U. S. Department of the Interior

Bureau of Land Management

BLM Alaska Open File Report 125

BLM/AK/ST-11/004+6610+F0000

July 2011

Caribou Use of Narrow Land Corridors around 

Teshekpuk Lake, Alaska

Dave Yokel, Alex Prichard, Geoff Carroll, Lincoln Parrett, Brian Person, 

and Caryn Rea

BLM

Alaska

Teshekpuk

Lake
The BLM Mission

The Bureau of Land Management sustains the health, diversity, and productivity of the public lands for the 

use and enjoyment of present and future generations.

Cover Illustration

Movements of caribou outfitted with GPS collars around Teshekpuk Lake in 2004 and 2005 (see Figure 6, 

page 10). 

Authors

Dave Yokel is a wildlife biologist with the BLM’s Arctic Field Office in Fairbanks. Alex Prichard is a senior 

scientist with ABR, Inc. of Fairbanks, Alaska. Geoff Carroll and Lincoln Parrett are wildlife biologists with 

the Alaska Department of Fish and Game in Barrow and Fairbanks, Alaska, respectively. Brian Person is 

a wildlife biologist with the North Slope Borough in Barrow, Alaska. Caryn Rea is a senior staff biologist 

with ConocoPhillips Alaska Inc. in Anchorage, Alaska.

Disclaimer

The mention of trade names or commercial products in this report does not constitute endorsement or 

recommendation for use by the federal government.

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A bibliography of scientific reports is online at www.blm.gov/ak. 
Caribou Use of Narrow Land Corridors 

around Teshekpuk Lake, Alaska 

Dave Yokel, Alex Prichard, Geoff Carroll,

Lincoln Parrett, Brian Person, and Caryn Rea

BLM-Alaska Open File Report 125

July 2011

U. S. Department of the Interior

Bureau of Land Management
i

Abstract

We used 17 years of satellite- and GPS-collar location data to investigate how 2 narrow land areas constricted movement of the Teshekpuk 

Caribou Herd around Teshekpuk Lake in northern Alaska. In the future, 

the oil industry may build pipelines in one or both of these constricted 

zones, identified as the Smith Area (northwest of the lake) and the Kogru 

Area (east of the lake). To mitigate impacts of pipelines on caribou movements, we need pre-development movement data to understand how caribou 

use these corridors in the absence of pipelines. Caribou used the areas 

most extensively during summer, especially in early July, when at least 

73% of collared caribou accessed the area north of the lake through one or 

both narrow corridors. The proportion of collared caribou was consistently 

higher in the Kogru Area than in the Smith Area. A slightly higher proportion of caribou moved north across the Smith Area than moved south, 

while a higher proportion moved south across the Kogru Area than moved 

north. This resulted in a tendency for a clockwise movement around the 

lake. Weather patterns and caribou behavior during mosquito season may 

explain this pattern. The proportion of satellite-collared caribou moving 

across the constricted zones varied widely among years—from 14% to 

83% for the Smith Area and from 17% to 77% for the Kogru Area. Caribou 

movements were slowest in June and most rapid in July, when caribou 

movements were also more rapid in the constricted zones than on either 

side of them. Although GPS-collar data provide more extensive and accurate information than satellite-collar data, some of the trends observed 

from GPS-collar data in this study were relatively weak due to the small 

sample size. The BLM needs to stay engaged in the collection of those data 

and require an updated analysis before approving any future pipelines 

through one or both constricted zones.

Acknowledgements

In addition to the authors, many biologists, pilots, and high school 

students have helped with annual collaring operations over the 17 years of 

data collection. Attempting to list all of them here would inevitably result 

in some omissions. Likewise, many additional people from the authors’ 

agencies or corporations have contributed to project planning and implementation, funding, data administration and analysis, and publications. 

We express our gratitude to all.
Contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i 

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Satellite Collars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

GPS Collars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Weather Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Satellite Collars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

GPS Collars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Management Implications....................................................15

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figures

Figure 1. Map of the study area and 2 constricted zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 2. Map showing locations of 102 caribou outfitted with satellite collars . . . . . . . . . . . . 5

Figure 3. Mean proportion of satellite-collared caribou in constricted zones or north of 

Teshekpuk Lake, 1997–2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 4. Mean proportion of satellite-collared caribou crossing each constricted zone 

by direction of travel and total, 1997–2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 5. Mean proportion of satellite-collared caribou crossing each of the 2 constricted 

zones during July, 1991–2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 6. Map showing locations and movements of 10 GPS-collared caribou around 

the 2 constricted zones, July 2004–June 2005 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 7. Map showing locations and movements of 12 GPS-collared caribou around 

the 2 constricted zones, July 2006–June 2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 8. Temperatures and wind speeds at Barrow, Lonely, and Marty’s Strip, 

