U.S. Department of the Interior

U.S. Geological Survey

Data Series 1121

Supersedes USGS Data Series 568

Catalogue of Polar Bear (Ursus maritimus) Maternal Den 

Locations in the Beaufort and Chukchi Seas and Nearby 

Areas, 1910–2018
Cover: Adult female polar bear and her two cubs traveling across the sea ice of the 

Arctic Ocean north of the Alaska coast, April 2008. Photograph by Mike Lockhart, 

U.S. Geological Survey.
Catalogue of Polar Bear (Ursus maritimus)

Maternal Den Locations in the Beaufort 

and Chukchi Seas and Nearby Areas, 

1910–2018

By George M. Durner, Steven C. Amstrup, Todd C. Atwood, David C. Douglas, 

Anthony S. Fischbach, Jay W. Olson, Karyn D. Rode, and Ryan R. Wilson

Data Series 1121

Supersedes USGS Data Series 568

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DAVID BERNHARDT, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2020

Supersedes USGS Data Series 568

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation: 

Durner, G.M., Amstrup, S.C., Atwood, T.C., Douglas, D.C., Fischbach, A.S., Olson, J.W., Rode, K.D., and Wilson, R.R., 

2020, Catalogue of polar bear (Ursus maritimus) maternal den locations in the Beaufort and Chukchi Seas and nearby 

areas, 1910–2018: U.S. Geological Survey Data Series 1121, 12 p., including appendixes, 

https://doi.org/10.3133/ds1121. [Supersedes USGS Data Series 568.]

Associated data for this publication: 

Durner, G.M., 2010, Catalogue of polar bear (Ursus maritimus) maternal den locations in the Beaufort and Chukchi 

seas and nearby areas, 1910–2018 (ver. 2.0, January 2020): U.S. Geological Survey data release, https://doi.

org/10.5066/P9RPHH50.

ISSN 2327-638X (online)
iii

Contents

Abstract...........................................................................................................................................................1

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

Methods of Discovery...................................................................................................................................2

Distribution of Den Locations.......................................................................................................................5

Summary and Data Availability....................................................................................................................8

Acknowledgments.........................................................................................................................................8

References Cited............................................................................................................................................8

Appendix 1. Determination of Spatial Uncertainty.................................................................................10

Appendix 2. Dens Appearing in Durner and Others (2010) That Are Excluded From This

Data Series and Its Associated Data Release ..........................................................................11

Appendix 3. Definition of Categorical Data Codes .................................................................................12

Figures

1. Photograph showing female polar bear emerging from her maternal den

adjacent to a coastal bank on Foggy Island, near Prudhoe Bay, Alaska, April 2009 ........2

2. Maps showing distribution of polar bear maternal dens discovered through

satellite telemetry, very high frequency (VHF) telemetry, reported by others, and

during polar bear survey operations on sea ice and nearshore areas, for the

Beaufort and Chukchi Seas and neighboring regions,1910–2018 ........................................6

3. Map showing distribution of polar bear maternal dens discovered through

Forward-Looking Infrared (FLIR) sensor surveys of terrestrial denning habitat in

the Prudhoe Bay region of the Beaufort Sea coast, 1999–2017............................................7

4. Maps showing distribution of polar bear maternal dens discovered by very high

frequency (VHF) telemetry during 1981–91 when most data were collected

through systematic surveys, and after 1991 when VHF telemetry missions only

occurred near shore in the Beaufort Sea.................................................................................7
iv

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

mile, nautical (nmi) 1.852 kilometer (km)

International System of Units to U.S. customary units

Multiply By To obtain

Length

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Datums

Field observations made prior to 1995 were recorded in North American Datum of 1927 and 

post-projected to the World Geodetic System 1984 (WGS84). All satellite-tag locations, and field 

observations made after 1994, were recorded in WGS84.
Catalogue of Polar Bear (Ursus maritimus) Maternal Den 

Locations in the Beaufort and Chukchi Seas and Nearby 

Areas, 1910–2018

By George M. Durner1, Steven C. Amstrup2, Todd C. Atwood1, David C. Douglas1, Anthony S. Fischbach1, Jay 

