2007 NORTHEASTERN NATURALIST 14(4):571–588
Ecology and Habitat Selection of a Woodland Caribou
Population in West-central Manitoba, Canada
Juha M. Metsaranta1,2,* and Frank F. Mallory3
Abstract - This study examines the ecology of Rangifer tarandus caribou (woodland
caribou) in the Naosap range in west-central Manitoba, Canada. This population
is considered to be of high conservation concern because of potential resourcedevelopment
impacts; therefore, baseline data are required to guide and evaluate the
management of this species in this area. Radio-telemetry data were collected every
two weeks from February 1998 to April 2001 and used in combination with forestinventory
data to evaluate habitat selection, site fi delity, movement, and grouping
patterns. In both summer and winter, selected habitats were mature upland spruce
and pine forests, as well as treed muskeg. Hardwood forests were least selected at
all scales. Mature coniferous forest was preferred over immature coniferous forests
in a pair-wise comparison in winter, but not in summer. Home-range sizes were
within expected ranges of variation. Animals used distinct areas in summer and
winter, showing broad fi delity to seasonal ranges. However, small shifts in the core
areas were observed, particularly in winter. Movement rates and grouping behavior
were typical of other caribou. Habitats used in winter were common in the study
area, but the ability of the animals to disperse to alternate winter areas is not known.
Management efforts could focus on protecting known calving and winter-use areas,
and regenerating coniferous forests after logging, which is consistent with regional
forest-management objectives.
Introduction
This study investigated the ecology of Rangifer tarandus caribou
Gmelin (woodland caribou) in an area known as the Naosap caribou range
in west-central Manitoba, Canada (Fig. 1). This population is presently
considered to be of high conservation concern because of potential resource-
development impacts (Manitoba Conservation 2005). The purpose
of this study is to describe the ecological characteristics of this species in
this region because baseline data are required to guide and evaluate the
management of this species in this area. These data are currently lacking,
as research in the province has either historically been focused on
populations located elsewhere (Brown et al. 2000, Darby and Pruitt 1984,
Schaeffer and Pruitt 1991, Stardom 1975) or needs to be updated from
older studies in the region (Benoit 1996, Shoesmith and Storey 1977),
and thus needs to be collected in order to examine the effectiveness of
mitigation plans (Tolko Industries 1999). The study has three specific
1Department of Renewable Resources, University of Alberta, 751 General Services
Building, Edmonton, AB, Canada T6G 2H1. 2Current address - Canadian Forest
Servie, Pacifi c Forestry Centre, 506 West Burnside Road, Victori, BC, Canada, V8Z
1M5. 3Department of Biology, Laurentian University, 935 Ramsey Lake Road, Sudbury,
ON, Canada P3E 2C6. *Corresponding author - jmetsara@pfc.nrcan.gc.ca
572 Northeastern Naturalist Vol. 14, No. 4
objectives. The first is to determine and describe habitat-selection patterns
of this population at two spatial scales. The second is to describe the
ecology and general behavior of this population by assessing site fidelity
and describing home-range sizes, annual movement cycles, and grouping
behavior. The third is to discuss the implications of these observations to
caribou persistence in the study area.
For caribou, predator avoidance is the most important limiting factor at
larger spatial scales, and forage availability is the most important at smaller
spatial scales (Bergerud et al. 1990, Rettie and Messier 2000). Disturbances
can change both of these factors. Fire reduces lichen abundance and increases
accumulations of snow and deadfall, reducing forage availability
(Schaeffer and Pruitt 1991) or impeding movement (Metsaranta et al. 2003).
Forest-management practices may favor deciduous species, increasing forage
availability for other ungulates (Carleton and MacClennan 1994, Strong
and Gates 2006) or creating habitat unsuitable for caribou (Rettie and
Messier 2000). This can also increase populations of Alces alces L. (moose),
and consequently Canis lupus L. (wolves) (Bergerud and Elliot 1986, Seip
1992), which is detrimental to woodland caribou through changes to the
moose-wolf-caribou predator-prey dynamic.
In spring and summer, female woodland caribou with calves are solitary
and dispersed or spaced out in predator-free habitats like islands and
shorelines (Bergerud et al. 1990), or in the absence of these features, at
low densities over large areas (Bergerud 1996, Stuart-Smith et al. 1997).
