Arctic fox den identification and characteristics in northern Alaska

R. A. GARROTT Environmental Science Group, LS-6, MS-K495, Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM,

U.S.A. 87545

L. E. EBERHARDT Terrestrial Ecology Section, Pacijic Northwest Laboratory, P.O. Box 999, Richland, WA, U.S.A . 99352

AND

W. C. HANSON Dames and Moore, 800 Cordova Street, Suite 101, Anchorage, AK, U.S.A. 99501

Received May 15, 1982

GARROTT, R. A., L. E. EBERHARDT, and W. C. HANSON. 1983. Arctic fox den identification and characteristics in northern Alaska. Can. J. Zool. 61: 423-426.

Aerial surveys were an efficient and accurate means of locating arctic fox dens in northern Alaska, but some error was introduced through the misidentification of arctic ground squirrel dens. Forty-two arctic fox dens were identified within the 1700-km2 study area. Den sites were generally large, with complex burrow systems and possessed a distinctive plant community characterized by grasses and forbs, while adjacent areas were dominated by Dryas, lichens, and Carex. Since arctic fox den sites are important for reproduction, established dens should be identified and protected before major human activities are initiated in undisturbed areas in order to reduce the impacts of resource development on this species.

GARROTT, R. A., L. E. EBERHARDT et W. C. HANSON. 1983. Arctic fox den identification and characteristics in northern Alaska. Can. J. Zool. 61: 423-426.

Le survol s'est avCrC une mCthode efficace et exacte de reperage des terriers de renards arctiques dans le nord de 1' Alaska, mais il s'introduit un certain pourcentage d'erreur a cause de la rCsence de terriers d'Ccureuils de terre. Quarante-deux terriers de 4 renards actiques ont CtC repCrCs sur un territoire de 1700 km . Les sites ou se trouvent les terriers sont ordinairement de grandes dimensions et comportent des systkmes complexes de galeries; la communautC de plantes y est typique et se compose d'herbes et d'autres plantes herbacCes, alors que les rCgions adjacentes sont dominCes par des Dryas, des lichens et des Carex. Les sites de construction des terriers ont une grande importance pour la reproduction des renards arctiques. Avant d'amorcer des activitCs humaines de grande envergure dans les rCgions sauvages, il faudrait rep6rer et protCger les terriers dCja Ctablis de faqon h limiter l'impact du dCveloppement sur cette espece.

[Traduit par le journal]

Introduction Study area and methods The arctic fox (Alopex lagopus) is the principal fur

bearer of arctic Alaska and Canada. Recently, large areas of this species' habitat have undergone intensive exploration and development for petroleum resources. Arctic foxes have been shown in some regions to be relatively tolerant of human activities related to such development (Eberhardt et al. 1982), but physical alteration of habitat may destroy dens (Eberhardt 1977). Den sites are limited to localized areas where the permafrost is sufficiently deep and soil characteristics allow burrowing. At the onset of the breeding season in March and April, arctic foxes must reoccupy previously established dens because the ground is frozen, making excavation of new burrows impossible. Once estab- lished, dens may be used for several centuries before collapsing (Macpherson 1969); hence, existing den sites are critical to arctic fox reproduction. This study was part of a more comprehensive investigation of the ecological consequences of petroleum development in northern Alaska.

The 1700-km2 study area is located on the northern coast of Alaska at 70' 19' N, and includes the entire Colville River delta and adjacent areas on the east and west. This relatively undeveloped area is characterized by flat, treeless topography, tundra vegetation underlain by permafrost, a marshy terrain covered with a profusion of permanent and temporary lakes and ponds, and numerous river channels. The climate is severe with long, cold winters and short, cool summers. Expanding petroleum development activities from the Prudhoe Bay and Kuparuk oil fields are rapidly approaching the eastern bound- ary of the study area.

Arctic fox dens were located in the summers of 1975-1980 by searching the study area from a small aircraft (Piper Supercub) flying from 40 to 120 m above the ground at speeds of 80- 130 krn/h. When possible, dens located during aerial surveys were ground checked to verify their identity by the presence of large numbers of fox scats, prey remains, tracks, and(or) the presence of adult and juvenile arctic foxes. Preliminary surveys were conducted in 1975 and 1976 with extensive searches conducted in June 1977. Subsequent aerial surveys for determining den occupancy were conducted at various times during the summers of 1978-1980. During this

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424 CAN. J . ZOOL. VOL. 61. 1983

period new dens were occasionally located and incorporated into the study.

Den sites were numbered and their locations plotted on standard United States Geological Survey survey maps (1 : 63 360). The aspect of each den examined from the ground was determined using a hand-held compass; those dens having little or no slope were classified as open. Information on surface area (length x width), distance to water, and number of burrow entrances was also recorded.

