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Central Arctic Caribou and Petroleum Development: Distributional, Nutritional, and Reproductive Implications


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We synthesize findings from cooperative research on effects of petroleum development on caribou (Rangifer tarandus granti) of the Central Arctic Herd (CAH). The CAH increased from about 6000 animals in 1978 to 23 000 in 1992, declined to 18 000 by 1995, and again increased to 27 000 by 2000. Net calf production was consistent with changes in herd size. In the Kuparuk Development Area (KDA), west of Prudhoe Bay, abundance of calving caribou was less than expected within 4 km of roads and declined exponentially with road density. With increasing infrastructure, high-density calving shifted from the KDA to inland areas with lower forage biomass. During July and early August, caribou were relatively unsuccessful in crossing road/pipeline corridors in the KDA, particularly when in large, insect-harassed aggregations; and both abundance and movements of females were lower in the oil field complex at Prudhoe Bay than in other areas along the Arctic coast. Female caribou exposed to petroleum development west of the Sagavanirktok River may have consumed less forage during the calving period and experienced lower energy balance during the midsummer insect season than those under disturbance-free conditions east of the river. The probable consequences were poorer body condition at breeding and lower parturition rates for western females than for eastern females (e.g., 1988 - 94: 64% vs. 83% parturient, respectively; p = 0.003), which depressed the productivity of the herd. Assessments of cumulative effects of petroleum development on caribou must incorporate the complex interactions with a variable natural environment.
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VOL. 58, NO. 1 (MARCH 2005) P. 1 9
Central Arctic Caribou and Petroleum Development:
Distributional, Nutritional, and Reproductive Implications
(Received 15 October 2002; accepted in revised form 11 May 2004)
ABSTRACT. We synthesize findings from cooperative research on effects of petroleum development on caribou (Rangifer
tarandus granti) of the Central Arctic Herd (CAH). The CAH increased from about 6000 animals in 1978 to 23000 in 1992,
declined to 18000 by 1995, and again increased to 27000 by 2000. Net calf production was consistent with changes in herd size.
In the Kuparuk Development Area (KDA), west of Prudhoe Bay, abundance of calving caribou was less than expected within
4 km of roads and declined exponentially with road density. With increasing infrastructure, high-density calving shifted from the
KDA to inland areas with lower forage biomass. During July and early August, caribou were relatively unsuccessful in crossing
road/pipeline corridors in the KDA, particularly when in large, insect-harassed aggregations; and both abundance and movements
of females were lower in the oil field complex at Prudhoe Bay than in other areas along the Arctic coast. Female caribou exposed
to petroleum development west of the Sagavanirktok River may have consumed less forage during the calving period and
experienced lower energy balance during the midsummer insect season than those under disturbance-free conditions east of the
river. The probable consequences were poorer body condition at breeding and lower parturition rates for western females than for
eastern females (e.g., 198894: 64% vs. 83% parturient, respectively; p = 0.003), which depressed the productivity of the herd.
Assessments of cumulative effects of petroleum development on caribou must incorporate the complex interactions with a variable
natural environment.
Key words: behavior, body condition, calving, cumulative effects, demography, fecundity, habitat, Rangifer
RÉSUMÉ. On a procédé à une synthèse des résultats de travaux de recherche coopérative concernant les effets de l’exploitation
pétrolière sur le caribou (Rangifer tarandus granti) formant la harde du centre de l’Arctique (HCA). La population de celle-ci est
passée de 6000 têtes en 1978 à 23000 en 1992, puis a diminué à 18000 en 1995 pour augmenter de nouveau à 27 000 en 2000.
La production nette des veaux allait de pair avec les changements dans la taille de la harde. Dans la zone de développement de
Kuparuk (KDA), située à l’ouest de Prudhoe Bay, l’abondance des caribous qui mettaient bas était inférieure à celle prévue dans
une bande de 4 km de part et d’autre des routes, et elle déclinait de façon exponentielle avec la densité routière. Avec une
augmentation des infrastructures, on assistait à un déplacement du vêlage à forte densité de la KDA vers des zones de l’intérieur
ayant une biomasse de fourrage moins importante. Durant juillet et au début d’août, il était assez rare que les caribous réussissent
à traverser les corridors routiers/pipeliniers dans la KDA, surtout lorsqu’ils formaient de vastes agrégations harcelées par les
insectes; l’abondance de même que les déplacements des femelles étaient en outre moindres au sein du complexe pétrolier de
Prudhoe Bay qu’à d’autres endroits situés le long du rivage arctique. Il est possible que les femelles qui étaient exposées à
l’exploitation pétrolière à l’ouest de la rivière Sagavanirktok aient consommé moins de fourrage au cours de la période de vêlage
et que, durant la saison des insectes au milieu de l’été, elles aient connu une balance énergétique inférieure à celle des femelles
vivant sans perturbations à l’est de la rivière. Les conséquences probables étaient un état corporel de qualité inférieure au moment
de l’accouplement, et des taux de parturition plus faibles pour les femelles situées à l’ouest que pour celles situées à l’est (p. ex.,
de 1988 à 1994: 64 % c. 83 % de parturientes respectivement: p = 0,003), faisant ainsi baisser la productivité de la harde. Les
évaluations des effets cumulatifs de l’exploitation pétrolière sur le caribou doivent intégrer les interactions complexes avec un
environnement naturel variable.
Mots clés: comportements, état corporel, vêlage, effets cumulatifs, démographie, fécondité, habitat, Rangifer
Traduit pour la revue Arctic par Nésida Loyer.
Alaska Department of Fish and Game, 1300 College Road, Fairbanks, Alaska 99701-1599, U.S.A.
Present address: Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska 99775, U.S.A.;
Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska 99775, U.S.A.
USGS Alaska Cooperative Fish and Wildlife Research Unit, University of Alaska Fairbanks, Fairbanks, Alaska 99775, U.S.A.
© The Arctic Institute of North America
2 • R.D. CAMERON et al.
From the mid-1970s through the mid-1980s, use of calving
and midsummer habitats by Central Arctic Herd (CAH)
caribou (Rangifer tarandus granti) declined near oil field
infrastructure on Alaska’s Arctic Coastal Plain (Cameron
et al., 1979; Cameron and Whitten, 1980; Smith and
Cameron, 1983; Whitten and Cameron, 1983a, 1985; Dau
and Cameron, 1986). With surface development continu-
ing to expand westward from the Prudhoe Bay oil field
complex (Fig. 1), concerns arose that the resultant cumu-
lative losses of habitat would eventually reduce productiv-
ity of the herd. Specifically, reduced access of adult females
to preferred foraging areas might adversely affect growth
and fattening (Elison et al., 1986; Clough et al., 1987), in
turn depressing calf production (Dauphiné, 1976; Tho-
mas, 1982; Reimers, 1983; White, 1983; Eloranta and
Nieminen, 1986; Lenvik et al., 1988; Thomas and Kiliaan,
1998) and calf survival (Haukioja and Salovaara, 1978;
Rognmo et al., 1983; Skogland, 1984; Eloranta and
Nieminen, 1986; Adamczewski et al., 1987).