Caribou aggregate in fall, and are found in small groups in winter (Brown
et al. 2000, Fuller and Keith 1981, Rettie and Messier 2001, Stuart-Smith et
al. 1997). Home ranges are larger in fall and winter than in spring and summer
(e.g., Mahoney and Virgil 2003, Rettie and Messier 2001, Stuart-Smith
et al. 1997). In some populations, individuals use non-overlapping seasonal
ranges (e.g., Bergerud et al. 1990, Cumming and Beange 1987), and in others
seasonal ranges overlap signifi cantly (Ouellet et al. 1996, Poole et al. 2000,
Figure 1. Location of the study area in west-central Manitoba, Canada.
2007 J.M. Metsaranta and F.F. Mallory 573
Stuart-Smith et al. 1997). Caribou show inter-year fi delity to calving sites,
and make shifts in the areas that they use each winter (e.g., Schaeffer et al.
2000, Wittmer et al. 2006), though these areas can be broadly similar (e.g.,
Cumming and Beange 1987).
Study Area
The study area is in west-central Manitoba, Canada, northeast of the
towns of Flin Flon and The Pas (Fig. 1). It is intersected by the boundary
of the Churchill River upland ecoregion of the boreal shield ecozone to the
north and the mid-boreal lowland ecoregion of the boreal plains ecozone to
the south. The boreal shield consists of interspersed uplands and lowlands
with bedrock outcrops, lakes, and low topographic relief. In contrast, the
boreal plains are topographically level to gently rolling, consisting of lacustrine
or organic parent materials. Tree species include Picea mariana (Mill.)
Britt. (black spruce), Picea glauca (Moench) Voss (white spruce), Pinus
banksiana Lamb. (jack pine), Larix laricina (DuRoi) (tamarack), Populus
tremuloides Michx. (trembling aspen), and Betula papyrifera Marsh. (white
birch) The climate is continental. Mean daily temperatures range from 17.7
ºC in July to -21.4 ºC in January. Mean annual rainfall and snowfall range
from 323.3 mm and 170.2 cm, respectively, in The Pas to 345.3 mm and
143.9 cm, respectively, in Flin Flon. Snow is present from mid-November
to early April, with maximum depths in January and February. Highway and
rail transportation corridors, forestry road development, hydro transmission
lines, and habitat disturbance from logging or forest fi res all potentially
affect this population. Forest management began in the early 1970s. Fires
occur naturally and are currently suppressed. A large part of the range burned
during a major fi re year in 1989 (Hirsch 1991).
Methods
Data collection
Radio-telemetry. Radio-telemetry data were collected from February of
1998 to April of 2001. Animals were captured by net gunning and outfi tted
with standard VHF radio collars (Lotek Wireless Inc, Newmarket, ON,
Canada). Between 14 and 25 female woodland caribou were located every
two weeks using standard aerial radio-tracking methods. Positions were
recorded by marking the location of the animal on aerial-photo mosaics and
by recording the latitude and longitude of the position using a GPS receiver.
Actual sightings occurred in 32% of cases, with sightings being more common
in winter (52%) than in summer (13%). A database of locations was
created using ArcView GIS (ESRI, Redlands, CA). Most locations were
manually digitized by comparing features on the aerial photo mosaics with
those on a Forest Resource Inventory (FRI) database displayed on screen.
Remaining locations were generated from the GPS co-ordinates recorded. A
total of 1358 locations were obtained.
574 Northeastern Naturalist Vol. 14, No. 4
Habitat data. Habitat data were obtained from the Manitoba FRI. A high
degree of correspondence between FRI’s and habitat characteristics important
to woodland caribou has previously been shown (Rettie et al. 1997).
Here, combinations of FRI components were aggregated into 12 habitat
types, based upon vegetative associations in the study area (Table 1). Areas
disturbed by fi re or logging were classifi ed as immature hardwood or immature
conifer, depending on the regeneration present. The FRI components
used to classify stands into each of the habitat types are described in Metsaranta
(2002). The FRI data were updated from aerial photography obtained
in either 1982–83 or 1987–88. Individual stands were updated to account for
events occurring before the end of 1998.
