WIND SPEED 
km hr! /mi hr! 
40/25 
14/15 
IS) 40 45 50 
159 
Air temp.-measured in shade, at 20 cm 
above ground 
Wind speed-km hr! range, at 100 cm 
above ground 
Harassment 
WS l Severe 
se i Moderate 
i None 
55 60 65 OF 
Ambient temperature 
ike) 2ORE 
Fig. 4 Relationship of intensity of insect harassment on caribou with ambient 
temperature and wind speed. 
from a variety of individual behavior responses, 
including tail wagging, ear flicking, head and 
body shaking, twitching, shuddering, leaping, 
and bounding, as described by Thomson (1971, 
1973). 
Mosquitos (Aides spp) became active, and 
the first signs of caribou harassment apparent, as 
shade air temperature increased above 6°C 
under still air conditions. With increasing tem- 
perature, mosquito harassment of caribou be- 
came progressively greater, as did the mosquitos’ 
tolerance for wind. At shade air temperatures of 
over 13°C, usually on warm, sunny days, warble 
flies (Oedemageon tarandi) were observed to be 
active around caribou herds, causing avoidance 
responses typical of severe harassment. This 
relationship between intensity of insect harass- 
ment with ambient temperature and wind 
strength was quantified for the Prudhoe Bay 
area through frequent field recordings (Fig. 4). 
The regularity of the relationship made it possi- 
ble to predict the degree of harassment from 
prevailing weather conditions on any day. 
Unfortunately, the continuous data on air 
temperature and wind speeds at the small Prud- 
hoe Bay meteorological station did not corre- 
spond to the same parameters measured on the 
field, because wind speed near the ground was 
not measured, and because local site variations 
accounted for a considerable variation in tem- 
perature. However, as an approximate guide, if a 
maximum daily temperature of 8.5°C or over 
was recorded, a day of moderate insect harass- 
ment could be predicted. If the maximum was 
13.5°C or over, a day with severe insect harass- 
ment was predicted. The number of days in 
which caribou would experience insect harass- 
ment as predicted from meteorological data is 
listed in Table 4. Also shown in Table 4 are 
estimates of the cumulative duration of harass- 
ment for 1972 and 1973. 
In all years, July is the peak month for 
insect harassment, with 20-25 days mild enough 
for harassment, during approximately half of 
which severe harassment on caribou can be 
expected. For mosquitos, the season extended 
