171 
Table 14 
Comparison of grazing intensity (tSE) and the predicted time spent eating by unharassed 
caribou groups and reindeer. 
Number of 
Group observation 
Caribou males 22 
Caribou, lactating females 22 
Caribou, nonlactating females 4 
and yearlings 
Caribou, calves (3-4 wk of age) = 
Esophageal fistulated reindeer, 19 
nonlactating females 
Predicted daily 
Grazing intensity eating intensity 
(%) (%) (min) 
60.4+4.3 46(40-50) 662 
79.5+2.3 57(53-60) 821 
67.5+6.0 49(45-53) 706 
— 24 346 
68.2+3.9 = = 
Grazing intensity = (eating time/eating time + searching time) x 100. 
Values in parentheses are the likely range for testing this model. 
*Based on an observed value of 52.8% for the eating intensity of females (Table 2) 
and the assumption that all cohorts spend approximately 66-67% of the day grazing (see 
text). 
availability was taken from previous studies on 
sheep (Allden and Whittaker 1970; Young and 
Corbett 1972) and adapted to the Prudhoe Bay 
site (Fig. 10b). It was assumed that (a) a mean 
live biomass of 45 g m? was available to the 
caribou in June, and (b) the relationship be- 
tween percent of day spent eating and live 
biomass was similar for the three cohorts. Thus, 
three parallel lines were available for the calcula- 
tion of the percent of day spent eating as the 
live biomass altered seasonally (Fig. 10b). 
The simplistic expression for calculation of 
food intake is given as 
food intake = eating rate x eating time. 
From the above discussion, it is clear that both 
factors on the right side of the expression are 
proportional to available biomass, and the rela- 
tionship between daily food intake as a function 
of live plant biomass is shown in Fig. 11. 
In the present study, the mean seasonal 
change in biomass was estimated from the trends 
in Fig. 9 in five 10-day intervals commencing 20 
June. At the extremes during late June to early 
July, the main vegetation type consumed was 
the Dryas heath/snowbed type of biomass 25 
g m~ (Fig. 9), while in late July to early August 
the Dupontia brook bank community of 
biomass 35 to 50 g m-2 was preferred. In the 
main, caribou were assumed to graze the 
Eriophorum marsh, with a live biomass in the 
range 25-45 g m2. 
= 200 
™ 
2 | 
© 150 eae © aul 
= oo A AA —A—4—A 2 
S ees °3 
= [oe y, 
x oa 
s VA 
& ° 
S250 
je) 
9 
Ww 
ANS 
B 
Q ) 20 40 60 80 100 
Live Biomass (g DM m-2) 
Fig. 11. Theoretical relationships between daily 
food intake and availability of live biomass for 
lactating females (1), adult males (2), and non- 
lactating females (3). The relationships were 
calculated as the product of relationships shown 
in Figs. 10a and 10b. 
Summaries of expected biomass of live mate- 
rial, predicted mean daily food intake, and 
energy intake are shown in Table 15. For pur- 
poses of calculation, body weights of the adult 
cohorts—males, non-lactating females, and 
lactating females—were assumed to be respec- 
tively 115, 83, and 83 kg. 
