154 
At the end of a collection period, the appa- 
ratus was taken from the animal, and saliva was 
forced from the forage sample by squeezing. Wet 
weights of forage and saliva samples were deter- 
mined, and the forage was subdivided for deter- 
minations of plant species composition, dry 
matter content, and chemical composition. 
Identification of plant material in rumen and 
esophageal egesta samples 
Rumen and esophageal egesta samples were 
preserved in 80% ethanol. Since chlorophyll is 
removed from plant parts by alcohol, identifica- 
tions were made within 2 days of sampling to 
determine live and dead plant parts. Samples in 
the preservative were added to an enamel tray 
(25x40 cm), and 200 point identifications were 
made with a binocular (x10) as described by 
Galt et al. (1969); Gaare et al. (1970); Gaare and 
Skogland (1971). 
For comparison with samples of rumen con- 
tents and esophageal egesta, the plant species 
composition of communities on which the ani- 
mals were grazing was also determined (see 
Description of vegetation, above). 
Estimation of plant biomass and primary 
production 
Biomass estimates were made by clipping all 
vegetation above the moss layer in 30x30 cm 
plots. Clipped vegetation was sorted into green 
(live) and dead material, weighed, and dried at 
5021G: 
Above-ground vascular production was esti- 
mated through the season from changes in 
biomass; total yearly above-ground production 
was estimated, assuming that peak green biomass 
represents total annual production (Tieszen 
1972). 
Chemical analyses 
Dry matter content of vegetation, rumen 
samples, and esophageal egesta samples were 
determined by drying to constant weight in a 
forced air oven at 40-55° C. 
Estimates of cell contents, hemicellulose, 
and ligno-cellulose in vegetation were made 
using the acid detergent/neutral detergent tech- 
nique of Goering and Van Soest (1970). Lignin 
content was determined on the acid detergent 
residue using concentrated H,SO, (Goering and 
Van Soest 1970). 
Estimation of /n vitro digestibility 
The two stage, micro-digestion, /n vitro tech- 
nique of Tilley and Terry (1963) was used to 
determine the approximate digestibility of 
forage samples. Rumen liquor for the first stage 
of the digestibility was obtained from tranquil- 
ized caribou and the rumen fistulated reindeer. 
Strained liquor samples were incubated anaero- 
bically with buffer and 0.5 g samples of forage. 
The second stage digestion with a pepsin-HCl 
solution was carried out as recommended by 
Tilley and Terry. 
Results 
Caribou numbers and populations composition 
at Prudhoe Bay 
The location of the study area at Prudhoe 
Bay relative to the river systems is shown in 
Fig. 1. The 300 ft (91.5 m) contour indicates 
the most northern limit of the foothills of the 
Brooks Range. The heavily shaded area repre- 
sents that area which could be surveyed from 
the road system at Prudhoe Bay. A map pre- 
pared from aerial photographs of this road net- 
work and gravel pads is shown in Fig. 1a, with 
individual study sites marked on the map. 
5 | 1 
/5f® 150° 143? 148° 197° 
Fig. 1. Location of study area relative to the 
drainage system of the Kuparuk and Saga- 
vanirktok Rivers at Prudhoe Bay. 