Alaska, during July 2004 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Figure 9. Movement rates of 22 GPS-collared caribou in 4 geographic areas by 

5 movement categories in July 2004 and July 2006 . . . . . . . . . . . . . . . . . . . . . . . . . 14

Tables

Table 1. Number of times GPS-collared caribou entered constricted zones by year, 

month, and movement direction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Table 2. Number of GPS-collared caribou entering the constricted zones, 2004–2007 . . . . . 8

Table 3. Movement rates of GPS-collared caribou north of Teshekpuk Lake and in 

constricted zones, 2004–2007 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Table 4. Movement rates of GPS-collared caribou that crossed constricted zones 

and duration of crossing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

iii
BLM Open File Report 125 • July 2011 1

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

Introduction

Caribou (Rangifer tarandus) of the 

Teshekpuk Caribou Herd (TCH) calve near 

Teshekpuk Lake in northern Alaska (Carroll

et al. 2005; Parrett 2007; Person et al. 2007). 

To the north of Teshekpuk Lake is an isthmus approximately 40 mi (60 km) long and 

20 mi (30 km) wide between the lake and 

the Beaufort Sea. On both the eastern and 

western sides of the lake, narrow corridors 

of land extend from the lake to the sea coast. 

These corridors create constricted zones 

through which caribou must pass to access 

the area north of Teshekpuk Lake (Figure 

1). On the western side of Teshekpuk Lake 

is a constricted zone about 7 mi (11 km) wide 

between the lake and Smith Bay (hereafter 

designated as the Smith Area). On the eastern 

side of Teshekpuk Lake is a constricted zone 

about 8 mi (13 km) wide between the lake 

and the Kogru River (hereafter designated 

as the Kogru Area). On warm, calm days in 

late June, July, and early August, mosquito 

harassment of TCH caribou can be severe. 

A large proportion of the TCH use the area 

north of Teshekpuk Lake for mosquito relief 

during these periods (Prichard and Murphy 

2004; Parrett 2007; Person et al. 2007), when 

the proximity of the Beaufort Sea and Teshekpuk Lake generally keeps temperatures lower 

and wind speeds higher than in areas farther 

inland (Parrett 2007). Thus, caribou heavily 

use the constricted zones on either side of 

Teshekpuk Lake during midsummer as they 

travel to and from mosquito-relief habitat 

north of the lake (Person et al. 2007).

As early as 2018, the Bureau of Land Management (BLM) may hold oil and gas lease 

sales for the area north of Teshekpuk Lake 

(USDOI BLM 2008). Any subsequent development would include pipelines transporting 

products to market through the constricted 

zones. Pipelines have the potential to impede 

or deflect caribou movements (Lawhead et 

al. 2006). If caribou were unable to achieve 

an optimal spatial and temporal pattern of 

insect avoidance, the negative impact on 

caribou energy balance could lower the ability 

of females to bear calves the following year 

(Murphy and Lawhead 2000). Baseline data 

on constricted zone use by caribou will be 

crucial for mitigating impacts through effective planning for potential oil development 

and testing the efficacy of mitigations following development. 

Methods

Satellite Collars

We analyzed existing telemetry data to 

better understand caribou distributions and 

movements in the vicinity of Teshekpuk 

Lake. Over a 17-year period (1990–2007), we 

outfitted a total of 102 caribou (81 females, 

21 males) with satellite collars (Platform 

Transmitter Terminals; Service ARGOS 1988) 

as part of a cooperative program between 

the BLM, the North Slope Borough (NSB), 

and the Alaska Department of Fish and 

Game (Philo et al. 1993; Person et al. 2007). 

Data from TCH caribou fitted with satellite 

collars were obtained for the period July 

1990–August 2007. Collars on marked caribou 

transmitted signals for a mean duration of 

526 days per collar. A few caribou moved 

between herds after collaring; 4 female TCH 

animals joined the Central Arctic herd and 5 

TCH animals, 1 male and 4 females, joined 

the Western Arctic herd (Person et al. 2007). 

We assumed a caribou to have switched 

herds if it was in the calving area of another 

herd during a subsequent calving season. We 

included only locations from TCH caribou in 

this analysis. 

