169 
Table 12 
Seasonal changes in biomass of some vegetation types at Prudhoe Bay (1973). 
Vegetation Number of Dry biomass (g/m?) 
type Date observations Live Dead Total 
Eriophorum angustifolium marsh 7/10/73 3 34.14 6.5 87.1422.1 121.2423 
7/29/73 3 41.4+ 1.6 SMCEE hy) 75.3+ 7.4 
8/12/73 2 18.14 4.4 66.2+ 7.0 84.34 8.9 
9/19/73 3 Wea 228 111.1418.9 118.54+21.5 
Dryas integrifolia heath/ 7/ 8/73 3 35.3+ 4.8 45.5+ 4.4 80.8+ 4.9 
Salix rotundifolia snowbed 7/21/73 3 34.5+ 5.9 UBL 27. 110.8428.1 
9/19/73 &) 21.9411.2 88.8+19.8 110.8+19.5 
Dupontia fisheri brook meadow 7/19/73 3 Wier 87 76.7412.7 147.9+19.0 
8/12/73 3 30.44 3.1 91.9+11.1 122.5+14.1 
9/19/73 a TAL TA 837+ 7.9 91.8+ 9.1 
Carex aquatilis marsh 7/20/73 3 25.94 3:2 55.2+12.6 81.4415.5 
8/ 7/73 3 24.4+ 1.4 39.4+ 5.6 63.9+ 6.7 
9/19/73 3 3.84 2.9 63.1436.4 66.9417.1 
Sand dunes 7/14/73 2 31.4+ 7.6 20.5+12.1 51.907 4.5 
Es 
= 
Qa 
2 6 
3 
€ 
2 
Oo 2 
e 
Jo 
10 20 30 10 20 30 10 20 30 10 20 
June July August September 
Fig. 9. Predicted changes in live biomass 
availability based on data for late July (Table 
72) and primary production rates for Barrow, 
Alaska (Tieszen 1977). , values used to 
calculate eating rate (Fig. 10) and eating time 
(Fig. 11) for the estimation of daily food intake 
(Table 15). A, Eriophorum marsh; O, Dryas 
heath/Salix snowbed,; @, Dupontia brook bank; 
A, Carex marsh. 
food intake for all studies (2.92 g min''). From 
such a high degree of variance, it can be inferred 
that factors regulating food intake were not 
constant from one estimation to the next. 
Changes were made in the experimental 
procedure in the following (1973) field season 
to increase the precision with which food intake 
could be estimated and to investigate some 
factors regulating food intake. Reindeer were 
fasted for 3-4 hr before using them in an intake 
experiment, and the collection period was re- 
duced (e.g., from 20 min in 1972 to 10 min in 
1973). Further, three to five collections were 
made on the one vegetation type, and a 20 min 
grazing period was allowed between collections. 
These experiments indicated that the rate of 
food intake declined at approximately 30% per 
hr during a grazing period. The peak rate of food 
intake increased in a curvilinear fashion with 
available live biomass, as shown in Figure 10a. 
Eating rate was apparently maximized at 6g 
(DM) min! [6/83 = 0.072 g min! kg (BW)"'] 
at and above a live biomass of 70 g (DM) m?. 
It can be calculated that a reindeer confined 
to a small area has the potential to denude a 
range of live biomass 70 g m~? at arate of 11.7 
min m2. This calculation assumes a simplistic 
approach to feeding, for the amount of time 
spent searching is not considered; however, the 
powerful harvesting potential of caribou is 
obvious. 
At the Prudhoe Bay study site, peak live 
biomass was in the range of 30 to 70 g m2 
depending on the harvest date and the 
vegetation type (Fig. 9). Thus, some of the 
variance associated with the 1972 estimates of 
feeding rate (Table 13) could be attributed to 
variations in available biomass at the study sites. 
(b) Calculation of food intake from eating 
rates and time spent eating. During all periods 
free of insect harassment, adult caribou spent 
51% of the day eating (Table 2), and the female- 
yearling-calf group spent 53% of the day eating. 
