Geoscience Reference
In-Depth Information
Table 5.2
Application of Digestion Correction Factors (CF) Used to Estimate
the Biomass Consumed by a Bear
Fecal
Volume
(%)
Percentage of
Dry Matter
Consumed
Volume
ยด
Diet Item
Rank
CF
CF
Rank
Ungulates
31
2
3.0
93.0
54
1
Rodents
4
4
4.0
16.0
9
3
Fish
1
7
40.0
40.0
23
2
Insects
3
5
1.1
3.3
2
6
Coarse vegetation
3
5
0.16
0.5
<1
8
Graminoid foliage
45
1
0.24
10.3
6
4
Forbs
5
3
0.26
1.3
1
7
Roots
5
3
1.0
5.0
3
5
Fleshy fruit
2
6
1.2
2.4
1
7
Seeds
1
7
1.5
1.5
1
7
After table 2 of Hewitt and Robbins (1996). CF = correction factor: grams dry matter ingested per
milliliter residue in feces, determined from feeding trials with captive bears.
al. 1989), the biases associated with the subsequent estimates of biomass con-
sumed will probably be smaller than those based on percentage occurrence or
percentage volume.
Gastrointestinal samples
Contents of alimentary tracts are generally collected only from wild animals
with large populations because they usually involve sacrificing the animal.
Investigators use this approach often on collections during legal hunting and
trapping seasons. These harvests usually span only a short portion of the year,
limiting the application of this technique. For carnivores, harvest samples also
may be biased by foods used as bait. On the other hand, information about the
sex, age, and body condition of the sampled animal and volume of prey con-
sumed is an advantage of this method (table 5.1).
Crop contents of granivores are a very different sample because only lim-
ited digestion has occurred. Often the investigator can separate and identify
the majority of the sample. The volume of each seed type also can be estimated
with a graduated cylinder or by the displacement of a known quantity of water
in a burette (Inglis and Barstow 1960). Seeds and fruit can be identified by