Polar-orbiting satellites received TCH 

collar locations from satellite collars and 

transmitted them through Command and 

Acquisition Stations to data-processing 

centers operated by Service Argos (Landover, 

Maryland), which forwarded them monthly 

to the North Slope Borough for data 

archiving. In 1990–1991, we programmed 

TCH satellite transmitters to transmit 

6 h/day for a month after deployment, then 

6 h/2 days for 11 months. During 1991–2002, 

we programmed most collars to transmit 

6 h/2 days throughout the year. After 2002, 

we had most collars programmed to transmit 

once every 6 days in winter and every other 

day during summer. Most of the TCH collars 

deployed in 2000 malfunctioned and transmitted data only sporadically. 
2

BLM Open File Report 125 • July 2011

Figure 1. The study area, showing the locations of the 2 constricted zones around Teshekpuk Lake, Alaska, and 2 wea

temperature and wind speed during summer 2004.
BLM Open File Report 125 • July 2011 3

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

Although satellite-telemetry locations 

are considered accurate to within 0.3–0.6 

mi (0.5–1 km) of the true locations (Service 

Argos 1988), the data also require screening to remove spurious locations. Using the 

method of Prichard and Murphy (2004), we 

screened data to remove 1) duplicate locations, 

2) locations obtained before collaring or after 

mortality or collar removal occurred, and 

3) locations for which the Argos-designated 

location-quality score (NQ) had a score of 

zero or “B”, indicating unreliability (Service 

Argos 1988). NQ scores of “A” tend to be more 

accurate than scores of zero (Hays et al. 2001; 

Vincent et al. 2002), so they were retained. 

We removed locations that obviously were 

inaccurate because they were far offshore 

or far from other locations. We applied a 

distance/rate/angle (DRA) filter to remove 

locations that appeared to be incorrect based 

on the distance and rate of travel between 

subsequent points and the angle formed by 

3 consecutive points. Any 3 locations with 

an intervening angle of <20 degrees where 

both “legs” had speeds greater than 6 mi/h 

(10 km/h) were assumed to be inaccurate and 

were removed, unless the distance of either 

leg was less than 0.6 mi (1 km) (Prichard and 

Murphy 2004). If the distance of any leg was 

<0.6 mi (<1 km), then we did not remove the 

location because it was close to a previous or 

subsequent location and, therefore, likely to 

be accurate. 

We selected the location with the highest 

NQ score during each duty cycle, defined 

as a period of transmission of location data 

(typically 6 h/2 days), for further analyses. If 

multiple records in a duty cycle were tied for 

the highest NQ score, we chose the location 

with both the highest NQ score and the lowest value of epsilon (ε; Keating 1994). Epsilon 

is similar to our DRA filter, because it is 

calculated using 3 successive locations and 

is a measure of the distance between locations, the angle formed by the 3 locations, 

and the similarity of length between the 

2 legs (Keating 1994). 

Because satellite-collar data have low 

spatial accuracy and temporal resolution 

(relative to GPS collars, see below), we did 

not consider these data adequate for determining specific caribou movement paths 

used to traverse the constricted zones or 

movement rates between locations. Such 

data, however, do provide accurate information on timing of use of the areas as well 

as movements through these zones. In the 

case of our dataset, they also provide a large 

enough sample size to account for variation 

among years. To determine the proportion of 

caribou using the constricted zones and the 

area north of Teshekpuk Lake, we analyzed 

caribou point locations and determined which 

caribou movements crossed each constricted 

zone, as depicted in Figure 1, and recorded 

the direction of movement (north-to-south or 

south-to-north). We determined the proportion of collared caribou using the constricted 

zones during each of 24 half-month time 

periods (e.g., 1–15 January, 16–31 January, 

1–15 February, etc.). Because we captured 

and collared most caribou in the vicinity of 

Teshekpuk Lake, we screened out locations 

within 30 days of capture. In this way, we 

eliminated potential bias that could have 

occurred from a preponderance of movement 

rates for caribou close to the sites where 

we chose to capture and collar them. We 

included only those animals that had 6 or 

more locations within each time period to 

ensure that we had a good record of an 

animal’s movement for that period (Person 

et al. 2007).

GPS Collars

In recent years (2004 and 2006) we fitted 

some TCH caribou with geospatial positioning system (GPS) collars, which provide 

more frequent locations (a location every 2 

or 3 hours throughout the entire year) with 

increased accuracy.

We fitted 10 female caribou from the TCH 

with GPS collars in July 2004 (collar model: 

Telonics [Mesa, AZ] TGW-3680 GEN 3; storeon-board configuration with Argos satellite 

uplink). We recaptured these animals and 

removed the collars in July 2005. All 10 

caribou survived for the entire period; 7 had 

calves in 2005, 2 did not, and 1 had a calf 

that died soon after birth. The GPS collars 

recorded locations every 3 hours.

We fitted 12 female caribou from the TCH 

with GPS collars (also Telonics model TGW3680) during 8–10 July 2006. The sample of 
4

 

BLM Open File Report 125 • July 2011

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

collared female caribou comprised 7 adults 

aged 3 years or more, 3 two-year-olds, and 2 

yearlings. These collars were programmed to 

record locations every 2 hours. Two caribou 

died in spring 2007 (1 in March and 1 in 

May), and we retrieved the other 10 collars 

in late June 2007. 