Statistical analyses
Habitat selection. Habitat selection was analyzed at two seasonal periods
(winter and summer) and two spatial scales (second- and third-order
selection Johnson 1980). Seasons were defi ned as October 16th to April
15th (winter) and April 16th to October 15th (summer), based on movement
patterns and the presence of snow cover. Years began on April 16th of one
year and ended on April 15th of the following year. Three annual periods
(1998, 1999, and 2000) were available for analysis. Habitat-selection patterns
could be assessed for 23 animals in summer and 22 in winter. At the
second-order (study-area) scale, availability was defi ned as the outermost
boundary of a combination of the 100% minimum convex polygon (MCP)
and 95% isopleth of the fi xed-kernel home range for all locations. Use was
defi ned by the seasonal 50% isopleth of the fi xed-kernel home range for
individual animals. At the third-order (home-range) scale, availability was
defi ned as the outer boundary of the 100% MCP home range for all telemetry
locations for an individual animal. To account for habitat-dependant bias
on location precision (Rettie and McLoughlin 1999), use was defi ned as a
Table 1. Habitat types available to woodland caribou in the Naosap range in west-central
Manitoba
Habitat type Total area (km2) Proportion of study area (%)
UCP (upland conifer pine) 420.7 9.3
UCS (upland conifer spruce/fi r) 498.8 11.0
OUC (open upland conifer) 54.5 1.2
IC (immature conifer) 667.6 14.7
OW (open wetland) 274.3 6.0
UH (upland hardwood) 966.8 2.1
OUH (open upland hardwood) 100.0 0.2
IH (immature hardwood) 542.2 1.2
LC (lowland conifer) 303.4 6.7
W (water) 760.1 16.7
TM (treed muskeg) 1385.8 30.5
NV (non-vegetated) 15.8 0.04
Total 4542.2 100.0
2007 J.M. Metsaranta and F.F. Mallory 575
circular buffer of radius 350 m in summer and 710 m in winter. These were
the mean daily movement rates of all animals in each season.
Habitat-selection patterns were determined using the compositional
analysis of log-ranks method (Aebischer et al. 1993). Habitats without any
use were replaced by 0.001, a value smaller than any other value in the dataset
(Aebischer et al. 1993). Third-order habitat selection was fi rst examined
by year to see if annual differences existed in habitat-type rankings. Using a
Wilcoxon sign-rank test, no signifi cant difference was found (see Results),
so data were pooled among years for all further analyses.
Site fi delity. Fixed-kernel home-range estimates were calculated at four
probability isopleths (95%, 75%, 50%, and 25%), and four combinations
of years and seasons (summer 1999 and 2000, and winter 1999 and 2000).
Home ranges could be calculated for n = 21 animals in both years. The number
of data points used to calculate the home ranges was low (mean = 12,
range 9 to 17), but these calculations were focused on assessing site fi delity,
and not accurate and precise home-range size estimation. To determine fi delity,
the intersection of the resulting vector polygons for each season or for
each year at each probability isopleth was calculated in ArcView. From this
spatial intersection, the Dice similarity coeffi cient (Dice 1945) was calculated
as:
2 (Pa∩Pb)
2 (Pa∩Pb) + Pa∉ Pb + Pb ∉ Pa
Where Pa ∩ Pb is the area covered by both Pa and Pb, Pa ∉ Pb is the area
of Pa not contained within Pb, and Pb ∉ Pa is the area of Pb not contained
within Pa.
Here, the Dice coefficient is used as a spatial overlap index to test for
site fidelity. Zidjenbos et al. (1994) derive the Dice similarity coefficient
Cohen’s kappa coefficient of agreement, and Landis and Koch (1977)
proposed that kappa coefficient values in the range 0.41–0.60 represent
moderate similarity, those between 0.61–0.80 represent substantial similarity,
and those greater than 0.81 represent almost perfect similarity. Values
less than 0.4 represent essentially no similarity. As a result, this study
considered values greater than 0.4 to be evidence of site fidelity. The
intersection of the seasonal polygons for different years was a test for interyear
site fidelity, while the intersection of seasonal polygons within a year
was a test for intra-year site fidelity. To provide additional context on the
degree of home-range shift on an inter- and intra-annual basis, the distance
between home-range centroids (mean x- and y-locations) both within and
between years was also calculated.