W. Olson3, Karyn D. Rode1, and Ryan R. Wilson4

1

U.S. Geological Survey

2

Polar Bears International

3

U.S. Forest Service

4

U.S. Fish and Wildlife Service

Abstract

This report presents data on the approximate locations 

and methods of discovery of 530 polar bear (Ursus maritimus) 

maternal dens observed in the Beaufort and Chukchi Seas 

and neighboring areas from 1910 to 2018, and archived partly 

by the U.S. Geological Survey, Alaska Science Center, and 

partly by the U.S. Fish and Wildlife Service, Marine Mammals 

Management, in Anchorage, Alaska. A description of data 

collection methods and their associated biases, primary data 

collection time periods, and estimated position uncertainty are 

provided. Polar bears in the Beaufort and Chukchi Seas den 

on sea ice and land. Standardized very high frequency (VHF) 

aircraft surveys and satellite radio telemetry data provide a 

general understanding of where polar bears have denned in 

this region over the past 3 decades. Den observations made 

during other research activities and anecdotal reports from 

other government agencies, coastal residents, and industry 

personnel also are reported. These data on past polar bear 

maternal den locations are provided to inform decision making 

by natural resource agencies and for public use.

Introduction

Polar bears (Ursus maritimus) require dens of snow and 

ice that remain undisturbed throughout den tenure for the 

successful parturition and early development of neonates. 

Suitable denning habitat generally occurs on the leeward 

side of terrestrial banks and bluffs, or sea ice pressure ridges, 

where drifting snow can accumulate (Durner and others, 

2003; fig. 1). A large proportion of polar bear maternal dens 

observed in the Beaufort and Chukchi seas have occurred on 

drifting pack ice rather than land, making bears in this region 

unique relative to those in other parts of their circumpolar 

range (Amstrup and Gardner, 1994; Fischbach and others, 

2007; Rode and others, 2018). In northern Alaska and adjacent 

areas in Canada, denning habitat and the timing of maternal 

denning may overlap with industrial activities, presenting 

a potential for negative interactions between polar bears 

and humans. Given this rigid life history requirement and 

an increasing human presence in the Arctic, the distribution 

of maternal denning is considered important information 

for management decisions that have implications in the 

conservation of polar bears.

This report and the associated data release (Durner, 2020) 

provide potential users with point locations of polar bear 

maternal dens observed in the marine and terrestrial habitats 

of the Beaufort and Chukchi Seas, 1910–2018. Its primary 

purpose is to inform natural resource agencies in their efforts 

to minimize interactions between human activities and polar 

bear maternal dens. The den data are a mix of anecdotal 

observations, reports from other governmental agencies, nonstandardized and standardized surveys, and satellite telemetry 

records. The polar bear maternal den records presented 

here supersede an earlier version of these data (Durner and 

others, 2010).
2 Catalogue of Polar Bear (Ursus maritimus) Maternal Den Locations in the Beaufort and Chukchi Seas and Nearby Areas, 1910–2018

Figure 1. Female polar bear emerging from her maternal den adjacent to a coastal bank on 

Foggy Island, near Prudhoe Bay, Alaska, April 2009. Photograph by Rusty Robinson, Brigham 

Young University, Provo, Utah. Used with permission.

Methods of Discovery

Data in this report span more than a century of polar 

bear maternal den observations by residents and visitors to 

the Arctic, industry personnel, and natural resources agencies 

of Borough, State, and Federal governments. From 1965 to 

1972, polar bear research and management was under the 

jurisdiction of the Alaska Department of Fish and Game 

(ADFG), including the recording of polar bear maternal dens 

(Lentfer and Hensel, 1980). Following passage of the Marine 

Mammal Protection Act in 1972, all polar bear research and 

management were transferred to separate divisions of the U.S. 

Fish and Wildlife Service (FWS). In 1993, most Department 

of the Interior (DOI) biological research was moved into the 

National Biological Survey (under Secretarial Order 3173) 

and later renamed the National Biological Service (under 

Secretarial Order 3185). Another transfer of DOI research 

occurred in 1996 when the National Biological Service 

was moved into the U.S. Geological Survey (USGS) as the 

Biological Resources Division (Wagner, 1999). Because these 

different agencies housed a continuation of the same research 

program, they are collectively referred to as the USGS. 