We analyzed the movements of these 22 

female caribou to determine how often caribou 

traveled through the 2 constricted zones on 

either side of Teshekpuk Lake. As with the 

satellite data, we screened the GPS data to 

remove any locations obtained before collaring or after collars were removed or mortality 

occurred, as well as any locations that obviously were incorrect because they were far 

offshore or far from previous and subsequent 

locations. We also used a distance/rate/angle 

filter, described above, to screen out erroneous locations. The high spatial and temporal 

resolution of these data provided relatively 

accurate estimates of the movement paths of 

caribou using the corridors. 

We calculated movement rates by dividing 

the straight-line distance between consecutive 

locations by the time difference between locations. To calculate the average movement rate 

for caribou traveling through a constricted 

zone, we calculated the average movement 

rate of all caribou segments while the caribou 

was in the constricted zone. Because calculations of movement rates are sensitive to the 

duration of time between locations (i.e., the fix 

interval), we increased movement rates estimated from locations with a 3-h fix interval 

by 5.6% to make them approximately comparable to movement rates calculated from 

locations with a 2-h fix interval. We based 

this adjustment on an analysis of the change 

in movement rate estimates with fix interval 

conducted with this data set (Prichard 2008).

We compared movement rates during July 

with a 2-factor ANOVA model with year (2004 

or 2006) and area (Kogru Area, Smith Area, 

or North of Teshekpuk Lake) as factors and 

natural logarithm of movement rate as the 

dependent variable. Only movement rates 2 

or 3 h apart were included in the analysis. 

We conducted post-hoc comparisons and 

corrected for multiple comparisons with a 

Bonferroni joint estimation procedure (Neter 

et al. 1990). We calculated the proportion of 

July caribou movements falling into each of 

5 movement rate categories (0–83, 84–330, 

331–821, 822–3300, >3300 ft/h; 0–25, 26–100, 

101–250, 251–1000, >1000 m/h) for all movements in each of 4 areas (Kogru Area, Smith 

Area, North of Teshekpuk Lake, and all other 

locations in the study area).

Weather Data

Parrett (2007) collected temperatures and 

wind speeds for 2 locations near Teshekpuk 

Lake during summer 2004 (Figure 1). The 

Marty’s Strip weather station was located 

approximately 9 mi (15 km) south of Teshekpuk Lake (lat 70.358°N, long 153.206°W), and 

the Lonely weather station was located on 

the Beaufort Sea coast directly north of Teshekpuk Lake (lat 70.910°N, long 153.215°W). 

Additional weather information was collected 

from the NOAA Earth System Research 

Laboratory at Barrow, Alaska (lat 71.323°N, 

long 156.611°W). 

Results

Satellite Collars

Caribou outfitted with satellite collars 

frequently used the constricted zones on 

either side of Teshekpuk Lake during midsummer (Figure 2). Based on satellite-collar 

locations, the estimated proportion of collared caribou with at least one location per 

half-month time period in the area north of 

Teshekpuk Lake peaked at 73% during early 

July (Figure 3). This proportion dropped 

sharply during other periods; little use of the 

area occurred outside the summer months. 

The proportion of collared caribou in the 

Kogru Area was consistently higher than 

the proportion in the Smith Area. A similar 

pattern was observed for the proportion of 

satellite-collared caribou traversing constricted zones (Figure 4). An estimated 38% 

and 50% of satellite-collared caribou crossed 

the Smith Area and Kogru Area, respectively, 

during early July. A slightly higher proportion of caribou moved north across the Smith 

Area than moved south. In contrast, a higher 

proportion moved south across the Kogru Area 

than moved north. 

The proportion of satellite-collared caribou 
BLM Open File Report 125 • July 2011 5

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

Figure 2. The locations of 102 caribou outfitted with satellite collars around the 2 constricted 

zones near Teshekpuk Lake, Alaska, 1990–2007.
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BLM Open File Report 125 • July 2011

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

moving across the constricted zones 

varied widely among years (Figure 

5). The estimated percentage of 

caribou crossing the zones ranged 

from 14% to 83% for the Smith Area 

and from 17% to 77% for the Kogru 

Area. The proportion crossing the 2 

different constricted zones within a 

year were not correlated (R = 0.564, 

P = 0.114).

These analyses of satellite-collared 

caribou were limited by the frequency 

of satellite locations acquisition, 

generally 1 location every 2 days 

during the summer, and by missing 

locations. Some movements across 

constricted zones may have been 

missed if they were of limited 

duration.