Home-range estimation. The Animal Movement extension for ArcView
(Hooge and Eichenlaub 1999) was used for all home-range calculations.
Fixed-kernel estimates used least-squares cross validation (Seaman and
Spd =
576 Northeastern Naturalist Vol. 14, No. 4
Powell 1996). The fi nal reported seasonal home-range sizes use data pooled
for the entire three-year study period. Home ranges were calculated for 23
animals in summer (mean of 28 locations [range = 20–44]), and 22 animals
in winter (mean of 27 locations [range = 21–43]), using both the 100% MCP
and the 95%-isopleth of the fi xed-kernel estimator.
Movement rates and group sizes. Movement rates were calculated as
the mean daily distance traveled between successive relocations, considering
only locations from 12 to 18 days apart, and were assigned to the
month in which the mean date between successive locations fell. Each
time a radio-collared caribou was sighted during a telemetry flight, the
number of animals associated with it was recorded. In a small number
of cases when other groups of caribou were incidentally sighted, their
numbers were also recorded. Although not formally assessed, there did
not appear to be any obvious evidence that the size or composition of
these groups differed. These data were used to describe the distribution
of group sizes observed by month.
Results
Third-order habitat selection. Habitat use was not random at the thirdorder
scale in both summer and winter, and in each of the three study years
(Λ = 0.012 to 0.055, 11 df, p < 0.01). However, habitat rankings were not
signifi cantly different from year to year (Wilcoxon signed rank test: Zw =
0.00 to -0.48, n = 5 to 10, p > 0.63). As a result habitat-use data were pooled
to look for habitat-selection patterns at all scales.
The pooled data also indicated that habitat use differed significantly
from random in both summer and winter (Λ = 0.043 and 0.048, respectively,
11 df, p < 0.01; Table 2). The highest-ranking habitats in summer
were: treed muskeg, water, upland conifer-pine, and upland coniferspruce.
The highest ranking habitats in winter were: upland conifer-pine,
treed muskeg, and upland conifer-spruce. Hardwood habitats were the
lowest-ranking subset of habitats in both seasons. Upland conifer-spruce
and upland conifer-pine habitats were preferred over immature conifer
habitats in a pair-wise comparison in winter, but were not preferred during
summer (Table 2).
Second-order habitat selection. At the second-order scale, habitat use
again differed signifi cantly from random in both summer and winter (Λ =
0.082 and 0.044, respectively, 11 df, p < 0.01; Table 3). The highest-ranking
habitats in summer were: water, treed muskeg, and upland conifer-spruce.
The highest-ranking habitats in winter were: upland conifer-spruce, upland
conifer-pine, treed muskeg, and open wetland. The lowest-ranking habitats
in both seasons were all hardwood habitat types. Again, in a pair-wise
comparison, upland conifer-spruce and upland conifer-pine habitats were
signifi cantly preferred over immature conifer habitat in winter, but were not
preferred in summer (Table 3).
2007 J.M. Metsaranta and F.F. Mallory 577
Site fi delity. The distribution of Dice coeffi cient values for each probability
isopleth for intra-year fi delity in 1999 and 2000 are plotted in Figure 2.
One animal had a Dice coeffi cient value less than 0.4 at the 95% isopleth
in both years. All other animals had Dice coeffi cient values less than 0.4 at
all of the other fi xed-kernel isopleths. The distribution of Dice coeffi cient
values for each probability isopleth for inter-year fi delity to summer and
winter ranges are plotted in Figure 3. Most animals (81%) had Dice coeffi
cient values greater than 0.4 between 1999 and 2000 at the 95% isopleth.
At the 75%, 50%, and 25% isopleths, the number of animals that have Dice
coeffi cient values greater than 0.4 decreases with each successive isopleth.
In summer, 33% of animals have values greater than 0.4 for the 25% isopleth,
and 14% of animals do so in winter. The mean distance between winter
and summer home-range centroids in 1999 was 22.3 km (range = 5.9 to 46.5
km, SD = 12.5 km); in 2000 it was 22.1 km (range = 3.4 to 54.7 km, SD =
13.4 km). The mean distance between winter home-range centroids between
years was 9.5 km (range = 2.5 to 25.4 km, SD = 5.4 km) and in summer it
was 3.3 km (range = 1.0 to 7.6 km, SD = 1.8 km).
