. Ecological investigations of the tundra biome in the Prudhoe Bay region, Alaska . 25 30 June Fig. 2. Relationship of caribou numbers and intensity of insect harassment at Prudhoe Bay. Caribou numbers were obtained from a census of caribou within binocular range of the road; 1, 2, 3; aerial surveys between coast and Franklin Bluffs. under insect harassment were observed 35 km inland on the moderate heights of the Franklin Bluffs (Gavin, pers. comm.). Population composition sample counts in both years were taken to be representative of the animals present in the Prudhoe Bay area, but not neces
. Ecological investigations of the tundra biome in the Prudhoe Bay region, Alaska . 25 30 June Fig. 2. Relationship of caribou numbers and intensity of insect harassment at Prudhoe Bay. Caribou numbers were obtained from a census of caribou within binocular range of the road; 1, 2, 3; aerial surveys between coast and Franklin Bluffs. under insect harassment were observed 35 km inland on the moderate heights of the Franklin Bluffs (Gavin, pers. comm.). Population composition sample counts in both years were taken to be representative of the animals present in the Prudhoe Bay area, but not necessarily representative of any whole population, such as the Porcupine Herd, the Arctic Herd, or a "resident" Prudhoe Bay popu- lation. For 1972 a calf:female ratio of 67:100 was estimated. This estimate was based on an ob- served ratio of ± calves per 100 females plus yearlings (counts of 941 calves/1,831 fe- males -I- yearlings in 26 herds of size greater than 24 females + yearlings per herd) and an estimat- ed yearling: female ratio of 24:100 (counts of 22 yearlings/90 females). A male:female ratio of 101:100 was based on an observed ratio of 77 males per 100 females plus yearlings (counts of 1,103 male/1,429 females + yearlings). The near- ly equal sex ratio was the result of a large herd of more than 1,000, of which 60% of animals (excluding calves) were males, which were classi- fied as they moved into the area under severe insect harassment in 1972. From the fewer animals present in 1973, three separate counts of at least 120 animals found the calf:female ratio to be 31:100, the yearling:female ratio 25:100, and the male: female ratio 37:100. A comparison of the herd proportions re- corded at Prudhoe Bay with previous estimates of herd proportions is shown in Table 1. The proportion of calves in caribou herds at Prudhoe Bay (16-23% of the herd) is similar to the calf percentage (15-26%) noted for major counts on the Arctic and Porcupine Herds. When the h
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