Those concerns, though justified in theory, lacked em-
pirical support. With industrial development in Arctic
Alaska virtually unprecedented, there was little basis for
predicting the extent and duration of habitat loss, much
less the secondary short- and long-term effects on the well-
being of a particular caribou herd. Furthermore, despite a
general acceptance that body condition and fecundity of
females are functionally related for reindeer (R. t. tarandus)
and caribou, it seemed unlikely that any single model
would apply to all subspecies of Rangifer, or even within
a subspecies, to all geographic regions. We therefore
lacked a complete understanding of the behavioral re-
sponses of Arctic caribou to industrial development, the
manner in which access to various habitats might be
affected, and how changes in habitat use might translate
into effects on fecundity and herd growth.
Our studies had four objectives: 1) to estimate variation
in the size and productivity of the CAH; 2) to estimate
changes in the distribution and movements of CAH cari-
bou in relation to oil field development; 3) to estimate the
relationships between body condition and reproductive
FIG. 1. Roads and facilities in the Kuparuk Development Area (west of the Kuparuk River) and Prudhoe Bay oil field complex (east of the Kuparuk River), Alaska,
ca. 1990 (Cameron et al., 1995; reprinted with permission from Rangifer).
performance of female CAH caribou; and 4) to compare
the body condition and reproductive success of females
under disturbance-free conditions (i.e., east of the
Sagavanirktok River) with the status of those exposed to
petroleum-related development (i.e., west of the
Sagavanirktok River) (Fig. 1).
Status of the Central Arctic Herd
Photocensus results indicate net growth of the CAH
from 1978 through 2000 (Fig. 2). Within that long-term
trend, however, was a decrease from 1992 to 1995, which
coincided with calf production estimates at or below ap-
proximately 70%. Calf production was also relatively low
during 198991, suggesting that herd growth had deceler-
ated or ceased before the 1992 census. Otherwise, periods
of apparent growth were associated with productivity
estimates exceeding 70%.
Development-Related Changes in Distribution
Because the CAH is in contact with industrial develop-
ment from calving time through midsummer, our surveys
focused on those two intervals. The calving period is the
three-week interval beginning with the peak of calving,
i.e., after 50% of the calving has occurred (Russell et al.,
2002:31); for the CAH, this peak usually occurs in early
June (Cameron et al., 1993). The summer insect season
follows, generally extending from late June through early
August (White et al., 1975; Dau, 1986).
Changes in the distribution of calving caribou associ-
ated with the Kuparuk Development Area (KDA), west of
the Kuparuk River (Fig. 1), were quantified by means of
strip-transect surveys conducted from a helicopter. After
construction of a road system between Milne Point and the
Spine Road (Fig. 1), mean caribou abundance declined by
more than two-thirds within 2 km of roads and was less
than expected, overall, within 4 km, but nearly doubled
46 km from roads (Fig. 3). Before road construction,
caribou were found in a single, more or less continuous
concentration that encompassed the area where roads would
subsequently be built. After road construction, a bimodal
distribution was clearly apparent, with separate concentra-
tions to the west and east of the road (Fig. 4), indicating
avoidance of infrastructure by calving caribou.
These results suggest that roads spaced too closely will
depress calving activity within portions of an oil field
complex. In fact, relative abundance of caribou in the
heavily developed western portion of the KDA showed a
significant decline from 1979 through 1987, which was
independent of total abundance (Fig. 5). Such declines
FIG. 2. Photo-census estimates of the Central Arctic caribou herd, 19782000
(Whitten and Cameron, 1983b; Alaska Department of Fish and Game files) and
net calf production based on observations of radio-collared adult (i.e., sexually
mature) females from 10 June through 15 August (Alaska Department of Fish
and Game files). Note: Productivity data are not adjusted for differences in
sample sizes east and west of the Sagavanirktok River.
FIG. 3. Changes in mean density of calving caribou from the Central Arctic
Herd from 197881 (before road construction) to 1982 87 (after road
construction) at distances of 06 km (in 1 km intervals) from the Milne Point
road system, Kuparuk Development Area, Alaska (Cameron et al., 1992b;
reprinted with permission from Arctic).
4 • R.D. CAMERON et al.
apparently involve an exponential decrease in caribou
density with increasing road density (Fig. 6). The probable
consequence is reduced access to preferred foraging habi-
tats (Nellemann and Cameron, 1996, 1998).
Incremental redistribution and local habitat loss within
the KDA may have triggered changes on a regional scale.
Wolfe (2000) reported an inland shift of concentrated calving
activity away from the Milne Point area (Fig. 7), which
coincided with an increase in the density of infrastructure.
Ground observations within the KDA provided addi-
tional insights on changing distribution and movements.
During 197890, observations that caribou increasingly
avoided zones of intensive construction and production-
related activity, especially during the calving period (Smith
et al., 1994), corroborated data from strip-transect sur-
veys. Lower success in crossing road/pipeline corridors by
large, insect-harassed groups during summer (Smith and
Cameron, 1985; Curatolo and Murphy, 1986; Murphy and
Curatolo, 1987; Murphy, 1988) may have contributed to
relatively greater use of peripheral areas with less surface
development and human activity. Primary routes of sum-
mer movement have shifted to areas south of Oliktok Point
and along the Kuparuk River floodplain (Smith et al.,
An analysis of the summer distribution of radio-col-
lared females during 1980–93 (Cameron et al., 1995)
suggested that caribou use of the oil field region at Prudhoe
Bay had declined considerably from that noted by Child
FIG. 4. Changes in mean relative distribution of caribou from the Central Arctic
Herd in the Kuparuk Development Area, Alaska, during calving in 197981,
198286, and 198790. Each transect segment was 10.4 km
, or 0.9% of the
1150 km
surveyed. Only those segments with more than 0.9% of the total
caribou observed are shown. Gradations in line spacing depict caribou densities
as multiples of the base density derived from that percentage: wide spacing =
less than 3 × base; narrow spacing = 35 × base; solid = more than 5 × base
(Smith and Cameron, 1992; reprinted with permission).
FIG. 5. Histogram shows decline in abundance of calving caribou from the
Central Arctic Herd west of the Milne Point road system, Alaska, 1979–87
(Spearman’s Rank, p < 0.02). Abundance is expressed as a percentage of the
total numbers of caribou north of the Spine Road (see Fig. 1), shown in the line
graph below (Cameron et al., 1992b; reprinted with permission from Arctic).