Table 2. Compositional analysis matrix of (1) summer and (2) winter third-order habitat selection
(buffered telemetry locations within 100%-MCP home range). Each mean log difference is
replaced by a sign (++ or --) indicating signifi cant differences. Habitat types are ranked in the
order of their importance, with an (H) indicating that they are not signifi cantly different from
the highest-ranked habitat type, and an (L) indicating that they are not signifi cantly different
from the lowest-ranked habitat type. See Table 1 for explanation of habitat-type abbreviations.
(1) Summer TM W UCP UCS OW IC LC OUC NV OUH IH UH Rank
TM ++ ++ ++ ++ ++ ++ ++ ++ 1 (H)
W ++ ++ ++ ++ ++ ++ ++ 2 (H)
UCP ++ ++ ++ ++ ++ ++ 3 (H)
UCS ++ ++ ++ ++ ++ 4 (H)
OW -- ++ ++ ++ ++ 5
IC -- -- ++ ++ ++ 6
LC -- -- -- -- ++ 7
OUC -- -- -- ++ 8
NV -- -- -- -- -- 9 (L)
OUH -- -- -- -- -- -- 10 (L)
IH -- -- -- -- -- -- 11 (L)
UH -- -- -- -- -- -- -- -- 12 (L)
(2) Winter UCP TM UCS LC OW W OUC UH NV IC OUH IH Rank
UCP ++ ++ ++ ++ ++ ++ ++ ++ ++ 1 (H)
TM ++ ++ ++ ++ ++ ++ ++ ++ ++ 2 (H)
UCS ++ ++ ++ ++ ++ ++ ++ 3 (H)
LC -- -- ++ ++ ++ ++ ++ ++ ++ 4
OW -- -- ++ ++ ++ ++ ++ ++ ++ 5
W -- -- -- -- -- ++ ++ ++ ++ ++ 6
OUC -- -- -- -- -- ++ ++ 7
UH -- -- -- -- -- -- ++ ++ 8
NV -- -- -- -- -- -- ++ ++ 9
IC -- -- -- -- -- -- ++ ++ 10
OUH -- -- -- -- -- -- -- -- -- -- 11 (L)
IH -- -- -- -- -- -- -- -- -- -- 12 (L)
578 Northeastern Naturalist Vol. 14, No. 4
Home-range Sizes. Home-range sizes were larger in winter than in
summer using either estimator. Mean home-range size in winter for n = 22
animals was 856 km2 (range = 103 to 2206 km2, SD = 430 km2) using the
100%-MCP estimator and 1386 km2 (range = 126 to 3256 km2, SD = 709
km2) using the 95%-isopleth fi xed-kernel estimator. Mean home-range size
in summer for n = 23 animals was 162 km2 (range = 7 to 975 km2, SD = 201
km2) using the 100%-MCP estimator, and 175 km2 (range = 10 to 670 km2,
SD = 155 km2) using the 95%-isopleth fi xed-kernel estimator.
Movement rates. Movement rates were lowest from May to September,
corresponding to the summer calving and post-calving period (Fig. 4).
Movement rates were highest in April, November, and January. The November
and April peaks corresponded to periods of seasonal range-use shifts,
while the January peak represented a movement from early to late winter-use
areas (Fig. 4).
Table 3. Compositional analysis matrix of (1) summer and (2) winter second-order habitat selection
(50% adaptive-kernel home range within cumulative population range). Each mean log
difference is replaced by a sign (++ or --) indicating signifi cant differences. Habitat types are
ranked in the order of their importance, with an (H) indicating that they are not signifi cantly
different from the highest-ranked habitat type, and an (L) indicating that they are not signifi -
cantly different from the lowest-ranked habitat type. See Table 1 for explanation of habitat type
abbreviations.