GPS Collars

Caribou outfitted with GPS collars 

frequently used the constricted zones 

on either side of Teshekpuk Lake 

during midsummer, especially 

during 2004 (Tables 1 and 2; Figures 

6 and 7). In July 2004, all 10 GPScollared caribou moved from north 

of the lake southward through the 

Kogru Area, some of them multiple 

times (Table 1). All 10 caribou had 

been captured north of Teshekpuk 

Lake in early July. Eight of the 

caribou made a circular, clockwise 

movement around Teshekpuk Lake, 

moving south through the Kogru 

Area from 6 to 8 July, north through 

the Smith Area from 20 to 22 July, 

and then south again through the 

Kogru Area on 27 July. The remaining 2 collared caribou also moved 

south through the Kogru area on 

27 July.

The apparent reasons for these 

movement patterns are supported by 

weather observations in July 2004 

(Figure 8). Barrow, which is exposed 

to both the Chukchi and Beaufort 

seas, generally has cooler temperatures and higher wind speeds than 

Lonely, the coastal site north of 

Teshekpuk Lake. The Lonely site, 

0

0.2

0.4

0.6

0.8

1

Proportion of Caribou 

In Smith Area

In Kogru Area

N. of Teshekpuk Lake

Figure 3. The mean proportion (±1 standard error) of satellite-collared caribou with at least one location in constricted 

zones or north of Teshekpuk Lake, Alaska, during each of 24 

two-week time periods per year, 1990–2007.

0

0.1

0.2

0.3

0.4

0.5

0.6

Proportion of Caribou 

N. Through Smith

S. Through Smith

Total Smith

0

0.1

0.2

0.3

0.4

0.5

0.6

Proportion of Caribou 

N. Through Kogru

S. Through Kogru

Total Kogru

Smith Area

Kogru Area

Figure 4. The mean proportion of satellite-collared caribou 

crossing each constricted zone near Teshekpuk Lake, Alaska, 

by direction of travel and total, during each of 24 two-week 

time periods per year, 1990–2007.
BLM Open File Report 125 • July 2011 7

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

in turn, is generally cooler than our 

inland site, Marty’s Strip. In 2004, 

high temperatures were measured 

in Barrow during the first few 

days of July. During this period 

caribou moved to the area north of 

Teshekpuk Lake where that year’s 

GPS-collaring operations occurred. 

The weather was cooler from 6 to 

8 July, when 8 of 10 GPS-collared 

caribou moved south through the 

Kogru Area, and conditions generally remained cooler (albeit with 

some brief, intra-day spikes) and 

also windier until 20 July. During 

that period, the 8 caribou that had 

moved south through the Kogru Area 

from 6 to 8 July remained inland 

and drifted west past the Ikpikpuk 

River. This cooler period was followed by a sustained period of warm weather 

with less wind from about 21 to 26 July, with 

temperatures somewhat cooler (but still high) 

at Lonely than at Marty’s Strip. During this 

warmer period, caribou again moved north of 

Teshekpuk Lake, this time through the Smith 

Area. After temperatures dropped considerably and wind speed increased on 27 July, all 

0

0.2

0.4

0.6

0.8

1

1.2

91-95 1996 97-01 2002 2003 2004 2005 2006 2007

Proportion of Caribou

Year

Smith

Kogru

Figure 5. The mean proportion (±1 standard error) of satellite-collared caribou crossing each of the 2 constricted zones 

near Teshekpuk Lake, Alaska, during July, 1991–2007. Some 

years were grouped together due to small sample sizes.

Table 1. Number of times (number of individual caribou) GPS-collared caribou entered constricted 

zones near Teshekpuk Lake, Alaska, by year, month, and movement direction. No caribou entered the 

constricted zones during November–May of any year. Ten caribou were collared from early July 2004 to 

early July 2005, 12 caribou were collared from early July 2006 to late June 2007, and 2 collared caribou 

died in spring 2007.

Kogru Area Smith Area

Year Month # Caribou S to Sa S to Nb N to Nc N to Sd S to S S to N N to N N to S

2004 July 10 0 2 (2) 7 (4) 19 (10) 2 (2) 7 (7) 0 0

August 10 3 (1) 1 (1) 0 1 (1) 0 0 0 0

September 10 0 0 0 0 0 2 (2) 0 0

October 10 0 0 0 3 (3) 0 1 (1) 0 0

2005 June 10 3 (3) 1 (1) 0 1 (1) 0 0 0 0

2006 July 12 8 (5) 6 (5) 3 (2) 3 (3) 0 3 (3) 2 (2) 4 (4)

August 12 0 0 0 2 (2) 0 0 0 0

September 12 0 0 0 0 0 0 0 0

October 12 0 0 0 0 0 0 0 0

2007 June 10 0 2 (2) 2 (1) 0 0 0 0 0

 

aSouth to South = caribou entered constricted zone from the south and exited to the south.

bSouth to North = caribou entered constricted zone from the south and exited to the north.

cNorth to North = caribou entered constricted zone from the north and exited to the north.

dNorth to South = caribou entered constricted zone from the north and exited to the south.
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Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

Table 2. Number of GPS-collared caribou entering the constricted zones on either side of 

Teshekpuk Lake, Alaska, 2004–2007.