(1973), and White et al. (1975) during the 1970s. Both
caribou abundance within the main industrial complex and
east-west caribou movements through that area were sig-
nificantly lower (p < 0.001) than in other areas occupied by
caribou along the Arctic coast. Conservative calculations
yielded an estimated 78% decrease in use by caribou and
a 90% decrease in their east-west movements (Cameron et
al., 1995), changes apparently in response to intensive
development of that region over the past three decades.
However, the occurrence of caribou that do use the com-
plex during summer is reportedly unrelated to distance
from infrastructure (Cronin et al., 1998).
Body Condition and Reproductive Performance
Reproductive success of caribou is highly correlated
with nutritional status. The probability of producing a calf
varies directly with both body weight and body fat content
of sexually mature females during the previous autumn
(Cameron et al., 1993, 2000; Cameron and Ver Hoef,
1994; Gerhart et al., 1997). In contrast, calving date and
perinatal survival are more closely related to maternal
weight shortly after parturition (i.e., estimated prepartum
body weight minus weight of fetal tissues) (Fig. 8). Thus,
the likelihood of conceiving is probably determined by
body condition at breeding, whereas parturition date and
calf survival may reflect maternal condition during late
In theory, these relationships link the nutritional conse-
quences of changes in distribution to the reproductive
success of caribou of the CAH. West of the Sagavanirktok
River, caribou had reduced access to preferred foraging
habitats near roads (Nellemann and Cameron, 1996) and
FIG. 6. Relationship between mean (SE) density of calving caribou from the
Central Arctic Herd and road density within preferred rugged terrain, Kuparuk
Development Area, Alaska, 198792. Different letters indicate a significant
difference (p < 0.05) (Nellemann and Cameron, 1998; reprinted with permission
from the Canadian Journal of Zoology).
FIG. 7. Shifts in concentrated caribou calving areas of the Central Arctic Herd
between the Colville and Canning rivers (note oil field infrastructure, Fig. 1),
Alaska, 198095 (adapted from Wolfe, 2000: Fig. 3).
6 • R.D. CAMERON et al.
FIG. 8. Logistic regressions of parturition rate, incidence of early calving (on
or before 7 June), and perinatal calf survival (> two days postpartum) on autumn
and summer body weights of female caribou, Central Arctic Herd, Alaska,
198791. Solid lines are significant at p < 0.05. The empirical percentages are
shown at arbitrary 10 kg intervals of body weight. Numbers in parentheses are
sample sizes. *The weight category 6070 kg includes one female weighing
57 kg (Cameron et al., 1993; reprinted with permission from the Canadian
Journal of Zoology).
FIG. 9. Mean (SE) body weights of lactating (n = 23) and nonlactating (n = 23)
female caribou in summer (July) and autumn (October), Central Arctic Herd,
Alaska, 1988–91. *Difference is significant at p < 0.001 (Cameron and White,
FIG. 10. Distributions of observed autumn (October) body weights for lactating
and nonlactating female caribou, Central Arctic Herd, Alaska, 1988–91. The
associated parturition rates are integrated estimates derived from the logistic
model (Fig. 8) (Cameron and White, 1996).
shifted their concentrated calving area into habitats with
lower plant biomass (p < 0.001) (Wolfe, 2000). In contrast,
forage biomass remained constant (p = 0.23) within con-
centrated calving areas east of the Sagavanirktok River,
where no development was present (Wolfe, 2000). Re-
peated use of lower-quality calving habitats may reduce
forage intake by females to the west. Likewise, impaired
summer movements between insect-relief habitat and in-
land feeding areas could depress energy balance (Smith,
1996) and, hence, rates of weight gain.
Indeed, several data sets suggest reduced nutritional
status and fecundity of radio-collared females exposed to
oil development west of the Sagavanirktok River. Esti-
mates of July and October body weights, over-summer
weight gain, the incidence of two pregnancies in succes-
sive years, and perinatal calf survival all tended to be
lower for females to the west than for those under distur-
bance-free conditions to the east, although individual
differences were not significant at the 95% confidence
level (Cameron et al., 1992a). In a more recent analysis of
data for 1988 94, however, the mean parturition rate of
females west of the Sagavanirktok River was 64% com-
pared with 83% for females to the east (p = 0.003, Table 1)
(Cameron, 1995). Corresponding frequencies of repro-
ductive pauses (Cameron, 1994; Cameron and Ver Hoef,
1994) were 36% to the west of the river (26 of 73 observa-
tions) and 19% to the east (12 of 64 observations) (p < 0.02,
t-test, ratio method), or approximately one pause every
three and five years, respectively (Cameron, 1995). With
the opening of the Badami production unit east of the
Sagavanirktok River in 1996, the undisturbed status of that
area was compromised, rendering further comparisons
The key constraint on reproduction is lactation: it ex-
acts a substantial cost on summer weight gain, which in
turn influences the probability of conceiving that autumn.
During 198891, weights of all lactating CAH females
sampled averaged 9 kg less than those of nonlactating
females (Fig. 9), resulting in a projected 28% reduction in
parturition rate (Fig. 10). Lower parturition rates of
females west of the Sagavanirktok River during 198894
(Table 1) may reflect a failure to compensate for the
metabolic burden of milk production (i.e., through in-
creased forage intake or reduced energy expenditure). The
result is consistently poorer condition in autumn and,
hence, more frequent reproductive pauses, which contrib-
ute to a decline in calf production of the herd (Fig. 2).
Yet the degree to which lactation constrains weight gain
does vary. An increase in net calf production during 1996
2000 (Fig. 2) suggests the prevalence of forage and insect
conditions that enhanced growth and fattening, despite the
demands of milk production and the presence of industrial
Anthropogenic effects on caribou must be identified and
assessed within the framework of a variable natural environ-
ment. Favorable foraging and insect conditions would attenu-
ate the consequences of disturbance-induced changes in the
quality of habitats occupied. Conversely, adverse conditions
would exacerbate those same types of consequences (e.g.,
NRC, 2003:114–115). Unless analyses are based on multi-
year observations of marked individuals and incorporate
comparative data on an undisturbed control or reference
group, conclusions will be equivocal at best. For example,
absent a valid baseline, net growth of the CAH (Fig. 2) is no
better evidence of compatibility with development than a net
decline would be evidence of a conflict.
The crucial consideration for the future of the CAH and
other Arctic caribou herds is whether changes in distribution
associated with surface development, by depressing repro-
duction or survival, will either retard an increase in herd size
or accelerate a decrease. Our data, in fact, indicate that
productivity can and will decline if the cumulative loss of
preferred habitat, when superimposed on natural forces, is
sufficient to compromise nutrition.