W TM UCS OW UCP LC OUC NV IC OUH UH IH Rank
(1) Summer
W ++ ++ ++ ++ ++ ++ ++ ++ 1 (H)
TM ++ ++ ++ ++ ++ ++ 2 (H)
UCS ++ ++ ++ ++ 3 (H)
OW -- ++ ++ ++ ++ 4
UCP ++ ++ ++ 5
LC -- ++ ++ ++ 6
OUC -- -- -- 7 (L)
NV -- -- -- 8 (L)
IC -- -- -- 9 (L)
OUH -- -- -- -- -- -- 10 (L)
UH -- -- -- -- -- -- 11 (L)
IH -- -- -- -- -- -- 12 (L)
(2) Winter
UCS ++ ++ ++ ++ ++ ++ ++ ++ 1 (H)
UCP ++ ++ ++ ++ ++ ++ ++ ++ 2 (H)
TM ++ ++ ++ ++ ++ ++ ++ ++ 3 (H)
OW ++ ++ ++ ++ ++ ++ ++ ++ 4 (H)
W -- -- -- -- ++ ++ ++ ++ ++ 5
LC -- -- -- -- ++ ++ ++ ++ 6
OUC -- -- -- -- ++ ++ ++ 7
NV -- -- -- -- -- ++ ++ 8
UH -- -- -- -- -- -- ++ ++ 9
IC -- -- -- -- -- -- -- ++ 10
IH -- -- -- -- -- -- -- -- -- 11 (L)
OUH -- -- -- -- -- -- -- -- -- -- 12 (L)
2007 J.M. Metsaranta and F.F. Mallory 579
Grouping behavior. Group sizes varied greatly over a year (Fig. 5).
From May to September, group size was limited to two animals, which
usually represented cow-calf pairs. From October to April, the average
group size was 5.1 animals (SD = 3.1, n = 282 sightings). Although not
formally investigated, observations of groups of animals not associated
with radio-collared animals during this period appeared to be of similar
Figure 2. Distribution of Dice coeffi cient values in 1999 and 2000 for intra-year
home-range fi delity of n = 21 woodland caribou in the Naosap area.
580 Northeastern Naturalist Vol. 14, No. 4
size, and have similarly varying sex and age compositions to those that
had radio-collared individuals (Metsaranta 2002). The largest individual
aggregation observed was 20 animals, and groups of more than 10 animals
were regularly sighted.
Figure 3. Distribution of Dice coeffi cient values in winter and summer for inter-year
home-range fi delity of n = 21 woodland caribou in the Naosap area.
2007 J.M. Metsaranta and F.F. Mallory 581
Discussion
Habitat selection. Mature coniferous forests were highly ranked habitat
types in both summer and winter, as in other studies (e.g., Bradshaw et al.
1995, Mahoney and Virgil 2003, Mosnier et al. 2003, Rettie and Messier
2000). However, in a pair-wise comparison, mature coniferous habitats were
not used more than immature conifer forests. Rettie and Messier (2000) also
found that, in certain populations, animals showed a selective inclusion of
immature forest types, speculating that this represented historical habitatselection
patterns, and that where annual shifts occurred, they tended to
show avoidance of immature forest types. This is likely also the case in this
study. Avoidance of immature forest types would tend to show the selective
avoidance of moose and consequently higher predator populations associated
with moose, since moose tend to be more prevalent in young forests.
Winter habitat types selected consisted primarily of a mosaic of mature upland
spruce and pine conifer forests and open or semi-open treed muskegs.
The habitat types selected in winter are common throughout the study area,
together accounting for about 50% of the total available habitat in the study
area. In summer, the strong selective inclusion of water at both spatial scales
is similar to previous studies where caribou have been noted to occur near
water (on islands and peninsulas or near lakeshores) during this period as an
Figure 4. Box and whisper plot of daily distance traveled in each month by woodland
caribou in the Naosap area. The ends of the box represent the lower and upper
quartiles, the whiskers represent the 10th and 90th percentiles, and the dots represent
the 5th and 95th percentiles. The solid line in the box represents the mean, and the
dashed line in the box represents the median.
582 Northeastern Naturalist Vol. 14, No. 4
anti-predator strategy (Bergerud et al. 1990). Unlike recent studies (Ferguson
and Elkie 2005), caribou here did not show any selective use of frozen
lakes during the winter.