In 2008 the FWS, Marine Mammals Management Office, 

assumed research efforts in the Alaska Chukchi Sea, including 

the capture and radio-tagging of adult female polar bears and 

the identification of maternal dens.

Prior to 1980, most data on polar bear maternal dens in 

the Beaufort and Chukchi Seas were observations collected 

through interviews of coastal residents, guides of polar bear 

hunters, and industry personnel (Lentfer and Hensel, 1980). 

Additional observations were made during autumn fixedwing aircraft surveys of nearshore habitats by the ADFG 

(during 1965, 1967, and 1971), the FWS (during 1973, 1974, 

and 1976), and by the FWS (during March and April 1973, 

1974, and 1975; Lentfer and Hensel, 1980). Opportunistic 

observations of maternal dens were recorded during spring 

(March and April) mark-recapture research (Lentfer, 1975; 

Lentfer and others, 1980) in northwestern and northern 

Alaska by the ADFG (during 1967–72) and the FWS (during 

1974–76).

Federal research of polar bears expanded greatly 

beginning in 1980 with an intensification of mark-recapture 

and animal-tracking efforts. From 1980 through 1994, capturemark-recapture efforts focused on estimating the population 

size of polar bears in the southern Beaufort Sea (Amstrup 

and others, 1986, 2001). These efforts involved 4–6 weeks of 

fieldwork each spring and 4–5 weeks during some autumns. In 

1981, radio tracking began after the development of very high 

frequency (VHF) radio transmitter collars that were suitable 

for deployment on adult female polar bears. In 1985, the 

USGS began deployment of satellite-linked radio transmitters 

(Platform Transmitter Terminal, or PTT) on polar bears in the 

Beaufort and Chukchi Seas (Fancy and others, 1988). 
Methods of Discovery 3

PTT signals received by satellites were processed by the 

ArgosTM system (Collecte Localisation Satellites, or CLS; 

Toulouse, France; http://www.argos-system.org/), which then 

provided users with estimates of PTT location and sensor data 

(that is, activity and temperature of the transmitter). Beginning 

in 2004, most PTTs deployed by the USGS were equipped 

with Global Positioning System (GPS) receivers, the data of 

which were sent to satellites as a sensor string. In 2014, the 

USGS began deployment of transmitters that relayed GPSbased location and sensor data through the Iridium® Satellite 

Communications system (Iridium Satellite Communications, 

McLean, Virginia). Hereinafter, we refer to both PTTs and 

Iridium radios as satellite-linked tags.

Several methods were used to collect observations on 

polar bear maternal dens. Standardized VHF surveys in the 

eastern Chukchi Sea, Beaufort Sea, and northwestern Canada 

were done by aircraft four times each winter during 1983–87, 

and twice each winter during 1988–91 (Amstrup and Gardner, 

1994) to locate polar bear maternal dens. Following 1985, 

location and sensor data from satellite-linked tags deployed 

on female polar bears in the Beaufort and Chukchi Seas 

enabled the remote identification of maternal dens (Amstrup 

and Gardner, 1994; Fischbach and others, 2007; Garner and 

others, 1990; Olson and others, 2017; Rode and others, 2018). 

Additionally, the USGS recorded observations reported by 

Borough, State, and Federal agencies, as well as observations 

by local residents, industry personnel, and other groups 

visiting Arctic coastal regions in Alaska. Most reported 

observations were provided to the USGS by the FWS, Marine 

Mammals Management. Maternal dens also were observed 

and recorded by USGS personnel incidental to standard 

searches for polar bears during nearshore capture-recapture 

and radio-collaring efforts. The development of VHF radio 

tags, combined with standardized high-altitude radio-tracking 

surveys and the deployment of satellite-linked tags, provided 

data of maternal dens that were largely free from geographic 

biases inherent in other types of observations. Data resulting 

from these tracking methods allowed a better understanding of 

the distribution and timing of polar bear maternal denning.

Following a short hiatus in data collection that began 

in 1995, the USGS resumed polar bear field research in 

autumn 1997 in the Beaufort Sea (Regehr and others, 2006; 

Bromaghin and others, 2015). Autumn field research ceased 

after 2001 because of delayed autumn ice formation that had 

become common and prevented reliable autumn captures. 