Kogru Area Smith Area

Datea S to Sb S to Nc N to Nd N to Se S to S S to N N to N N to S

06-Jul-04 2 4

07-Jul-04 2 3

08-Jul-04 1 1

18-Jul-04 1

20-Jul-04 2 4

21-Jul-04 1 2

22-Jul-04 1 2 1

23-Jul-04 2

27-Jul-04 8

03-Aug-04 1

07-Aug-04 1

17-Aug-04 1

18-Aug-04 1

21-Aug-04 1

30-Sep-04 2

01-Oct-04 1

02-Oct-04 2

11-Oct-04 1

12-Jun-05 1

14-Jun-05 1

18-Jun-05 1 1

30-Jun-05 1

10-Jul-06 1

11-Jul-06 1 1

12-Jul-06 2

13-Jul-06 2

14-Jul-06 1 1

15-Jul-06 3

17-Jul-06 1 1 1 1

18-Jul-06 1 1

20-Jul-06 1

21-Jul-06 3

22-Jul-06 1

24-Jul-06 1 1

26-Jul-06 1

28-Jul-06 1

30-Jul-06 1

31-Jul-06 1

01-Aug-06 1

06-Aug-06 1

10-Jun-07 1

18-Jun-07 1

20-Jun-07 1

22-Jun-07 1

Total 14 12 11 29 2 13 2 4

aDate caribou left constricted zone. 

bSouth to South = caribou entered constricted zone from the south and exited to the north.

cSouth to North = caribou entered constricted zone from the south and exited to the north.

dNorth to North = caribou entered constricted zone from the north and exited to the north. 

eNorth to South = caribou entered constricted zone from the north and exited to the south.
BLM Open File Report 125 • July 2011 9

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

10 collared caribou moved south through the 

Kogru Area. 

In 2006, no pattern of clockwise movement 

around Teshekpuk Lake was apparent among 

the GPS-collared caribou. Five of 12 caribou 

traveled north through the Kogru Area, 

3 traveled south through the Kogru Area, 

3 traveled north through the Smith Area, 

and 4 traveled south through the Smith Area. 

Only 2 caribou used the corridors in August 

and none between September 2006 and May 

2007. Only 2 different caribou moved through 

the corridors in June 2007, although the 

collars were removed around 25 June 2007. 

The temporary weather stations at Lonely 

and Marty’s Strip (Figure 8) were not present 

in 2006, so no local weather observations are 

available for that summer.

Caribou moved fastest in July and slowest

in June (Table 3). They generally moved 

slower north of Teshekpuk Lake than in 

either constricted zone. There was a significant 2-way interaction between year and 

area for July movement rates (P <0.001). In 

2004, caribou moved slower north of Teshekpuk Lake than in the Kogru Area (P < 0.001)

or the Smith Area (P = 0.005), but there 

was no significant difference between the 

Kogru and Smith areas (P = 1.00). In 2006, 

caribou moved faster in the Smith Area than 

north of Teshekpuk Lake (P = 0.008) or the 

Kogru Area (P = 0.014), but there was no 

significant difference between the Kogru 

Area and the area north of Teshekpuk Lake 

(P = 1.00). The combined 2004 and 2006 data 

for July showed that fewer caribou moved 

very rapidly (>3,300 ft/h; >1,000 m/h) north 

of the lake than in the constricted areas and 

that few caribou moved at the slowest rate 

category (<83 ft/h; <25 m/h) within the Smith 

Area (Figure 9).

Caribou traveling through the constricted 

zones showed no distinct pattern in their 

movement rates by direction of movement 

(Table 4). However, caribou appeared to move 

at slower rates and take a longer period of 

time to traverse the constricted zones while 

moving south than while moving north.
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Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

Figure 6. The locations and movements of 10 caribou outfitted with GPS collars (recording locations 

every 3 hours) around the 2 constricted zones near Teshekpuk Lake, Alaska, July 2004–June 2005.
BLM Open File Report 125 • July 2011 11

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

Figure 7. The locations and movements of 12 caribou outfitted with GPS collars (recording locations 

every 2 hours) around the 2 constricted zones near Teshekpuk Lake, Alaska, July 2006–June 2007.
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Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

 

-5

0

5

10

15

20

25

30

Temperature (°C)

Barrow

Marty's Strip

Lonely

0

2

4

6

8

10

12

14

Wind Speed (m/s)

Date

Figure 8. Temperatures (°C) and wind speeds (m/s) at Barrow, 

Lonely, and Marty’s Strip, Alaska, during July 2004.

