ez 
There is increasing evidence that harassment 
by flying insects plays a major role in determin- 
ing the movement and activity patterns of 
Rangifer in summer. Harassment leads to an 
increased energy expenditure because of avoid- 
ance movements and a corresponding decrease in 
the time spent grazing. However, whether this 
perturbation can materially affect the amount of 
herbage removed during a summer period has 
not yet been determined. 
Finally, caribou may affect primary produc- 
tion through removal of preferred plant species 
and by trampling. Both natural (e.g., insect 
harassment) and human (e.g., construction of 
barriers) perturbations may cause temporarily 
high stocking rates, resulting in local overgrazing 
and physical damage from trampling. In extreme 
conditions, Overgrazing and trampling may de- 
crease the insulative effects of tundra vegetation, 
which would have long-term visual and topo- 
graphically harmful consequences. 
A recent report considers the effects of 
simulated pipelines on movement patterns 
(Child 1973), while the present report docu- 
ments the normal grazing patterns of caribou in 
the Prudhoe Bay area. 
The objectives of this study were: (1) to 
determine normal activity patterns of the resi- 
dent and transient caribou populations; (2) to 
document the effects of insect harassment on 
activity and movement patterns; (3) to deter- 
mine plant preferences by caribou in relation to 
vegetation phenology and nutrient content, and 
(4) to determine the amount of plant material 
harvested and returned to the ecosystem. 
Methods 
Source of abiotic data 
Daily observations of dry and wet bulb 
temperature (°C), wind speed (km hr''), wind 
direction (degrees true N) and atmospheric pres- 
sure (mmHg) were obtained from climatologic 
data recorded at the Deadhorse and Prudhoe 
Bay airports. These observations were recorded 
on a 2 hourly basis from 0500 to 1800 hr. 
Supplementary field observations of ambient 
temperature and wind speed were made with a 
hand held thermometer and anemometer at 
approximately 1.5 m from the tundra surface. 
Determination of caribou population 
composition 
In 1972 the study area was surveyed mainly 
from the road system (every 1-2 days), and four 
aerial surveys were made. In 1973 composition 
counts were made from the road system each 
2-3 days. 
In road surveys, all animals within binocular 
(10x50) or spotting-scope (25x60) range were 
classified according to age (calf, yearling, and 
adult) and sex. In addition, notes were made on 
group aggregations, locations, and movement 
patterns. 
During periods of high insect harassment, 
caribou numbers, ages, and sex classes were also 
noted from a series of vantage points in the sand 
dunes associated with the Sagavanirktok River. 
Documentation of behavioral and 
activity patterns 
Observations on behavior and recordings of 
activity patterns were made as described for wild 
reindeer in Norway by Gaare et al. (1970) and 
Thomson (1971, 1973). Briefly stated, a suitable 
herd or group of caribou was located and, by 
following unobtrusively, observed for as long as 
possible. At 15 min intervals throughout this 
period, caribou were classified according to the 
number of individuals engaged in each of seven 
categories of activity (eating, lying, standing, 
walking, trotting, running, and other). Between 
these activity counts, observations were made on 
weather data, caribou behavior, movement pat- 
terns, and external disturbances. Similar and 
concurrent observations were made on grazing 
preferences, time spent on different plant com- 
munities, and monitoring of grazing intensity 
(Gaare et al. 1970; Gaare and Skogland 1971). 
Grazing intensity 
Previous workers have defined grazing 
periods in two ways; either the activity associat- 
ed with eating per se (Thomson 1971), or the 
activity associated with searching and eating 
(Gaare and Skogland 1971). In the present 
report, the former activity is described as eating, 
and the latter as grazing. Grazing intensity was 
estimated as the fraction of a grazing period that 
was spent in eating [i.e., grazing intensity = 
eating time/(eating time + searching time)] . 