From 1997 to 2016, the USGS continued to deploy satellitelinked and some VHF radio tags. Beginning in 2008, the FWS 

deployed satellite-linked tags on adult female polar bears in 

the eastern Chukchi Sea during spring field seasons. Since the 

publication by Amstrup and Gardner (1994), assessments of 

the distribution of maternal denning have been done mostly 

with sensor and location data derived from satellite-linked 

tags (Fischbach and others, 2007; Olson and others, 2017; 

Rode and others, 2018). However, additional data were 

collected through restricted VHF telemetry surveys over the 

nearshore Alaska Beaufort Sea; experimental surveys with 

Forward-Looking Infrared (FLIR; Amstrup and others, 2004) 

over likely polar bear denning habitat (Durner and others, 

2003); and reports from local residents, industry personnel, 

and visitors to northern Alaska.

The FWS-Marine Mammals Management and the Alaska 

Department of Fish and Game provided additional den records 

for 2006–18. Maternal dens were identified in polar bear 

denning habitat (Durner and others, 2003) on barrier islands 

and coastlines near the Prudhoe Bay oilfield (that is, from 146° 

40’ to 151° 00’ west longitude) through surveys with airborne 

FLIR, handheld infrared sensors, and trained scent dogs, and 

by industry reports. Confirmation of maternal dens was done 

following the methods described in Shideler (2014).

Because of the diversity of data sources and the substrate 

choice of polar bears (floating and mobile pack ice, immobile 

sea ice attached to land [that is, fast ice], or land), the spatial 

resolution of the den locations reported here varies. Most 

reported den observations were recorded to the nearest minute 

of latitude and longitude because they were estimated from 

a hunter’s memory of where a den was observed many years 

prior. Dens observed during aircraft VHF missions, or by 

USGS field crews conducting polar bear captures prior to 

1998, also were reported to the nearest minute of latitude 

and longitude. Likewise, den positions estimated from 

topographical maps were recorded to the nearest minute 

of latitude and longitude, and included the inherent spatial 

uncertainty associated with placement of a penciled dot on 

a physical map by the observer. Hence, for all den records 

whose positions were reported or were derived from aircraft 

or maps prior to regular use of GPS, we imposed a horizontal 

uncertainty of plus or minus 926 meters (m) (that is, one-half 

of 1 minute of latitude, or equivalently, one-half of 1 nautical 

mile) on the location.

Beginning in 1995, the USGS made use of military-grade 

GPS receivers to determine den locations during on-ground 

visits (appendix 1). Following 1998, all conventional, FLIR, 

and VHF radio-tracking aircraft missions used onboard GPS 

to record flight paths, mark locations of polar bears, and 

determine the location of maternal dens. Additionally, most 

satellite-linked tags used from 2004 and onward also had 

onboard GPS receivers. Whether field or satellite-tag derived, 

all GPS latitudes and longitudes were recorded to at least 

1/10,000th of a degree (that is, the nearest 0.006 minute of 

latitude and longitude) and were assumed to have a spatial 

error of less than or equal to 30 m. Locations provided through 

the Argos system were based on Doppler shifts measured 

during satellite overpass and satellite orbitography using 

least-squares processing methods (Lopez and others, 2014) 

and reported to 1/1000th of a degree (that is, the nearest 0.06 

minute of latitude and longitude). Because Argos location 

estimates sometimes are highly erroneous, we post-processed 

Argos data with the Douglas Argos-filter (Douglas and 

others, 2012), which evaluated spatial redundancy, movement 

rate, turning angle, and the Argos location class to identify 

improbable locations and to select between the reported 

primary and alternate locations generated by CLS. 
4 Catalogue of Polar Bear (Ursus maritimus) Maternal Den Locations in the Beaufort and Chukchi Seas and Nearby Areas, 1910–2018

Final quality of Argos locations, with 1-sigma (about 

68-percent) location error radius, ranged from 0.4 kilometers 

(km; highest quality) to 7.6 km (lowest quality) of the true 

PTT position (see table 2 in Douglas and others, 2012). 

Additional details on how spatial uncertainty was determined 

are provided in appendix 1.