Vegetative cover of each den was sampled by establishing four 8-m line transects oriented N-S , NE-SW , E-W , and SE-NW. The midpoint of each transect coincided with a stake placed in the center of the den. Groundcover was sampled by recording each plant found directly under 50 equidistant points along each transect. Vascular plants were identified according to Hulten (1968), and nonvascular plants were classified as moss or lichen. If no plants were found under a point, bare ground or litter were recorded. The abundance of upright woody shrubs ( 2 5 mm in diameter and 2 5 cm in height) was determined by randomly placing a 1-m2 hoop at a total of five points on the den. Area of coverage by shrubs was estimated to the nearest 5%.

The vegetative cover of a representative area adjacent to the den was also sampled to determine the effect of denning on vegetation. This area could not be randomly selected as dens were typically located on restricted topographical features such as sand dunes, pingos, or frost mounds surrounded by Carex marshes. Random selection would have resulted in sampling many areas that could not support dens. Because we wanted the physical characteristics (soil structure, exposure, and elevation) of adjacent plots to be similar to the den plots, we subjectively selected adjacent plots on the same topo- graphical feature as the den, usually 25 m from the den center.

A linear model using the percent dissimilarity index (Dyer 1978) was used to analyze for vegetative species dissimilarity to test the null hypothesis that ground cover of den plots was similar to that of adjacent plots. Because of programming limitations, only 27 genera and the categories of moss and lichen were used in the analysis. The 14 genera of vascular plants excluded were found in only trace quantities and usually only on a few plots.

Results and discussion Den identification

Aerial surveys were an efficient and accurate means of locating arctic fox dens, but some error was intro- duced through the misidentification of arctic ground squirrel (Spermophilus parryii) dens as arctic fox dens. Fifty-eight dens were located during aerial surveys, 49 of which were visited on the ground to verify identity. Forty-two of the 49 dens (86%) were arctic fox dens. All misidentified dens were large ground squirrel burrow complexes possessing many of the characteristics of an arctic fox den. The problem of misidentification was compounded by the fact that ground squirrels commonly occupied vacant arctic fox dens and were also sighted on occupied fox dens. The presence of a ground squirrel on a den was, therefore, not a good indicator of which

species originally excavated the den site or which was presently occupying the den.

Chesemore (1967) surveyed for arctic fox dens using large aircraft incapable of flying at slow speeds and had little success in locating dens. Macpherson ( 1969) relied almost exclusively on aircraft to locate dens, but he did not discuss any problems associated with misidentifica- tion. He stated that ground squirrel dens lacked the large rounded soil mounds which were common at arctic fox dens, and that ground squirrels excavated trenches through the mounds of recently abandoned arctic fox dens. Although mounds excavated by ground squirrels during this study were usually small, numerous ground squirrel burrow complexes possessed large soil mounds, sometimes exceeding 1.5 m in diameter. In addition, large, freshly excavated soil mounds were also observed on arctic fox dens that were occupied by ground squirrels. Trenching of soil mounds was not observed.

Den characteristics Sixty percent of the fox dens were not oriented in a

specific direction. Of those dens located on slopes, nine had southern exposures (four SW, three S, two SE), five possessed northerly aspects (one NW, two N, two NE), and one den was oriented to the west. Eberhardt (1977) also found the majority of the dens in his study area displayed an open exposure with the remainder of the dens tending toward a southern aspect. Most of the dens in both the Bolshezemelskaya tundra (Danilov 1968) and the Teshekpuk Lake areas (Chesemore 1969), however, displayed a southern aspect. Danilov (1 968) suggested that dens oriented southward have a more favorable microclimate because of the protection from the prevailing northeasterly winds. He also tested the hypothesis that more intensive warming of the soil occurs on slopes facing south but found only slight differences in soil temperature. Dens located on the top of topographical features may allow a more extensive burrow system to be excavated. Chesemore (1969) found that the depth to permafrost was greater at the tops of mounds than along the base and sides.

The position of arctic fox dens in relation to the nearest source of water ranged from 2 to 250m and averaged 48 m, which is less than the distances reported by Danilov (1968) and Eberhardt (1 977). The impor- tance of such information is questionable, since water is plentiful on the Arctic Coastal Plain of Alaska. Water is apparently not a problem for arctic foxes and the proximity of water to the dens is probably coincidental, or perhaps due to bettter drainage found on slopes near lakes and streams.

Vegetation surveys were conducted at 23 of the 42 known arctic fox dens. Dens located in inaccessible portions of the study area west of the Colville River were not included. Forty-one genera of vascular plants were

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GARROTT ET AL. 425

TABLE 1. The occurrence of moss, lichen, and the 11 most prevalent genera of plants located on arctic fox dens and on

areas adjacent to dens on the Colville River Delta, Alaska

No. of occurrences

On den Adjacent to den

Prevalent on den Poa Elymus Bromus Polemonium Arctagrostis Chrysanthemum Stellaria

Prevalent adjacent to den Dryas Lichens Carex Moss Salix Oxytropis

recorded in addition to mosses, lichens, litter, and bare ground. Results of the species dissimilarity analysis rejected the null hypothesis in favor of the alternative hypothesis, that the vegetative ground cover of the den plots was different from the cover of adjacent plots (P < 0.001).

