In addition to microtine rodents, arctic 
ground squirrels (Cite//us undulatus) reside in 
the area. Arctic fox (A/opex lagopus) roam as 
predators of these small mammals (Underwood, 
this volume). Populations of caribou (Rangifer 
tarandus granti) graze the area during the sum- 
mer (White et al., this volume). About a dozen 
other species of mammals, including the grizzly 
bear (Ursus horribilis) and wolf (Canis lupus), 
have been occasionally reported in the general 
vicinity of Prudhoe Bay (Bee and Hall 1956). 
Live trapping: Capture-mark-recapture 
To assess numbers and demographic features 
of the microtine rodent populations, live trap- 
ping grids for small mammals were established in 
early June 1971 at locations shown in Fig. 1. 
The primary study areas were near the intensive 
IBP sites on the west side of the road leading NE 
to the Putuligayuk River. Live trap grid P was 
set at about 70°16’N, 148°34’W in a habitat 
with low relief polygons and tussocks. Live trap 
grid O was set about 1 km SW of grid P in a 
flatter habitat of low relief tussocks. In June 
1972 a third live trap grid S was established 
across the road (1 km NE of grid P) on a low 
pingo and the surrounding, very low relief 
tussocks. 
The live trapping, mark, and recapture ap- 
proach was similar at all locations. Live trapping 
grids consisted of 100 trap stations (10 rows x10 
rows) at 5 to 6 m intervals (total area = 0.25 ha). 
One large, Sherman live trap and a nest can with 
cotton bedding and oats was placed at each 
station. During each trapping period of 2 to 5 
days, traps were checked in the morning and 
afternoon. In some instances traps were checked 
more frequently (as often as every 4 hours) to 
reduce or eliminate trap mortality. Traps were 
locked open during the interval of 2 or 4 weeks 
between trapping periods. At first capture in 
each period, animals were tagged on the right ear 
with a fingerling tag, weighed with a Pesola 
spring scale, and examined for reproductive 
status before release at the site of capture. 
Females with a perforate vagina or vaginal plug, 
open pubic symphysis, and/or enlarged teats 
(nipple more than 1 mm in diameter) were 
considered in breeding conditions, as were males 
with scrotal testes (Krebs 1964; Batzli and 
Pitelka 1971). Trapping usually was continued 
137 
in a period until all tagged animals were re- 
captured. 
Temporary live and snap trapping 
In addition to maintaining these permanent 
live trap grids, attempts were made to capture 
microtine rodents at other locations by tempo- 
rary snap trapping and live trapping. In June 
1971, snap trapping grids were set out at two 
sites: (1) on the area later established as live trap 
grid S; and (2) across the main road from the 
intensive sites to the SW of the live trap grids. 
These snap trap grids consisted of 100 stations 
(10 rows x 10 rows) at 10 m intervals with two 
Victor-type snap mousetraps per station. The 
closed traps were prebaited with peanut butter 3 
days prior to trapping. They were checked at 
least twice per day for 5 days during the trap- 
ping period. These same two sites were trapped 
again in August 1971, but with temporary live 
traplines consisting of two parallel rows of 25 
stations at 5 m intervals and one large Sherman 
live trap per station. Rows were about 25 m 
apart, and traps were checked twice per day for 
5 days. In July 1971 two new areas about 10 
km NW of the Putuligayuk River, just NE of 
Frontier Camp and just N of Western Pad, were 
explored and trapped with the same type of 
temporary live traplines. In August 1972 at- 
tempts were made to capture lemmings near pad 
F with temporary live traps. 
Estimates of density 
Estimates of density were calculated from 
the number of animals captured during a trap- 
ping period and the effective trapping area. The 
effective trapping area was calculated for each 
“sex-age’’ group of lemmings by adding a bound- 
ary strip around the actual 0.25 ha grid area. 
The size of the boundary strip was based on 
previous studies of collared lemming (Dicro- 
stonyx groenlandicus) movements and range by 
Brooks and Banks (1971). It was assumed, but 
remains to be confirmed, that the range lengths 
found for different sexes and ages of collared 
lemming at Churchill, Man., Canada (Brooks and 
Banks 1971) apply to the lemmings at Prudhoe 
Bay as well. Thus, for each ‘‘sex-age’’ group a 
boundary strip of approximately half the aver- 
age range length was added to the original grid 
size to give the effective trapping areas shown 
under Table 3. 