Because sea ice continually drifts (except for nearshore 

fast ice) and can transport dens more than 100 km while 

occupied (Amstrup and Gardner, 1994), sea ice den locations 

are reported from a single field observation or a single 

satellite-linked position (generally a GPS or the best Argos 

quality record closest to the date after den entrance) and do 

not indicate the location of the den during the entire winter. 

In contrast, dens on land or fast ice remain stationary during 

den tenure. For land and fast ice dens whose positions were 

determined by satellite-linked data, we selected the record 

with the best location quality during den tenure. In cases of 

ties among the highest-quality locations, we averaged their 

coordinates and report that average.

Follow-up visits to dens, either by low-level aircraft 

reconnaissance or on-ground measures by personnel, resulted 

in improved estimates of den locations and verification of den 

occupancy. For example, many dens discovered by satellite 

telemetry during early winter were surveyed with aerial VHF 

telemetry in late winter. In such cases, the VHF telemetry 

location would supersede the previous satellite telemetryderived location. Likewise, dens may have been visited on 

the ground following their discovery by satellite telemetry or 

VHF telemetry. Because ground visits resulted in the most 

accurate den location, those locations superseded all prior 

estimates. This process typically resulted in minor changes of 

the recorded den location as new data became available. The 

records provided in this report are the best estimate of a den 

location as of 2019.

We excluded seven newly discovered dens from this data 

release because it was not possible to determine their position 

because of consistently poor PTT signal quality during den 

tenure. An additional seven dens that were listed in Durner 

and others (2010) also have been excluded after our review 

of these records indicated either insufficient data to support 

assignment as a den, absence of location data during den 

tenure, or identification of a duplicate record (see appendix 2).

Field descriptors for each data record include (1) 

the record number (Record); (2) the USGS-assigned den 

identification number (DenID); (3) the year during which the 

cubs would have emerged from the den (Spring_year); (4) the 

data source (Data_source); (5) the method used to discover the 

den (Discovery_method); (6) the latitude in decimal degrees 

(Latitude); (7) the longitude in decimal degrees (Longitude); 

(8) an indicator of confidence that the observation was truly 

a polar bear maternal den (Confirmation); (9) the substrate 

on which the den occurred (Substrate); (10) the method used 

to determine the position of the den (Position_method); and 

(11) an estimate of position error (Horizontal_error_m). 

Confirmed dens (that is, Confirmation = C) were those verified 

by on-site visits by personnel and (or) subsequent observations 

of the adult with dependent young. Probable dens (that is, 

Confirmation = P) were those with supporting information to 

indicate maternal denning (for example, temperature, activity, 

and signal quality of satellite telemetry data), but lacked a 

site visit or a subsequent observation of the adult with young. 

See appendix 3 for the definition of codes used in categorical 

fields.

Field observations made prior to 1995 were recorded 

in North American Datum of 1927 and post-projected to 

the World Geodetic System 1984 (WGS84). All satellitetag locations, and field observations made after 1994, were 

recorded in WGS84. The data provided here are maternal 

den locations, where “maternal den” represents a structure 

that was used by a pregnant polar bear to give birth to young 

and, should parturition be successful, continue to be used 

as shelter for developing neonates until late winter or early 

spring when the family group would depart the den. Whether a 

structure was a maternal den was determined by assessing the 

timing and duration of den tenure, and assessing temperature, 

activity, and signal quality from satellite-linked radio tags. 

In using these criteria, there could be dens reported here that 

were occupied by a female that was not pregnant. Messier and 

others (1994) reported that non-pregnant female polar bears in 

the Canadian Arctic Archipelago used snow dens as shelters 

for short periods during winter. We tried to avoid inclusion 

of non-maternal dens by either verifying that a female was 

unaccompanied by cubs during the spring and autumn prior to 

denning, was accompanied by first-year cubs after denning, or 

remained in a den for a duration typical of successful maternal 

dens (for example, Olson and others, 2017; Rode and other, 

2018). Direct observations of females with dependent young, 

visual inspection of the den following departure of the family, 

and visual inspection of the ground following snowmelt were 

used to confirm maternal denning. We excluded (1) USGS 

records of temporary dens not used for parturition, (2) autumn 

exploratory dens that apparently were not used or thought 

to be abandoned by the bear prior to parturition, (3) FLIR 

hotspots that later showed no evidence of being a maternal 

den, and (4) erroneous or questionable reports from other 

parties. Because these other observations were excluded, there 

are gaps in consecutive DenID records (see Durner, 2020).
Distribution of Den Locations 5

