preference. 
The limits to which final segregation is car- 
ried are not well defined, but these are proba- 
bly determined by the composition of the sam- 
ple material, the judgment of the investigator, 
and practicalities of time and economics. The 
volume or weight of unseparated residue may 
be measured, and proportions of constituent 
items may be visually estimated; the residue 
may be proportioned on the basis of identified 
materials, or it may be discarded as unidentifi- 
able. Often only the larger fragments, which 
constitute a small fraction of the original sam- 
ple material, are segregated and eventually 
identified. 
Courtright (1959) criticized estimation of 
ruminant food habits on the basis of only the 
larger and grossly identifiable fragments. He 
found that proportional composition of caribou 
rumen materials caught on 11 different sieve 
sizes (4 to 200 meshes per inch) varied appre- 
ciably in relation to different plant groups. 
Composition of large “identifiable” plant mate- 
rial was not comparable with that of smaller 
particles. Confirming evidence with caribou 
was provided by Bergerud and Russell (1964) 
and Scotter (1966). Dirschl (1962), however, 
presented contrasting results with antelope 
rumen material, finding very little difference in 
the composition of items remaining on three 
mesh sizes (8.5 to 7 meshes per inch). 
Identification 
Accurate identification of ingested food 
items is a difficult yet critically important 
stage in a dietary analysis. Procedures and 
methods used in the identification process are 
discussed in detail elsewhere in these Proceed- 
ings. 
ASSESSMENT AND PRESENTATION OF 
RESULTS 
Various quantitative expressions have been 
used to appraise and describe dietary consump- 
tion. Tabulation of the numbers of each food 
item found, statements of the frequency with 
which each type of food was found to occur, 
and estimates of food mass by weight or vol- 
ume measurement are most commonly used. 
135 