Base funding was provided by Federal Aid in Wildlife Restoration
and the Division of Wildlife Conservation, Alaska Department of
Fish and Game. Supplemental support was provided by the Alaska
Fish and Wildlife Research Center, U.S. Fish and Wildlife Service;
Division of Habitat and Division of Subsistence, Alaska Department
of Fish and Game; Institute of Arctic Biology, University of Alaska
Fairbanks; ARCO Alaska, Inc.; EXXON Co. U.S.A.; SOHIO
Petroleum Co.; CONOCO, Inc.; Continental Pipeline Co.; and the
Alaska Department of Transportation and Public Facilities.
For analytical advice and technical assistance, we thank M.M.
Billington, D.A. Borchert, K. Butters, G.M. Carroll, R.A. Caulfield,
J.R. Dau, R.A. DeLong, S.G. Fancy, R.K. Friedrich, K.L. Gerhart,
C.S. Gewin, H.N. Golden, R.G. Hunter, N. Ihlenfeldt, K. Jouppi,
E.A. Lenart, J.A.K. Maier, T.R. McCabe, L.A. McCarthy, L.M.
McManus, D.C. Miller, S. Pedersen, D.J. Reed, J.W. Schoen, M.D.
Smith, R.T. Shideler, P. Valkenburg, J.M. Ver Hoef, N.E. Walsh,
K.R. Whitten, J.F. Winters, and S.A. Wolfe. S.G. Fancy and two
anonymous reviewers offered helpful comments and suggestions.
An earlier version of this paper appeared as a section in a U.S.
Geological Survey technical report (Cameron et al., 2002).
We dedicate this review to the memory of Ronald M. Warbelow,
who died in 1995 after a long battle with cancer. Equally skilled at
the controls of a helicopter or a fixed-wing aircraft, Ron was
instrumental in the success of caribou capture and survey programs
in the late 1980s and early 1990s. His friendship and enthusiastic
participation will not be forgotten.
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% Parturient (n)
Year West East
1988 72.7 (11) 100.0 (8)
1989 53.8 (13) 77.8 (9)
1990 83.3 (12) 100.0 (7)
1991 45.5 (11) 75.0 (12)
1992 72.7 (11) 75.0 (12)
1993 55.6 (9) 62.5 (8)
1994 66.7 (6) 87.5 (8)
Mean parturition rate, %
± 5.0 82.5 ± 5.3
All sexually mature.
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... In addition to their importance for many ecological processes (Ballard et al. 1997, Stark et al. 2015, Heggenes et al. 2018, caribou are also central to food security and the cultural well-being of many indigenous groups across the circumpolar arctic (Wolfe and Walker 1987, Bjørklund 1990, Berkes et al. 1994. Caribou may respond to human development and activity with altered distribution and movement throughout their annual cycle (Johnson et al. 2005, Plante et al. 2018, Johnson et al. 2020), but appear most sensitive to human disturbance during the calving period when females with newborn calves may displace 4 km or more from infrastructure related to oil and gas development (Cameron et al. 2005, Johnson et al. 2020. ...
... Habitat values of pixels overlapping existing and simulated infrastructure were assigned a value of 0, indicating complete loss of calving habitat. Other pixels within 4 km of infrastructure had their value degraded according to the following equation for caribou displacement from infrastructure (Wilson et al. 2013, based on data from Cameron et al. 2005): w x ð Þ ¼ expðÀ2:974 þ 1:079  xÞ 1 þ expðÀ2:974 þ 1:079  xÞ where w(x) is the proportional reduction in use by calving caribou, and x is distance from infrastructure in kilometers. We then calculated the proportion of pixels of high-quality calving habitat lost after accounting for the effects of infrastructure (Wilson et al. 2013). ...
... Development-related habitat loss on arctic breeding grounds, especially under Alternative D, could compound other effects and has the potential to exacerbate population declines in sensitive species , Galbraith et al. 2014. Climate-related stressors such as rain-on-snow events and landscape-scale impacts have been well documented in caribou and reindeer (Vors and Boyce 2009, Joly et al. 2011, Forbes et al. 2016, Mallory and Boyce 2018, making undisturbed access to seasonal habitats key to maintaining individual body condition and overall herd productivity (Griffith et al. 2002, Cameron et al. 2005. ...
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Wildlife management often involves trade-offs between protecting species and allowing human activities and development. Ideally, these decisions are guided by scientific studies that quantify the impacts of proposed actions on the environment. However, critical information to assess impacts of proposed activities may be lacking, such as certainty in where actions will take place, which may hinder a robust impact assessment. To address this issue, we present the Development Impacts Analysis (DIA), which employs Monte Carlo simulation modeling to quantify the environmental consequences of proposed development scenarios, while accounting for uncertainty in the exact location of future development. We applied the DIA to five proposed oil leasing management scenarios under a revised management plan for the National Petroleum Reserve-Alaska. For each management scenario with differing levels of proposed development ("alternatives"), oil production pads and roads were randomly simulated in proportion to estimated undiscovered oil and following alternative-specific restrictions. We assessed habitat displacement for two caribou (Rangifer tarandus) herds, eight shorebird species, and black brant (Branta bernicla) based on reported responses to development, repeating the process 100 times for each alternative. Some habitat loss was reported for each proposed alternative, but the amount of impact varied by alternative and species. One caribou herd and most bird species indicated greatest effects in the alternative with the least restrictions on development and lesser impacts under more protective alternatives. Our results emphasized the importance of considering spatial variation in development effects and species-specific differences when evaluating management proposals. The DIA quantified potential impacts on a suite of species under proposed management alternatives, while accounting for uncertainty in where development will occur and providing confidence intervals on estimated impacts. This illustrates that uncertainty need not preclude management decisions about establishment of broad land use restrictions prior to submission of project-level proposals but can instead be explicitly incorporated into decision making. While no single management approach will likely benefit all species, use of tools such as the DIA allows managers to quantify trade-offs among species and pursue approaches that balance the needs of various taxa and other management objectives.
... Following construction of the Kuparuk and Milne Point oilfields in the western calving area, highdensity calving gradually shifted south and southwest of the Kuparuk oilfield (Murphy and Lawhead, 2000;Wolfe, 2000;Noel et al., 2004;Joly et al., 2006). This shift in calving distribution may have been a result of development, resulting in regional displacement from a previously used calving area (NRC, 2003;Cameron et al., 2005;Prichard et al., 2020a), although the calving distribution in the eastern area, where there is limited development, also shifted to the west and southwest in the last two decades (Arthur and Del Vecchio, 2009;Lenart, 2015). ...
... The principal summer range of the CAH is located between the Colville and Canning Rivers on the central Arctic Coastal Plain (Murphy and Lawhead, 2000;Cameron et al., 2005;Nicholson et al., 2016), a region that includes the Kuparuk, Milne Point, Prudhoe Bay, Endicott, Badami, and Point Thomson oilfields. Major construction activities began in the mid-1970s, when the CAH was estimated at 5000 caribou. ...