Distribution of Den Locations

We report a total of 530 polar bear maternal den records 

documented between 1910 and 2018 (see Durner, 2020, 

for the tabular data and metadata associated with this data 

series). PTT data analyzed by Rode and others (2018) from 

polar bears in the Chukchi Sea were the primary contributor 

to the increase in dens discovered by satellite radio telemetry 

(Discovery_method = SATELLITE) from 169 (Durner and 

others, 2010) to 266. The data release associated with this data 

series (Durner, 2020) also includes (1) observations reported 

by other individuals or institutions (Discovery_method = 

REPORT, n = 79), (2) observations from polar bear field 

research (Discovery_method = CONVENTIONAL, n = 54), 

(3) dens encountered by FLIR surveys (Discovery_method 

= FLIR, n = 30), and (4) dens located by VHF telemetry 

(Discovery_method = VHF_RADIO, n = 101). All VHF 

telemetry records were collected from 1982 to 2009, 

all satellite records were collected from 1986 to 2015, 

and all FLIR records were collected from 1999 to 2017. 

CONVENTIONAL observations were made from 1969 to 

2013. REPORT observations were made from 1910 to 2018.

The discovery method strongly influenced the observed 

distribution of den locations. Dens discovered by satellite 

tracking were distributed throughout the Beaufort and Chukchi 

Seas and northwestern Canada (fig. 2A), indicating the 

advantage of this method for minimizing observation bias. 

Dens discovered by VHF telemetry observations, however, 

were restricted to the eastern Chukchi Sea, Beaufort Sea, 

and northwestern Canada (fig. 2B), indicating the general 

logistical range of aircraft paths in collecting data over a large 

region (Amstrup and Gardner, 1994). Dens whose discovery 

method was reported (Discovery_method = REPORT; 

fig. 2C), discovered during polar bear field research operations 

(Discovery_method = CONVENTIONAL; fig. 2D) or 

discovered with Forward-Looking Infrared surveys for dens 

(Discovery_method = FLIR; fig. 3) occurred mostly nearshore 

and on land, indicating the logistical limitations of where 

observers in the field conducted their activities and the spatial 

focus of industry surveys. The distribution of dens discovered 

by VHF telemetry also was dependent on the time period 

during which the data were collected. Whereas VHF telemetry 

data collected from 1983 to 1991 were through systematic 

Beaufort Sea and eastern Chukchi Sea-wide surveys (Amstrup 

and Gardner, 1994), VHF telemetry missions after this period 

only surveyed nearshore regions (fig. 4).
6 Catalogue of Polar Bear (Ursus maritimus) Maternal Den Locations in the Beaufort and Chukchi Seas and Nearby Areas, 1910–2018

ALASKA

(U.S.A.)

CANADA RUSSIA

Chukchi 

Sea

Beaufort

Sea

ALASKA

(U.S.A.)

CANADA RUSSIA

Chukchi 

Sea

Beaufort

Sea

ALASKA

(U.S.A.)

CANADA RUSSIA

Chukchi 

Sea

Beaufort

Sea

ALASKA

(U.S.A.)

CANADA RUSSIA

Chukchi 

Sea

Beaufort

Sea

0 200 400 600 MILES

0 200 400 600 800 1,000 KILOMETERS

A. Satellite telemetry, n = 266 B. VHF telemetry, n = 101

C. Reported, n = 79 D. Conventional, n = 54

120°

140°

160°

180°

80°

70°

120°

140°

160°

180°

80°

70°

120°

140°

160°

180°

80°

70°

120°

140°

160°

180°

80°

70°

Base map from USGS and other digital data sources. 

Coordinate reference system: Clarke 1866 Albers, SP1=55°, 

SP2=65°, CM=−154°, LO=50°, FE=5,000000, FN=5,000,000. 

Horizontal datum is North American Datum of 1927. 

Figure 2. Distribution of polar bear maternal dens (hollow black circles) discovered through (A) satellite telemetry, (B) very high 

frequency (VHF) telemetry, (C) reported by others, and (D) during polar bear survey operations on sea ice and nearshore areas, for 

the Beaufort and Chukchi Seas and neighboring regions, 1910–2018.
Distribution of Den Locations 7

Deadhorse

Prudhoe

Bay

Beaufort

Sea

ALASKA

(U.S.A.)