Table 3. Movement rates (km/h) of GPS-collared caribou north of Teshekpuk Lake and in 

constricted zones on either side of Teshekpuk Lake, Alaska, 2004–2007 based on distance between 

locations 2 or 3 h apart. Movement rate based on locations taken 3 h apart were multiplied by 

1.056 to adjust for the longer fix interval.

North of Teshekpuk Lake Kogru Area Smith Area

Year Month Average n SE Average n SE Average n SE

2004 Jul 0.70 612 0.03 1.45 123 0.13 1.16 57 0.16

Aug 0.52 25 0.11 0.40 56 0.05 – – –

Sep 0.58 7 0.22 – – – 1.83 5 0.24

Oct 0.47 76 0.06 0.97 26 0.18 2.95 3 0.86

2005 Jun 0.17 3 0.03 0.21 164 0.02 1.14 1 –

2006 Jul 0.88 430 0.05 1.02 169 0.10 1.63 38 0.3

Aug 0.60 58 0.14 0.75 17 0.17 – – –

2007 Jun 0.18 218 0.02 0.43 52 0.11 – – –

All Months 

Combined 0.65 1429 0.02 0.77 607 0.04 1.41 103 0.14
13 BLM Open File Report 125 • July 2011

Table 4. Movement rates (km/h) of GPS-collared caribou that crossed constricted zones near Teshekpuk Lake and 

crossing.

Kogru Area Smith Area

S to Na N to Sb S to N 

Year Month Average n SE Average n SE Average n SE Aver

Rate 2004 Jul 1.60 2 0.09 1.77 19 0.15 1.32 7 0.26 – 

Aug 0.28 1 – 0.73 1 – – – – – 

Sep – – – – – – 1.34 2 0.19 – 

Oct – – – 1.34 3 0.45 2.65 1 – – 

2005 Jun 0.44 1 – 0.17 1 – – – – – 

2006 Jul 1.50 6 0.22 1.61 3 0.97 3.19 3 1.28 1.9

Aug – – – 0.73 2 0.00 – – – – 

2007 Jun 0.69 2 0.22 – – – – – – – 

All Months

Combined 1.19 12 0.18 1.55 29 0.15 1.85 13 0.37 1.9

Duration 2004 July 27.00 2 0.004 12.00 19 1.45 21.00 7 4.72 – 

Aug 44.99 1 – 23.99 1 – – – – – 

Sep – – – – – – 7.50 2 1.50 – 

Oct – – – 27.00 3 15.00 9.00 1 – – 

2005 Jun 51.00 1 – 159.00 1 – – – – – 

2006 Jul 18.00 6 3.69 24.00 3 13.62 6.00 3 2.31 10.9

Aug – – – 24.00 2 6.00 – – – – 

2007 Jun 41.00 2 25.00 – – – – – – – 

All Months 

Combined 28.33 12 5.09 21.11 29 5.44 14.54 13 3.22 10.9

aSouth to North=caribou entered constricted zone from the south and exited to the north.bNorth to South=caribou entered constricted zone from the north and exited to the south.
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Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

0%

25%

50%

75%

100%

Smith Kogru North Other

Percentage

Area

>1000

251-1000

101-250

26-100

0-25

Figure 9. Movement rates of 22 GPS-collared caribou in 4 geographic 

areas by 5 movement categories (meters/hour) in July 2004 and July 

2006. The 4 geographic areas are the Smith Area, Kogru Area, North of 

Teshekpuk Lake, and the remainder of the study area (Other).

Discussion

During the insect season, which generally 

occurs from late June through early August, 

avoidance of insects often takes precedence 

over optimal foraging in shaping caribou 

behavior on the coastal plain (White et al. 

1975; Roby 1978; Dau 1986; Lawhead 1988). 

Mosquito activity peaks on warm, relatively 

calm days. Parrett (2007) suggests that 

wind speed may be more important than 

temperature in determining the severity of 

mosquito harassment. His data indicate that 

mosquito activity, although proportional to 

temperature, occurs across the range of July 

temperatures. Wind speed, however, acts as a 

threshold variable, with speeds above 9 mi/h 

(4 m/s) keeping mosquito activity below high 

levels. During insect harassment the daily 

energy budget of a lactating female caribou 

may suffer a negative balance (Fancy 1986), 

which may in turn reduce the female’s probability of bearing a calf the following spring 

(Cameron et al. 1993; Cameron 1994).

