162 
(c) Habitat use. Observed movements of 
caribou under insect harassment were not ran- 
dom in the Prudhoe Bay area. With the first 
indication of insect activity, grazing caribou 
would orient into the wind, but would otherwise 
remain grazing on the flat plains which constt- 
tute their major habitat. However, in their graz- 
ing patterns, they would avoid marshy areas and 
the lush vegetation of lake edges where mosqui- 
tos were more troublesome. 
Marsh & lake Plains 
edge veg. veg. veg. 
tO Ce ee Se 
Increasing level of insect activity 
Gravel & sand Sand dune 
(no veg.) 
At an increased level of harassment, groups 
moved more quickly, heading toward areas of 
tundra with the least insect activity. Thus, 
inland groups moved north into the wind toward 
the coast, where the prevailing north wind reach- 
ed its maximum velocity. During this movement, 
caribou frequently moved along river beds and 
on the numerous game trails. In the coastal 
areas, the caribou would find optimum relief by 
lying or standing in the wind-oriented “‘gullies”’ 
of the sand dune area or on the extensive sand 
or gravel bars of the river deltas where lack of 
plant growth was not conducive to mosquitos, 
or even by standing in the open water of the 
rivers and the Arctic Ocean. If harassment was 
not too severe at the coast, the caribou would 
remain there, grazing on the plants of the dry 
sand dune areas. 
Under mild harassment, caribou would often 
remain on the flat plains which constitute the 
major habitat. 
As insect harassment declined, normally in 
association with a reduction in air temperature 
or an increase in wind velocity, herds would 
leave the coastal area and slowly move inland, 
with concentrated grazing and dispersal into 
smaller-sized units, and males and females in 
increasingly segregated groups (Fig. 5). Follow- 
ing several days of freedom from insect harass- 
ment, groups would continue to disperse inland 
out of the study area, but with the return of 
warm, windless weather, the groups would pre- 
dictably coalesce and move rapidly to the coast 
(Fig. 6). 
Influx of migrato: 
caribou in mid to 
Jate June 
f= Insect evoked 
movement 
™ Slow dispersal 
(no harassment) 
Fig. 6. An assessment of the effects of insect 
harassment on observed movements of caribou 
in the Prudhoe Bay area. 
As an alternative to the use of coastal areas 
under fly harassment, males particularly, either 
singly or in groups, would often move onto the 
raised and bare gravel roads and pads of the oil 
development. Individual males could even be 
found standing or lying in the cool shade cast by 
the machinery and equipment around the 
camps. In 1973 higher winds associated with the 
Franklin Bluffs apparently attracted caribou 
seeking insect-relief areas. 
As discussed above, Prudhoe Bay lies in the 
overlap between the summer ranges of two 
major caribou populations which make tradi- 
tional seasonal movements and migrations (Hem- 
ming 1971). However, local summer movements 
and use of the tundra by caribou in the Prudhoe 
Bay area appeared to be dependent on the 
degree of insect harassment and, in insect-free 
periods, on the caribou’s feeding preferences 
within the successional phenology of vegetation 
types (see below). 
Classification of vegetation into 
phyto-sociological units 
Fig. 7 shows diagrammatically the approxi- 
mate pattern of vegetation types in the study 
area; six major terrestrial vegetation types (lle) 