Road

Pipeline

EXPLANATION

FLIR, n = 30

148°

150°

146°

70°

71°

0 10 20 30 MILES

0 10 20 30 40 50 KILOMETERS

Base map from USGS and other digital data sources. 

Coordinate reference system: Clarke 1866 Albers, SP1=55°, 

SP2=65°, CM=−154°, LO=50°, FE=5,000000, FN=5,000,000. 

Horizontal datum is North American Datum of 1927. 

Figure 3. Distribution of polar bear maternal dens (hollow black circles) discovered through ForwardLooking Infrared (FLIR) sensor surveys of terrestrial denning habitat in the Prudhoe Bay region of the 

Beaufort Sea coast, 1999–2017.

ALASKA

(U.S.A.)

CANADA RUSSIA

Chukchi 

Sea

Beaufort

Sea

ALASKA

(U.S.A.)

CANADA RUSSIA

Chukchi 

Sea

Beaufort

Sea

0 200 400 600 MILES

0 200 400 600 800 1,000 KILOMETERS

A. VHF telemetry to 1991, n = 72 B. VHF telemetry after 1991, n = 29

120°

140°

160°

180°

80°

70°

120°

140°

160°

180°

80°

70°

Base map from USGS and other digital data sources. 

Coordinate reference system: Clarke 1866 Albers, SP1=55°, 

SP2=65°, CM=−154°, LO=50°, FE=5,000000, FN=5,000,000. 

Horizontal datum is North American Datum of 1927. 

Figure 4. Distribution of polar bear maternal dens (hollow black circles) discovered by very high frequency (VHF) telemetry (A) during 

1981–91 when most data were collected through systematic surveys, and (B) after 1991 when VHF telemetry missions only occurred 

near shore in the Beaufort Sea.
8 Catalogue of Polar Bear (Ursus maritimus) Maternal Den Locations in the Beaufort and Chukchi Seas and Nearby Areas, 1910–2018

Summary and Data Availability

Records of maternal den locations in the Beaufort and 

Chukchi Seas and neighboring regions maintained by the U.S. 

Geological Survey, Alaska Science Center, are made available 

to resource managers and the public. Users are advised 

that observations of maternal dens, along with the spatial 

uncertainty and spatial bias of den locations, are dependent 

on the method of data collection; thus, certain methods will 

provide a better representation of den distribution than others.

Acknowledgments

The authors recognize the contributions of Gerald W. 

Garner (U.S. Geological Survey [USGS]) who deployed 

satellite collars on female polar bears in the Chukchi Sea 

from 1987 to 1994. We acknowledge Stanislav E. Belikov 

(All-Russian Research Institute for Nature Conservation and 

Reserves) and Mikial S. Stishov (Wrangel Island State Nature 

Reserve), whose collaboration with Gerald W. Garner made 

possible the deployment of satellite collars on polar bears 

along Russia’s Chukotka Peninsula and Wrangel Island. We 

wish to express our appreciation to numerous local residents 

and industry personnel whose observations added to the data 

in this report. Logistical support and (or) data were provided 

by the U.S. Fish and Wildlife Service, the U.S. Bureau 

of Land Management, the U.S. Bureau of Ocean Energy 

Management, BP Exploration – Alaska, ConocoPhillips – 

Alaska, ExxonMobil, Caelus Energy Alaska, Hilcorp Alaska, 

LLC, Eni Petroleum Co. Inc., Polar Bears International, the 

University of Wyoming (National Science Foundation grant 

OPP 0732713), and prior to 1973, the State of Alaska. We 

appreciate the constructive suggestions by Layne Adams 

(USGS), Craig Perham (U.S. Bureau of Ocean Energy 

Management), and Richard Shideler (Alaska Department of 

Fish and Game) on earlier versions of this data report.

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bear population status in the southern Beaufort Sea: U.S. 