Table 1 presents the total number of occurrences of the 13 most commonly recorded plants. A significant difference (P < 0.001) was noted for each species occurrence between den plots and adjacent plots. Den vegetation was characterized by grasses and three genera of forbs: Polemonium , Chrysanthemum, and Stellaria. Vegetation adjacent to dens was characterized by the genus Dryas, lichens, dry-land sedges and mosses, plants typical of the dry upland meadow community (Spetzman 1959).

A shrub layer was present on 20 of the 46 plots, 7 den and 13 adjacent plots, representing 15 den areas. Willow (Salix spp.) was the only shrub encountered with the exception of one specimen of the genus Vaccinium. Mean percent shrub cover varied from 1 to 43% for den plots and 1-21% for adjacent plots, with no distinct differences between plot types (P > 0.05).

Numerous authors in Russia (Dementyeff 1958; Danilov 1968), Canada (Macpherson 1969), and Alaska

The average number of burrow entrances for dens in the Colville River Delta area was 33 (range, 1-85) and surface area of dens averaged 256m2 (range, 1- 625 m2). These data contrast markedly with information reported by Danilov (1968) and Chesemore (1969). While dens in our study area were generally large with complex burrow systems, dens in the Teshekpuk Lake area were small and possessed simple burrow systems with a maximum of 26 entrances (Chesemore 1969). On the Bolshezemelskaya tundra, Danilov (1968) found den sites ranging from 5 to 25 m2, with 2 to 38 entrances.

Because of the importance of den sites for reproduc- tion, the limited areas capable of supporting burrows, and the long life of arctic fox dens we recommend that fox dens be identified before major development or exploration activities are initiated in areas where human disturbance has been minimal in the past. Arctic fox dens are conspicuous and can be easily identified by conducting aerial surveys. Surveys should include all drainage systems and topographic features capable of supporting burrows. The primary den characteristics that can be observed from aircraft are burrow entrances, soil mounds, and grass-forb dominated vegetation. Dens located from the air should be ground checked to verify their identity. The presence of fox scats, prey remains, and burrow entrances at least 15 cm in diameter indicate the den has been occupied by foxes. Evidence of occupation by foxes in many cases will not appear recent because dens may not be occupied for several consecutive years. Early identification and protection of established fox dens combined with regulations limiting or prohibiting harvesting of foxes in developed areas would reduce the impacts of resource development on arctic foxes. This view is supported by several studies documenting the ability of arctic foxes to occupy and successfully reproduce in areas undergoing intensive development (Eberhardt 1977; Fine 1980; Eberhardt et al. 1982).

Acknowledgements Research was conducted under United States Depart-

ment of Energy Contracts W-7405-ENG-36 and DE- AC06-76RLO 1830. We thank J. W. Helmericks for providing logistic support, W. M. Tzilkowski for computer assistance, J. L. Bengtson and D. A. Garrott for field assistance, and R. E. Fitzner for reviewing the manuscript.

(Chesemore 1969; ~berhard i 1977) have described the CHESEMORE, D. L. 1967. Ecology of the arctic fox in northern characteristic vegetation of arctic fox dens. All agree

and Alaska. M.S, thesis, University of Alaska, that den vegetation is dominated by grasses and a few forbs, in sharp contrast to the low tundra vegetation 1969. Den ecology of the arctic fox in northern typical of porous, well drained soils, and that this Alaska. Can. J. zool. 47: 121 -1 29. distinctive vegetation results from the denning activity DANILOV, D. N. 1968. Den sites of the arctic fox (Alopex of the foxes. lagopus) in the east part of the Bolshezemelskaya tundra.

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Problems of the North. No. 2 (Translation). National Research Council of Canada, Ottawa. pp. 225-229.

DEMENTYEFF, N. I. 1958. Biology of the arctic fox in the Bolshezemelskaya tundra. Russian Game Reports. Vol . 3 (Translation). Department of Northern Affairs and National Resources, Ottawa. pp. 166- 18 1.

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EBERHARDT, L. E., W. C. HANSON, J . L. BENGTSON, R. A. GARROTT, and E. E. HANSON. 1982. Arctic fox home range characteristics in an oil-development area. J . Wildl. Man- age. 46: 183-190.

EBERHARDT, W. 1977. The biology of arctic and red foxes on the North Slope. M.S. thesis, University of Alaska, Fairbanks.

FINE, H. 1980. Ecology of arctic foxes at Prudhoe Bay, Alaska. M.S. thesis, University of Alaska, Fairbanks.

HULTEN , E. 1968. Flora of Alaska and neighboring territories. Stanford University Press, Stanford, CA.

MACPHERSON, A. H. 1969. The dynamics of Canadian arctic fox populations. Can. Wildl. Serv. Rep. Ser. 8.

SPETEZMAN, L. A. 1959. Vegetation of the Arctic Slope of Alaska. Geological Survey Professional Paper 302-B . U . S . Government Printing Office, Washington.

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