groups noted had a mean size of 77, with 21 
groups (23%) of more than 100 individuals 
(Table 6). 
Caribou which were not harassed typically 
would be dispersed widely in a loosely coordi- 
nated group, alternating periods of concentrated 
grazing with lying, and often meandering only a 
few km in 24 hours. Caribou under mild insect 
harassment, a situation indicated by frequent 
tail flicking and head shaking, would move 
closer together in an oriented group, walking or 
trotting as they grazed. In a resting period, the 
animals would lie and stand close together; lying 
animals would often jump to a standing position 
and shake or scratch themselves. Under severe 
harassment, large massed herds would be seen 
making long, rapid movements, during which 
individuals would occasionally pause to quickly 
eat, thenrunortrot to rejoin the general move- 
ment. 
Table 6 
Effects of insect harassment on group size. Values 
shown are the number of groups noted in various size 
classes during the study period. 
Group size 1-10 11-50 51-100 101-500 500+ 
No insects 70 42: 11 4 0 
Mild and severe 40 18 13 18 3 
harassment 
The effect of increasing intensity of harass- 
ment on the activity budget was quantified and 
is illustrated in Fig. 5. Grazing and lying times 
declined markedly, and time spent standing en 
masse and in locomotion increased. These 
results parallel earlier findings for wild reindeer 
in Norway (Fig. 5). 
Attempts were made to document the speed 
of movement under different levels of harass- 
ment by relating distance covered to time taken. 
Under insect-free conditions, caribou groups 
averaged 0.53 km hr! over several hours of 
alternating active and rest periods (Table 7). At 
this speed, undisturbed groups would move an 
estimated 14 km per day. 
During insect harassment, the speed of 
movement of caribou depended on the time 
161 
Ti 
ne USA Norway 
Wel (Prudhoe Bay) (Hardangervidda) 
Summer 1972 Summer 1970 
50 
40 Se 
\ Eating 
30 \ mane < 
\ pwalkiog m “Walking 
20 \ =~ Trotting ph 
AS Pe i Lee ey rektion be n 
winegshinas LA unni 
wr Nook a 27S Standing g 
cee Ln 
“\Lying ax a Lying 
poeree Running nal 
None Mild Severe 
Insect Harassment 
None Mild Severe 
Fig. 5. Effect of insect harassment on daily 
activity patterns of caribou at Prudhoe Bay (this 
study) and reindeer at Hardangervidda, Norway 
(Thomson 1971). 
interval chosen. An insect-harassed individual or 
group was observed to run 25-35 km hr! over 
several minutes. Walking, trotting, or running by 
a harassed group averaged 8-16 km hr! over a 
longer interval (for example, during caribou 
movements along the Sagavanirktok River 
towards the coastal area). However, average 
speed of caribou movement was 3.14 km hr’! 
for periods of severe harassment, and 1.36 km 
hr! during mild harassment. The differences 
were significant (Table 7). At these speeds, a 
caribou group harassed for 8 out of 24 hours 
would move a distance of 14 to 42 km, an 
average of 28 km. 
Table 7 
Effects of insect harassment on daily average rate of 
movement. 
Degree of fly harassment 
none mild severe 
Number of groups 13 12 8 
Mean speed (km hr!) 0.53 1.36 3.14 
t-test significance P < 0.05 POM 
P<0.01 