Animals in this population did not select mature over immature coniferous
habitats, which could indicate that their habitat quality remains
adequate during the summer, and that specific mitigation plans for forest
harvesting near summer-use areas that maintain buffer areas and access
corridors around lakes where caribou are known to use islands and peninsulas
to calve appear to be allowing adult female caribou to continue using
those areas. It may also indicate that moose populations may not have had
enough time to increase after disturbance, and thus, predation pressure on
caribou had not yet increased. Moose would tend to be found in higher
numbers in hardwood forest types, which were ranked the lowest at all spatial
and temporal scales. This suggests that should silvicultural practices
successfully regenerate coniferous forests, this would help ensure future
availability of woodland caribou habitat, and possibly maintain present
populations. If silvicultural practices do not successfully regenerate coniferous
habitats (e.g., Carleton and MacClennan 1994), if management
Figure 5. Box and whisper plot of group sizes in each month by woodland caribou
in the Naosap area. The ends of the box represent the lower and upper quartiles, the
whiskers represent the 10th and 90th percentiles, and the dots represent the 5th and 95th
percentiles. The solid line in the box represents the mean, and the dashed line in the
box represents the median.
2007 J.M. Metsaranta and F.F. Mallory 583
practices favor increased forage for other ungulates (e.g., Strong and
Gates 2006), or if post-logging successional pathways differentially favor
other ungulates over caribou (e.g., Metsaranta, in press), then this situation
would be a concern for maintaining caribou populations.
Home-range sizes. As in many other studies (e.g., Edmonds 1988, Mahoney
and Virgil 2003, Rettie and Messier 2001, Stuart-Smith et al. 1997),
home-range sizes were larger in winter than in summer. In studies with the
most-similar seasonal defi nitions (Edmonds 1988, Stuart-Smith et al 1997),
the reported home-range sizes ranged from 147 to 650 km2 in winter and 24
to 536 km2 in summer. These are smaller than the 856-km2 winter-range size,
but similar to the 162-km2 summer-home size, observed here.
Intra-year site fidelity. Caribou in this region used distinct areas in
summer and winter. This is consistent with some studies (e.g., Bergerud
et al. 1990, Cumming and Beange 1987, Shoesmith and Storey 1977),
but not others (e.g., Ouellet et al 1996, Stuart-Smith et al. 1997). In cases
where animals calve and spend the summer on islands and peninsulas
of large lakes typical of the boreal shield ecozone, wintering areas are
often separate and distinct mainland areas (Bergerud et al. 1990, Cumming
and Beange 1987, Shoesmith and Storey 1977). In cases where
animals occupy large peatland areas, typical of the boreal plains ecozone,
distinct winter and summer areas are absent (Stuart-Smith et al. 1997).
The animal in this study that used overlapping seasonal ranges was in the
southern portion of the study area, where large continuous peatlands typical
of the boreal plains are common. The rest of the animals in this study
occupied distinct areas during summer and winter, and were in the northern
portion of the study area, where numerous lakes and islands typical of
the boreal shield are common.
Inter-year site fidelity. Animals broadly use the same seasonal areas
year after year (95% and 75% isopleths). Other studies have also documented
strong tendencies to site fidelity in this species (Rettie and Messier
2001, Schaeffer et al. 2000, Wittmer et al. 2006). However, animals in the
present study exhibited slight shifts in the core areas (50% and 25%
isopleths) used in winter. Caribou broadly used the same areas in winter
(similarity of 95% and 75% isopleth between years), but did not necessarily
return to precisely the same locations (less similarity in the 50% and
25% isopleths between years). Cumming and Beange (1987) and Wittmer
et al. (2006) made similar observations of small changes in wintering areas
from year to year, even though the areas were broadly similar from year to
year. Cumming (1996) speculated that winter-use areas are implicit refuges
from predation, while Wittmer et al. (2006) speculated that changes
in winter-use areas occur in response to forage availability. In either case,
if alternate habitats are available, then disruption of winter habitats may
not be detrimental, as long as forests regenerate to suitable conditions and
caribou are able to disperse to alternate areas. It is not known if alternate
584 Northeastern Naturalist Vol. 14, No. 4
wintering areas are present on this range, and they may not be detectable if
animals themselves do not disperse there (Cumming 1996).