... The potential effects of displacing some maternal caribou from preferred calving areas depend on the availability and quality of alternative calving areas. If caribou are displaced to areas with lower forage quality or higher predator densities, displacement could result in lower calf survival or lower future productivity for cows (Griffith et al., 2002;NRC, 2003;Cameron et al., 2005). The cumulative effects of multiple roads within calving areas potentially could increase calving densities and thus decrease forage availability in alternative areas. ...
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Caribou are the most abundant large terrestrial mammals in Arctic Alaska, providing important cultural and subsistence resource values for local communities. As oil and gas development expands across the Arctic Coastal Plain of northern Alaska, understanding the potential impacts on caribou and improving associated mitigation measures are a crucial focus of applied research. One consistently observed impact in northern Alaska is displacement of maternal caribou within 2 – 5 km of active oilfield roads and gravel pads for a period of 2 – 3 weeks during and immediately after calving. A potential mitigation measure to address calving displacement is convoying of traffic to reduce traffic frequency and vehicle-related disturbance on roads in calving areas. We conducted frequent road and aerial surveys of caribou near two oilfield roads, one with convoying and one without, over a 3-year period during the precalving, calving, and postcalving periods to evaluate the effectiveness of traffic convoying. Road surveys indicated that caribou closer to the roads and groups with calves exhibited more frequent and stronger behavioural reactions in response to traffic, and that moderate or strong reactions to traffic, such as standing up and walking or running away, were more frequent near the road with convoying than near the road with unlimited traffic. Aerial survey results indicated some avoidance of areas up to at least 2 km from the road with convoying and 4 km from the road without convoying by caribou groups with calves. This relationship was present even after adjusting for other factors affecting distribution. This avoidance of roads by maternal caribou was limited to the calving period and was not evident during the precalving or postcalving periods. In addition, an inactive elevated terrestrial drilling platform was present on the calving grounds during one year, but we found no evidence of caribou avoidance of that structure during calving at our scale of analysis.
... During the past four decades, the barren-ground caribou (Rangifer tarandus granti) of the Central Arctic Herd (CAH) in Arctic Alaska have been studied extensively, particularly in summer because their calving grounds are located in oil and gas extraction areas near the Beaufort Sea coast; ( Fig. 1 ; [57][58][59][60][61][62][63][64][65]). The CAH population size was estimated at approximately 6000 animals in 1978 and grew steadily to its peak of 68,000 caribou in 2010 (with a slight decline during the early to mid-1990s), and was estimated to be roughly 30,000 animals in 2019 [60,61,66]. ...
... During the past four decades, the barren-ground caribou (Rangifer tarandus granti) of the Central Arctic Herd (CAH) in Arctic Alaska have been studied extensively, particularly in summer because their calving grounds are located in oil and gas extraction areas near the Beaufort Sea coast; ( Fig. 1 ; [57][58][59][60][61][62][63][64][65]). The CAH population size was estimated at approximately 6000 animals in 1978 and grew steadily to its peak of 68,000 caribou in 2010 (with a slight decline during the early to mid-1990s), and was estimated to be roughly 30,000 animals in 2019 [60,61,66]. From their annual gathering on the coastal calving grounds in summer, CAH caribou generally disperse during early fall (~end of Augustmid September) across the region extending from the Beaufort Sea coast, south to the Brooks Range (BR), and by October, they typically migrate further south to spend the winter either north or south of the Continental Divide (CD; running west to east along the crest of the BR; Fig. 1). ...
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Background Caribou and reindeer across the Arctic spend more than two thirds of their lives moving in snow. Yet snow-specific mechanisms driving their winter ecology and potentially influencing herd health and movement patterns are not well known. Integrative research coupling snow and wildlife sciences using observations, models, and wildlife tracking technologies can help fill this knowledge void. Methods Here, we quantified the effects of snow depth on caribou winter range selection and movement. We used location data of Central Arctic Herd (CAH) caribou in Arctic Alaska collected from 2014 to 2020 and spatially distributed and temporally evolving snow depth data produced by SnowModel. These landscape-scale (90 m), daily snow depth data reproduced the observed spatial snow-depth variability across typical areal extents occupied by a wintering caribou during a 24-h period. Results We found that fall snow depths encountered by the herd north of the Brooks Range exerted a strong influence on selection of two distinct winter range locations. In winters with relatively shallow fall snow depth (2016/17, 2018/19, and 2019/20), the majority of the CAH wintered on the tundra north of the Brooks Range mountains. In contrast, during the winters with relatively deep fall snow depth (2014/15, 2015/16, and 2017/18), the majority of the CAH caribou wintered in the mountainous boreal forest south of the Brooks Range. Long-term (19 winters; 2001–2020) monitoring of CAH caribou winter distributions confirmed this relationship. Additionally, snow depth affected movement and selection differently within these two habitats: in the mountainous boreal forest, caribou avoided areas with deeper snow, but when on the tundra, snow depth did not trigger significant deep-snow avoidance. In both wintering habitats, CAH caribou selected areas with higher lichen abundance, and they moved significantly slower when encountering deeper snow. Conclusions In general, our findings indicate that regional-scale selection of winter range is influenced by snow depth at or prior to fall migration. During winter, daily decision-making within the winter range is driven largely by snow depth. This integrative approach of coupling snow and wildlife observations with snow-evolution and caribou-movement modeling to quantify the multi-facetted effects of snow on wildlife ecology is applicable to caribou and reindeer herds throughout the Arctic.
... Declines are largely due to influences of industrial development that support increases in prey species such as white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) and moose (Alces alces (Linnaeus, 1758)) and their predators, which in turn elevate mortality of caribou (Festa-Bianchet et al. 2011;Apps et al. 2013;Hervieux et al. 2014;Serrouya et al. 2017;Fryxell et al. 2020). Influences of bottom-up factors such as nutrition for woodland caribou have infrequently been evaluated, but findings that nutrition, particularly summer nutrition, have important influences have emerged for far-north populations of caribou in Alaska (USA) (Post and Klein 1999;Cameron et al. 2005;Dale et al. 2008) and Canada Pachkowski et al. 2013;Schaefer and Mahoney 2013;Schaefer et al. 2016). Studies showed that adult female caribou often maintain or even increase body fat and experience only modest declines in lean mass over winter (Dauphiné 1976;Huot 1989;Chan-McLeod et al. 1999;Couturier et al. 2009), in turn also implicating nutritional resources in summer as a prominent influence on body condition of caribou (Couturier et al. 2009: 373). ...
... Our data suggest a hypothesis in need of stringent testing: that inadequate nutrition and nutritional condition in late spring through mid-summer are direct and indirect causes of mortality and that these linkages are widespread and numerically important in northern caribou ranges. Our results add to previous studies that identify nutritional limitations in summer for caribou Post and Klein 1999;Cameron et al. 2005;Dale et al. 2008;Post and Forchhammer 2008;Pachkowski et al. 2013;Schaefer and Mahoney 2013) and other ungulates (Hjeljord and Histol 1999;Cook et al. 2013Cook et al. , 2018Hurley et al. 2014;Rolandsen et al. 2017). ...
