untitled

1981; Sinclair et al. 1982). However, these are abnormal situations and when

animals are allowed to choose their own diet the relationship holds up. The regres-

sion has been determined for only a few species on natural diets, so more work is

needed in this area. A second potential problem could arise if fecal samples are exposed

to the weather and the nitrogen leached out. For white-tailed deer feces in autumn

the bias is minimal if samples are collected more than 24 days after defecation ( Jenks

et al. 1990).

The relationship between fecal nitrogen and dietary nitrogen can be used to

estimate whether animals are obtaining enough food for maintenance. In African

buffalo the estimate of dietary nitrogen was compared with estimates of dietary

nitrogen from rumen contents (Fig. 4.3). The two are similar.

A similar approach has related fecal nitrogen directly to weight loss. Thus Gates

and Hudson (1981) found that elk lost weight below about 1.6% fecal nitrogen

(Fig. 4.5a) during late winter when there was deep snow (Fig. 4.5b).

FOOD AND NUTRITION 45

10

5

0

ND J FMAJJASOM

Month

Crude protein (%)

Fecal estimate Wet Dry

Diet estimate

Fig. 4.3The proportion
of crude protein in the
diet of African buffalo
declines below the
estimated 5% minimum
requirement in the dry
season. Estimates from
diet selection with 95%
confidence limits (solid
line); estimates from
fecal protein (broken
line). (After Sinclair
1977.)

4.0

3.0

2.0

1.0

0

4.0

3.0

2.0

1.0

0

0 1.0 2.0 3.0 4.0 0 1.0 2.0 3.0 4.0

Fecal nitrogen (%) Fecal nitrogen (%)

Dietary nitrogen (%) Dietary nitrogen (%)

(a) Elk (b) Black-tailed deer

Spring

Summer

Fall

Winter

Fig. 4.4Correlation of
dietary nitrogen with
fecal nitrogen in (a) elk
and (b) black-tailed
deer. Nitrogen increases
with season. Spring
(
); summer (); fall
(); winter (). (After
Leslie and Starkey
1985.)