untitled

As in body weight measures, flight muscle weights are corrected for body size by

dividing by a standard muscle volume (SMV). Davidson and Evans (1988) used the

formula:

SMV =H(L×W+0.433C^2 )

for shorebirds of the genus Calidris, where His the height of the keel of the sternum,

Lis the length of the keel of the sternum, Wis the width of the raft of the sternum

(one side only), and Cis the distance from the keel to the end of the coracoid.

Direct measures of body weight are feasible with birds and small mammals, but

impractical for large mammals where some other index of body condition and food

reserves must be used. These have been reviewed by Hanks (1981) and Torbit et al.

(1988). Large mammals store fat subcutaneously, in the gut mesentery, around the

kidneys and heart, and in the marrow of long bones. The fat stores are used up in

that order (Mech and DelGiudice 1985). Because of this sequential use no single fat

deposit is a perfect indicator of total body fat. In caribou, for example, a combination

of body mass and a visual index of condition provided the best predictor of fatness

(Gerhart et al. 1996). Particular fat stores are of interest for specific purposes, such

as reproduction (kidney fat) or starvation (bone marrow fat) (Sinclair and Duncan

1972). For these purposes they provide a reasonable guide for managers, total body

fat being less useful.

Ungulates accumulate fat around the kidney and in other places in the body cavity

in anticipation of the demands of reproduction. We saw in Section 4.5.3 how the

fat reserves of mule deer change according to the stage of the reproductive cycle

(Fig. 4.8), the timing of these changes differing between the sexes.

Although there is little relationship between kidney fat and total body fat in some

species (Robbins 1983), others, such as most African ruminants, show a close rela-

tionship (Smith 1970; Hanks 1981). For white-tailed deer the percentage of fat in

the body is related to the kidney fat index (KFI) by:

Percentage fat =6.24 +0.30KFI

(Finger et al. 1981). In mule deer both the weight of kidney fat and the KFI are cor-

related with total body fat (Anderson et al. 1969, 1972, 1990; Torbit et al. 1988).

FOOD AND NUTRITION 55

1.0

0.9

0.8

0.7

0.6

0.5

330

320

310

300

290

280

–4 –3 –2 –1 0 +1 +2 +3

Day in laying cycle

123

Total body fat (g) Flight muscle index

Fig. 4.10Total body fat
() and flight muscle
index () are related to
laying day in the female
gray-backed camaroptera
(a tropical African
warbler). Eggs are laid
on days 1–3. Flight
muscle index is the
ratio of (lean dry flight
muscle weight)/(flight
muscle cord^3 ). The
broken line indicates
estimates. (After Fogden
and Fogden 1979.)

4.9.2Kidney fat
index