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Evaluating nutritional condition provides insights of nutritional influences on wildlife populations. We sampled three measures of condition — body fat, body mass, and loin thickness — of adult female caribou (Rangifer tarandus (Linnaeus, 1758)) in boreal settings in the Northwest Territories (NT), Canada, in December and March, 2016–2018, and in mountain and boreal settings in British Columbia (BC), Canada, in December and February, 2014–2015. We evaluated the effect of calf-rearing on condition in December, compared influences of summer–autumn versus winter on condition over winter, and developed an annual profile of nutritional condition with estimates from caribou dying in summer. Mean December body fat was 8.4% in females with calves and 11.4% in females without calves, demonstrating the influence of lactation on condition. Over winter, nutritional condition did not decline in northeastern BC and it declined slightly in NT: body fat by 0.55 percentage points, mass by 2.8 kg, and loin thickness did not change. Body fat peaked in December, changed little over winter, but declined to a minimum by early summer, temporally coinciding with elevated rates of adult female mortality. Consistent with those of other ungulate studies worldwide, our findings suggest a need to focus on nutritional limitations operating in late spring through early autumn.
... Once on their summer ranges, Arctic caribou often exhibit dynamic patterns of habitat use, shifting their distributions and habitat selection patterns every few weeks (Wilson et al., 2012; Bureau of Land Management [BLM], Bureau of Land Mangement, 2019a;Johnson et al., 2020;Severson et al., 2021;Figure 1). Researchers have assumed that their behavior is influenced, in part, by spatiotemporal variation in the nutritional value of forage (Cameron et al., 2005;Griffith et al., 2002), but the underlying drivers remain unknown. ...
... Movements of Arctic caribou to coastal habitat have been primarily attributed to seeking insect relief (White et al., 1975), but our work also highlights their importance in extending caribou access to high quality foraging areas. Coastal habitat used by caribou during the summer often overlaps with areas targeted for energy production (BLM, 2018(BLM, , 2019aWilson et al., 2012), and caribou have been observed to avoid industrial development Cameron et al., 2005;Johnson & Russell, 2014). For example, while the CAH will move through oil fields, Johnson et al. (2020) found that their use of habitat was less than expected within 5 km of energy development during the calving period, within 2 km during the post-calving period, and within 1 km during the mosquito period. ...
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Spatiotemporal variation in forage is a primary driver of ungulate behavior, yet little is known about the nutritional components they select, and how selection varies across the growing season with changes in forage quality and quantity. We addressed these uncertainties in barren-ground caribou (Rangifer tarandus), which experience their most important foraging opportunities during the short Arctic summer. Recent declines in Arctic caribou populations have raised concerns about the influence of climate change on summer foraging opportunities, given shifting vegetation conditions and insect harassment, and their potential effects on caribou body condition and demography. We examined Arctic caribou selection of summer forage by pairing locations from females in the Central Arctic Herd of Alaska with spatiotemporal predictions of biomass, digestible nitrogen (DN), and digestible energy (DE). We then assessed selection for these nutritional components across the growing season at landscape and patch scales, and determined whether foraging opportunities were constrained by insect harassment. During early summer, at the landscape scale, caribou selected for intermediate biomass and high DN and DE, following expectations of the forage maturation hypothesis. At the patch scale, however, caribou selected for high values of all forage components, particularly DN, suggesting that protein may be limiting. During late summer, after DN declined below the threshold for protein gain, caribou exhibited a switch at both spatial scales, selecting for higher biomass, likely enabling mass and fat deposition. Mosquito activity strongly altered caribou selection of forage and increased their movement rates, while oestrid fly activity had little influence. Our results demonstrate that early and late summer periods afford Arctic caribou distinct foraging opportunities, as they prioritize quality earlier in the summer and quantity later. Climate change may further constrain caribou access to DN as earlier, warmer Arctic summers may be associated with reduced DN and increased mosquito harassment.
... Evidence that ungulate populations are limited by nutrition either directly (e.g., impacts on reproduction, growth, or survival) or indirectly (e.g., susceptibility to predation, disease, or stochastic climate events) has been increasing. Particularly during summer and autumn, nutrition has been found to be inadequate for optimal performance in elk (Merrill 1987;Cook et al. 2013Cook et al. , 2016Cook et al. , 2018Johnson et al. 2019), mule deer (Peek et al. 2002;Hurley et al. 2014;Monteith et al. 2014), caribou (Chan-McLeod et al. 1999Cameron et al. 2005;Dale et al. 2008;Couturier et al. 2009;Denryter 2017), and moose (Hjeljord and Histol 1999;Ericsson et al. 2002;Herfindal et al. 2006aHerfindal et al. , 2006bMcArt et al. 2009;Rolandsen et al. 2017). Density dependence is often thought to be the main mechanism that accounts for severity of nutritional limitations in caribou (Caughley 1976(Caughley , 1970Couturier et al. 1990;Crête and Huot 1993;Vucetich and Peterson 2004), but recent studies suggest density-independent pathways also commonly influence nutritional status of large ungulate populations (Crête and Courtois 1997;DeYoung et al. 2008DeYoung et al. , 2019Cook et al. 2016). ...
... Nutritional condition data has also been used to predict population trends (e.g., Bishop et al. 2009;Monteith et al. 2014;Oates 2016;Stephenson et al. 2020), animal performance (Keech et al. 2000;Crouse 2003;Cook et al. 2004;Tollefson et al. 2010;Newby and DeCesare 2020), and more recently as a validation tool when developing broad-scale foodscape maps ). At a time when an abundance of research has documented nutritional limitations in caribou populations (Chan-McLeod et al. 1999;Cameron et al. 2005;Dale et al. 2008;Couturier et al. 2009;Denryter 2017) and climate change impacts to forage composition, quality, and quantity (Cornelissen et al. 2001;Lenart et al. 2002; Mallory and Boyce 2018), the importance of understanding the role of nutrition on populations is continuing to increase. ...
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Body composition studies are critical for evaluating the accuracy of nutritional condition indices for predicting body components. We evaluated >40 indices of nutritional condition for caribou (Rangifer tarandus (Linnaeus, 1758)) using 29 female caribou captured from three populations in Alaska (USA) that ranged in condition from 2.3% to 11.2% ingesta-free body fat (IFBF) and 6 captive female caribou that ranged in condition from 8.1% to 26.0% IFBF. Estimates of body fat, protein, and gross energy were regressed against each index of nutritional condition. Generally, indices with linear or slightly curvilinear relations to body fat and those based on multiple fat depots were the most accurate in predicting nutritional condition and the most useful over the full range of nutritional condition. A scaledLIVINDEX (a combination of subcutaneous fat thickness and a condition score), CONINDEX (a combination of kidney fat and marrow fat), and a subset of the Kistner score (pericardium and kidneys only) had the strongest relationship with body fat (r ² > 0.86) and were useful over the entire range of nutritional condition. If used properly and with adequate training, indices of nutritional condition can be a critical tool for understanding the severity and seasonality of nutritional limitations in wild caribou populations.