As previously reported (Person et al. 2007), 

the constricted zones around Teshekpuk Lake 

are important movement corridors for caribou 

moving north of Teshekpuk Lake for mosquito 

relief. Satellite-collar data indicate that these 

areas may be used throughout the year (Prichard and Murphy 2004), but most movement 

across the constricted zones occurs in July, 

the period of greatest mosquito activity. These 

patterns were generally known from field 

observations prior to the use of satellite collars 

(Davis and Valkenburg 1979; Silva et al. 1985), 

but our data quantify both use and variation 

among years. 

Both TCH and Central Arctic Herd caribou 

summer on the Arctic Coastal Plain, and when 

harassed by mosquitoes, move upwind (generally northeastward) to reach mosquito-relief 

habitats (Murphy and Lawhead 2000). They 

move back inland to better foraging habitat 

when mosquito activity decreases (Smith 1996). 

Our data from both satellite- and GPScollared caribou show a tendency of TCH 

caribou to move in a clockwise pattern around 

Teshekpuk Lake, although caribou do move 

both directions through both corridors. Just 

as temperature and wind speed may explain 

the timing of caribou movements to the north 

of the lake versus inland, we hypothesize that 

wind direction and the lake’s position in the 

middle of the herd’s July range may drive this 

tendency for a clockwise movement. During 

low mosquito activity, caribou tend to move 

with the predominantly northeasterly winds as 

they forage, heading away from mosquito-relief 

areas. If mosquito activity remains low for long 

enough, caribou are likely to end up west or 

southwest of the lake. Then when mosquito 
BLM Open File Report 125 • July 2011 15

Caribou Use of Narrow Land Corridors around Teshekpuk Lake, Alaska

activity increases again, caribou head upwind, 

returning to relief habitat via the quickest 

route, i.e., through the Smith Area. The headwind helps decrease insect harassment during 

the return trip to the mosquito-relief area. As 

this weather/insect regime continues, further 

caribou movement into the wind is limited 

by the sea coast northeast of the lake. Then 

when mosquito activity once again abates, 

the shortest route inland is south through the 

Kogru Area. 

Our GPS-collar data indicate this clockwise 

pattern in 2004 but not in 2006. Because 

caribou movements are influenced by weather 

patterns that vary among years, additional 

years of GPS-collar data, in conjunction with 

local weather observation stations north and 

south of the lake, are needed to confirm the 

frequency of the clockwise movements.

Due to their short fix intervals, GPS collars 

provide the best evidence of specific caribou 

movement paths and rates of movement both 

within the constricted zones and elsewhere. 

Observed variation in movement rates is consistent with use of the area north of Teshekpuk 

Lake for mosquito relief. Movement rates are 

fastest during July, when mosquito activity is 

usually greatest. During July, movements are 

slower north of the lake, where mosquito activity is lower, than they are in areas that have 

greater potential for mosquito harassment. 

Movements tend to be faster when caribou are 

headed north toward mosquito-relief areas 

than when headed south under reduced insect 

stress. Our failure to observe a larger difference in movement rates by direction may be an 

artifact of our relatively small sample size of 

GPS-collar locations.

Management Implications 

If oil field development were to hinder 

caribou from reaching mosquito-relief habitat 

north of Teshekpuk Lake, the consequent 

energetic stress might result in lower fecundity and ultimately reduced population size 

(Cameron 1994, 1995). The BLM has already 

acknowledged the importance of the Teshekpuk Lake area, including the 2 constricted 

zones, to the TCH (USDOI BLM 2008). Our 

results not only confirm but quantify both spatial and temporal aspects of that importance. 

Results from our GPS-collar data suggest that 

caribou do not consistently favor specific paths 

to cross the constricted zones, so there may 

not be a “best” pipeline route through either 

zone. Similarly, if direction of caribou movement relative to the orientation of oil field 

infrastructure is an important consideration, 

our data do not confirm a consistent pattern; 

a clockwise movement is apparent in one year 

but not another. Thus there may not be a best 

orientation.

Alternatively, further studies may yet 

reveal identifiable trends in paths used by caribou as well as in their directions of movement 

through the constricted zones. Our GPS-collar 

results are based on a relatively small sample 

of 22 caribou over just 2 years. The more 

extensive satellite-collar dataset displays 

ample variability among years. Although the 

higher-resolution GPS-collar data provide 

better information on which to base management decisions, we will require additional 

years of data collection to discern real trends 

within the natural variability. The BLM needs 

to stay engaged in the collection of that data. 

In addition, the agency should require an 

updated analysis including all new location 

data before approving any future pipelines 

through one or both constricted zones.

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