Movement rates. Individuals traveled an average of 0.3 km day-1 in
summer, and an average of 0.8 km day-1 in winter. These can only be considered
rough estimates of movement rates since the straight-line distance
between two locations taken two weeks apart may not be strongly correlated
with the actual distances moved. Regardless, they are consistent
with observations elsewhere (e.g., Benoit 1996, Fuller and Keith 1981,
Stuart-Smith et al. 1997). Peak rates occurred in April, November, and
January. The April peak is consistent with previous observations in the
region made in the late 1970s (Benoit 1996). However, these previous
observations also show two smaller peaks of movement in October and
late December (Benoit 1996), not in November and January. This could
be a change in the timing of seasonal migrations in response to changing
snow-depth patterns (e.g., Darby and Pruitt 1984, Stardom 1975). As
these peaks occur earlier now than they did 25 years ago, this indicates
that snow accumulation have recently occurred later in the year than in
the past. Weather records at The Pas airport support this contention. Peak
snow depths have been declining since records began in 1944, and the
winter of 1999–00 had the lowest and 2000–01 had the sixth lowest recorded
peak snow accumulation since that time.
Grouping behavior. From May to September, cow-calf pairs were the
primary group observed. Group size peaked in November at a mean of 6.3
animals. From October to April, the mean group size was 5.1 (SD 3.1),
which is consistent with woodland caribou observed elsewhere (e.g., Brown
et al. 2000, Darby and Pruitt 1984, Rettie and Messier 1998, Stuart-Smith et
al. 1997). In a previous study of this region, Shoesmith and Storey (1977)
noted group sizes ranging from 2 to 14 animals, with a peak average of 6 in
December. Thus, grouping behavior of the present study is concordant with
past observations of this population.
Conclusions
This study found that the population of caribou living in the Naosap range
in west central Manitoba has ecological characteristics that are similar to other
populations of woodland caribou across Canada. Hardwood forest types were
the lowest-ranked habitat types at all scales examined, which is a concern if
silvicultural practices are not successful at regenerating conifer forests. In
the long term, regenerating coniferous forests after logging, which is generally
consistent with regional forest-management objectives, is necessary
to maintain forests in a condition that resembles habitat currently used by
this species in the region. However, this may not be suffi cient (Metsaranta,
in press; Metsaranta et al. 2003) because of differences in post-logging and
post-fi re successional pathways that may, in the case of logging, differentially
2007 J.M. Metsaranta and F.F. Mallory 585
favor other ungulates over caribou. In summer, mature conifer forests are not
preferred over immature conifer forests in a pair-wise comparison. This may
indicate that in the short-term, specifi c mitigation plans for forest harvesting
(Tolko Industries 1999) that maintain buffer areas and access corridors around
lakes where caribou are known to use islands and peninsulas to calve appear
to be allowing adult female caribou to continue using those areas. However,
this may be because not enough time has yet passed to see a signifi cant change
in the populations of other ungulates, particularly moose, and the concurrent
increase in predation pressure on caribou. The most-recent population surveys
estimate that the mean density of moose in the study area ranges from 0.09 to
0.15 individuals km-2, reaching a maximum of 0.40 moose km-2 in some areas
(Cross 1996, 2000). Although wolves are known to be present, there is no
available estimate of their density. This density of moose present may not
be able to support a high density of wolves on its own (Gasaway et al. 1992,
Messier 1994, Messier and Crete 1985). Because of this, the wolf population
is probably jointly supported by both moose and caribou, limiting caribou at
low densities, but permitting a stable population (Rettie and Messier 2000).
Unlike in summer, mature coniferous forests were preferred over immature
coniferous forests during winter. Where caribou choose to be during winter
might represent an implicit refuge from predation (Cumming 1996). The presence
of other such refuges on this range is not known, suggesting that areas
currently used during winter should be protected from disturbance. As a result
of the uncertainty of moose and wolf populations, and the uncertainty as to the
presence of alternate winter areas, the long-term effectiveness of mitigation
plans needs to be monitored.
Acknowledgments
We thank Manitoba Conservation, Tolko Industries, and Manitoba Hydro for
fi nancial support. We also thank Dale Cross for conducting much of the radiotelemetry
work, the pilots at Jackson Air Services for skillful fl ying, and Becky
Farguson for able assistance during two fi eld seasons. We also thank the numerous
other Manitoba Conservation and Tolko Industries staff in The Pas, MB who contributed
to this work over the years. J.M. Metsarana was supported by a Natural Science
and Engineering Resource Council of Canada scholarship, as well as a Laurentian
University Graduate Fellowship while conducting this work. The comments of two
anonymous referees helped to improve the manuscript.
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