... Recent plans to produce oil in the 1002 Area of ANWR (BLM, 2019) have raised concerns about the loss of habitat and connectivity within the PCH early summer range, given that caribou tend to avoid industrial development, particularly during the calving season (Cameron et al., 2005;Johnson et al., 2020). We found that most of the projected future increases in suitable habitat in Alaska occurred within the 1002 Area (Table 1; (Cameron et al., 2005), coastal plain habitat for the PCH is already constrained to a narrow band between the Arctic Ocean and the Brooks Range (Figure 1). ...
... Recent plans to produce oil in the 1002 Area of ANWR (BLM, 2019) have raised concerns about the loss of habitat and connectivity within the PCH early summer range, given that caribou tend to avoid industrial development, particularly during the calving season (Cameron et al., 2005;Johnson et al., 2020). We found that most of the projected future increases in suitable habitat in Alaska occurred within the 1002 Area (Table 1; (Cameron et al., 2005), coastal plain habitat for the PCH is already constrained to a narrow band between the Arctic Ocean and the Brooks Range (Figure 1). As a result, there are limited options for displacement, which are likely to be further constrained in the future by the availability of preferred habitat under advancing phenology. ...
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Annual variation in phenology can have profound effects on the behavior of animals. As climate change advances spring phenology in ecosystems around the globe, it is becoming increasingly important to understand how animals respond to variation in the timing of seasonal events and how their responses may shift in the future. We investigated the influence of spring phenology on the behavior of migratory, barren‐ground caribou (Rangifer tarandus), a species that has evolved to cope with short Arctic summers. Specifically, we examined the effect of spring snowmelt and vegetation growth on the current and potential future space‐use patterns of the Porcupine Caribou Herd (PCH), which exhibits large, inter‐annual shifts in their calving and post‐calving distributions across the U.S.‐Canadian border. We quantified PCH selection for snowmelt and vegetation phenology using machine learning models, determined how selection resulted in annual shifts in space‐use, and then projected future distributions based on climate‐driven phenology models. Caribou exhibited strong, scale‐dependent selection for both snowmelt and vegetation growth. During the calving season, caribou selected areas at finer scales where the snow had melted and vegetation was greening, but within broader landscapes that were still brown or snow covered. During the post‐calving season, they selected vegetation with intermediate biomass expected to have high forage quality. Annual variation in spring phenology predicted major shifts in PCH space‐use. In years with early spring phenology, PCH predominately used habitat in Alaska, while in years with late phenology, they spent more time in Yukon. Future climate conditions were projected to advance spring phenology, shifting PCH calving and post‐calving distributions further west into Alaska. Our results demonstrate that caribou selection for habitat in specific phenological stages drive dramatic shifts in annual space‐use patterns, and will likely affect future distributions, underscoring the importance of maintaining sufficient suitable habitat to allow for behavioral plasticity.
... The overall effect is a gradual reduction in population productivity that increases with increasing nutritional inadequacy, ultimately influencing population growth rates (Crête and Huot 1993, Monteith et al. 2014, Stephenson et al. 2020). The preponderance of information for our study area implicates nutrition as a potential limiting factor for caribou populations (Kelly 2020, Cook et al. 2021a, Heard and Zimmerman 2021, as it is elsewhere in North America (Crête and Huot 1993, Post and Klein 1999, Cameron et al. 2005, Dale et al. 2008, Schaefer et al. 2016. Although nutritional limitations on caribou generally are thought to be density-dependent Huot 1993, Schaefer et al. 2016), our findings, coupled with low population densities of caribou in our study area, suggest nutrition may limit ungulates regardless of density (DeYoung et al. 2008(DeYoung et al. , 2019Cook et al. 2016), including in the boreal forests of Canada (Crête and Courtois 1997). ...
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Populations of woodland caribou (Rangifer tarandus caribou) are declining throughout their range and many are at risk of extirpation, yet the role of nutrition in these declines remains poorly understood, in part owing to a lack of information about available nutritional resources during summer. We quantified rates of intake of digestible protein and digestible energy by tame caribou foraging in temporary enclosures in the predominant plant communities of northeastern British Columbia, Canada, during summer–autumn and compared intake rates to daily requirements for protein and energy during lactation. We tested hypotheses related to the nutritional adequacy of the environment to support nutritional requirements during lactation (with and without replenishment of body reserves) and simulated scenarios of foraging by caribou in these plant communities to better understand how wild caribou could meet nutritional demands on these landscapes. Nutritional resources varied among plant communities across seasonal, ecological, and successional gradients; digestible energy intake per minute and per day were significantly greater in younger than older forests; dietary digestible energy and per‐minute and daily intake of digestible protein were greater, though not significantly so, in younger than older forests; and dietary digestible protein was greater in older than younger forests, though differences were not significant. Tame caribou were unable to satisfy protein and energy requirements during lactation, even without replenishment of body reserves, at most sites sampled. Further, foraging simulations suggested widespread nutritional inadequacies on ranges of wild caribou. Selection for habitats offering the best nutrition may mitigate some nutritional inadequacies, but given low availability of vegetation communities with high nutritional value, performance (e.g., calf production, growth, replenishment of body fat and protein) of caribou may be depressed at levels of nutrition documented herein. Our results, coupled with recent measurements of body fat of wild caribou in northeastern British Columbia, refute the hypothesis that the nutritional environment available to caribou during summer in northeastern British Columbia is adequate to fully support nutritional demands of lactating caribou, which has implications to productivity of caribou populations, recovery, and conservation. Nutritional resources available to caribou in northeastern British Columbia, Canada, during summer–autumn 2013–2015 were variable and largely inadequate to support nutritional requirements during lactation and for replenishment of body protein and fat reserves, thereby potentially constraining individual performance with implications to population productivity. Critical habitat designations corresponded poorly with nutritional value of caribou habitats in summer and early autumn.