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10 Catalogue of Polar Bear (Ursus maritimus) Maternal Den Locations in the Beaufort and Chukchi Seas and Nearby Areas, 1910–2018

Appendix 1. Determination of Spatial Uncertainty

Positions Determined By Global Positioning Systems (GPS)

Global Positioning System (GPS) location error was assumed to be less than or equal to 30 meters (m) (Adams and 

others, 2013). The U.S. Geological Survey (USGS) polar bear research program began using military GPS (that is, Precision 

Lightweight Global Positioning System Receiver [PLGR], Rockwell Collins, Cedar Rapids, Iowa) receivers in 1995. PLGRs 

were used in on-ground site visits of historical dens for habitat measurements. Routine use of civilian GPS for recording aircraft 

flight tracks and den locations began in 1999.

Positions Determined by Argos

Argos 1-sigma (68-percent) location error estimates after filtering with a plausibility algorithm: Location class quality 3, 

less than (<) 400 m; quality 2, <1,000 m; quality 1, <2,500 m; quality 0, <6,800 m; quality A, <4,100 m; quality B, <7,600 m; 

quality Z, <4,700 m (Douglas and others, 2012).

Positions Determined by VHF-Aided or Conventional Aircraft Searches Before GPS (That is, Most 

Records Prior to 1999) and Positions Reported by Others

Most den locations in this category were recorded to the nearest minute of latitude and longitude. Hence, we assumed 

a location error of 0.5 nautical miles (that is, one-half a latitude degree minute), or 926 m. We assumed that the position of 

reported dens was made with topographical maps.
Appendix 2 11

Appendix 2. Dens Appearing in Durner and Others (2010) That Are Excluded From 

This Data Series and Its Associated Data Release

[DenId: U.S. Geological Survey-assigned den identification number]

DenID Reason for exclusion

547 Data review revealed no compelling evidence that this was a maternal den.

625 Review of Argos data found no locations during den tenure.

723 Data review revealed no compelling evidence that this was a maternal den.

855 Review of Argos data found no locations during den tenure.

969 Data review revealed no compelling evidence that this was a maternal den.

973 Duplicate of DenID 972 (Forward-Looking Infrared discovery).

989 Data review revealed no compelling evidence that this was a maternal den.
12 Catalogue of Polar Bear (Ursus maritimus) Maternal Den Locations in the Beaufort and Chukchi Seas and Nearby Areas, 1910–2018

Appendix 3. Definition of Categorical Data Codes

Code Definition

Data_source

ADFG Alaska Department of Fish and Game

USGS U.S. Geological Survey, Alaska Science Center

INDUSTRY Petroleum and related industry personnel

LOCAL Residents of coastal villages and homesteads

USFWS US Fish and Wildlife Service, Marine Mammals Management

USFWS-ADFG FWS and ADFG collaboration

Discovery_method

CONVENTIONAL Discovered during other USGS, FWS and ADFG polar bear field research efforts

FLIR Discovered with Forward-looking Infrared sensors

REPORT Reported to USGS from other individuals or agencies

SATELLITE Discovered through satellite telemetry

VHF_RADIO Discovered through very high frequency (VHF) telemetry

Confirmation

C

Denning confirmed by site visit or subsequent observation of female with dependent 

young

P

Evidence of denning from satellite-linked tags data but absence of site visit or subsequent observation of female with dependent young

Substrate

P Pack ice – floating and mobile sea ice

F Fast ice – sea ice attached to land and immobile

L Land

U Unknown substrate

Position_method

map Position assumed to have been estimated with a topographic map

aircraft

Position estimated with aircraft navigation systems (non-Global Positioning System 

[GPS])

Argos LC=

Position estimated from an Argos-radio tag attached to the polar bear, where LC=3, 2, 1, 

0, A, B, or Z

field gps Position estimated by GPS on site (field, including aircraft)

satellite gps Position estimated by GPS-equipped satellite-radio tag attached to the polar bear
Publishing support provided by the U.S. Geological Survey

Science Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

Director, Alaska Science Center

U.S. Geological Survey

4210 University Drive

Anchorage, Alaska 99508

https://www.usgs.gov/centers/asc/
Durner and others—Catalogue of Polar Bear (Ursus maritimus) Maternal Den Locations, Beaufort and Chukchi Seas, 1910–2018—Data Series 1121

ISSN 2327-638X (online)

https://doi.org/10.3133/ds1121 

Supersedes USGS Data Series 568