386 G. O. Batzli et al. 



Habitat Utilization by Caribou 



Migratory caribou move into the Prudhoe Bay region from herds 

 that overwinter in Canada or south of the Brooks Range. The calving 

 areas, located in the northern Foothills, consist of undulating terrain, 

 frequently intersected by small streams. The first snowmelt north of the 

 Brooks Range usually occurs in these areas (Hemming 1971). Snow is 

 gone by the time caribou arrive for calving, and graminoids {Eriophorum 

 spp.) have begun to grow, although green vegetation is very sparse. Calv- 

 ing commences as early as 25 May and usually ends by 20 June (Lent 

 1966, Skoog 1968, White et al. 1981), and the main influx of migratory 

 caribou reaches the Prudhoe Bay region by late June. The resident 

 caribou calve on the Coastal Plain and the Foothills (Cameron and Whit- 

 ten 1979). 



During the summer caribou graze either in small nursery groups of 2 

 to 10 cows with their calves and an occasional yearling, or in groups of 3 

 to 20 bulls and yearlings (White et al. 1975). Early grazing is concen- 

 trated on exposed ridges and pingos that are dominated by dicotyledons. 

 As the snow melts, caribou begin to graze on polygonal terrain and 

 drained lake beds whose vegetation is dominated by graminoids and 

 dwarf willows. Some of the poorly drained centers of low-centered poly- 

 gons and lake beds do not dry until late summer, and the graminoid- 

 dominated vegetation of these areas is utilized then. For most of the sum- 

 mer, caribou prefer to graze on stream banks where the biomass and spe- 

 cies diversity of the forage is high (White et al. 1975). The general sum- 

 mer movement pattern appears to be determined by the phenological 

 progression of vegetation types and associated changes in their nutri- 

 tional status. 



As the season progresses caribou move back from the Coastal Plain 

 to the Foothills, but daily movement patterns are less distinct due to the 

 overriding effects of harassment by mosquitos {Aedes spp.) and warble 

 flies (Oedemagena tarandi). During the warmest periods vegetation asso- 

 ciated with standing water is avoided, presumably because it is prime 

 mosquito habitat. Caribou gain some relief from mosquito harassment 

 by grazing and walking into the prevailing wind. Or they move to the 

 coastal sand dunes where it is cooler and windier than inland. Trail net- 

 works generally join the preferred grazing areas with those areas where 

 they seek relief. Where several trails join at the shores of larger lakes the 

 soil becomes deeply rutted and completely devoid of moss and vascular 

 plants. Once the temperature drops and insect harassment abates, cari- 

 bou graze slowly through the vegetation towards preferred habitat. Little 

 use is made of the trail systems at this time (White et al. 1975). 



In late October groups of caribou gather in herds of over a thou- 