Dust produced from mining has the potential to reduce plant cover, alter plant communities, and increase metal concentrations in vegetation, changes that may affect the amount, type, and quality of forage for barren-ground caribou (Rangifer tarandus groenlandicus). We quantified dust deposition from Diavik Diamond Mine (NWT, Canada) and investigated the changes on forage quality, type, and quantity for caribou. From 2002 to 2016, dust deposition was measured and vegetation cover and richness were assessed in permanent plots established adjacent to the mine and in reference areas 1 to 6 km from the mine. Lichen was collected from areas up to 100 km from the mine to determine metal concentrations. Dust deposition rapidly decreased within 4 km of the mine. Plant communities adjacent to the mine (within 500 m) had disproportionately increased cover of vascular plants and decreased bryophyte and lichen cover. Lichen sampled within 4 km from the mine had greater metal concentrations than those sampled farther afield. Concentrations of Al in lichen collected within 40 km of the mine exceeded safe exposure limits for consumption, assuming lichen comprised 100% of caribou diet. We conclude that dust deposition from mining is altering adjacent vegetation communities but that such changes to forage are unlikely to cause negative effects to caribou due to reduced lichen intake in summer and autumn, their migratory nature, and avoidance of mine-influenced areas. However, minimization and reclamation of mine-related disturbances will be important for maintaining sufficient quality forage and available habitat or space in caribou ranges. This article is protected by copyright. All rights reserved.
The Central Arctic caribou Rangifer tarandus granti herd (CAH) ranges on Alaska's Arctic Slope in the vicinity of the Trans- Alaska Pipeline Corridor and Prudhoe Bay Oilfield. In 1975 the CAH was identified as a distinct subpopulation. By 1978, the herd numbered c.4620 adults; the adult sex ratio was unusually high-a minimum of 1 bull per cow. A census conducted in 1981 indicated continued herd growth to c.6660 adults, with a decline in the adult sex ratio to c.80 bulls/100 cows. Yearling recruitment averaged 22% between 1978-1981. Actual herd growth was c.13% per year, implying an annual adult loss of 9%. -from Authors
Barren-ground caribou Rangifer tarandus granti of the Central Arctic Herd were surveyed from the road network of the oilfield complex near Prudhoe Bay, Alaska. Data on locally depressed calf percentages complement previous findings that females with young calves tend to avoid the Trans-Alaska Pipeline Corridor and indicate greater effects in areas of industrial activity. -from Authors
Resighting patterns corroborate the existence of a distinct Central Arctic Caribou Herd. The cow/calf segment of the herd appeared to avoid disturbed areas more so than did bulls. The heavily developed Prudhoe Oilfield was an effective barrier to both bulls and cows.-from Authors
Parturition status of 53 radiocollared, female caribou (Rangifer tarandus granti) of the central Arctic herd was determined through repeated observations by fixed-wing aircraft during 2-5 periods of parturition. The overall frequency of reproductive pauses for females that were initially parturient, or previously confirmed to be parturient, was 24% (ca. once every 4 years). Most pauses preceded (78%) and followed (87%) parturition events. Periodic infertility, as a response to nutritional stress, may enhance long-term reproductive performance in caribou and other ungulates.
Aerial surveys were conducted annually in June 1978-87 near Prudhoe Bay, Alaska, to determine changes in the distribution of calving caribou (Rangifer tarandus granfi) that accompanied petroleum-related development. With construction of an oil field access road through a calving concentration area, mean caribou density (no./km2) decreased from 1.41 to 0.31 (P = 0.05) within 1 km and increased from 1.41 to 4.53 (P = 0.04) 5- 6 km from the road. Concurrently, relative caribou use of the adjacent area declined (P < 0.02), apparently in response to increasing surface develop- ment. We suggest that perturbed distribution associated with roads reduced the capacity of the nearby area to sustain parturient females and that insufficient spacing of roads may have depressed overall calving activity. Use of traditional calving grounds and of certain areas therein appears to favor calf survival, principally through lower predation risk and improved foraging conditions. Given the possible loss of those habitats through dis- placement and the crucial importance of the reproductive process, a cautious approach to petroleum development on the Arctic Slope is warranted.
We investigated changes in distribution and terrain use of calving barren-ground caribou (Rangifer tarandus granti) with increasing density of roads in the Kuparuk Development Area, an oil-field region near Prudhoe Bay, Alaska. In June of 1987-1992, caribou density, as determined by aerial surveys, was inversely related to road density, declining by 63% at >0.0-0.3 km road/km(2) and by 86% at >0.6-0.9 km road/km(2). The latter road density virtually excluded cow-calf pairs. Effects of avoidance were most apparent in preferred rugged terrain, comprising important habitats for foraging during the calving period. Our results show that (i) females and calves are far more sensitive to surface development than adult males and yearlings, (ii) the greatest incremental impacts are attributable to initial construction of roads and related facilities, and (iii) the extent of avoidance greatly exceeds the physical "footprint" of an oil-field complex. A disproportionate reduction in use of foraging habitats within the Kuparuk Development Area, combined with decreasing tolerance of the expanding industrial complex, may explain the recent displacement of some calving activity to areas farther inland, and, in part, lower fecundity. Possible consequences include heightened competition for forage, increased risk of predation, and lower productivity of the herd.
Twelve collections of mature female caribou and calves (Rangifer tarandus groenlandicus) were conducted between June 1982 and June 1984 on Coats Island, Northwest Territories, Canada, to study seasonal changes in body composition in this winter mortality limited population. Mature females depleted reserves of dissectible fat and muscle considerably during both winters of the study, particularly the second, when nearly all dissectible fat and 32% of estimated fall muscle mass were lost. Recovery of fat and muscle was rapid during the two summers, because of good quality forage and little environmental disturbance. Lactation appeared to slow fattening in early summer 1983, but by October females achieved fatness similar to that in 1982, when a majority of females in summer and fall were nonlactating. Low rumen fill and consistently high fat and muscle levels in fall 1982 and 1983 suggested that mature females then approached "set points" in body fat and muscle content. Calves grew rapidly in summer; most of this growth was lean tissue, and their losses of body fat and muscle were severe during winter. Mature females and calves increased rumen fill substantially over winter to compensate for highly fibrous food. This made total body weight a much poorer predictor of condition than carcass weight. The liver, kidneys, and empty rumen were heaviest in summer in response to high forage quality. Poor condition of females was associated with light fetuses in May 1984.
Insect harassment significantly affect Rangifer tarandus granti behavior by decreasing time spent feeding and lying and by increasing locomotion. Effects of oilfield disturbance on behavior were most pronounced when insects were absent, suggesting that disturbance and insects did not have a substantial additive effect on behavior. When insects were absent, caribou within 600 m of an elevated pipeline and road with traffic, and within 300 m of a pipeline and road without traffic, had significantly different activity budgets than undisturbed caribou; disturbance effects were significantly greater in the site with traffic. Time spent lying and running and movement rates were the best indicators of oilfield disturbance, whereas time spent feeding was not affected. Cow-calf-dominated groups and groups >10 animals reacted to lower levels of disturbance than other group types, but all group types reacted similarly to high levels of disturbance. Separation of elevated pipelines from heavily traveled roads is recommended as a means of minimizing disruption of caribou behavior and movements.-from Authors