Changes in Occupancy and Relative Abundance of a
Southern Population of Spruce Grouse Based on a 25-year
Resurvey
Christopher Gilbert and Erik Blomberg
Northeastern Naturalist, Volume 26, Issue 2 (2019): 275–286
Full-text pdf (Accessible only to subscribers. To subscribe click here.)
Access Journal Content
Open access browsing of table of contents and abstract pages. Full text pdfs available for download for subscribers.
Current Issue: Vol. 30 (3)
Check out NENA's latest Monograph:
Monograph 22
Northeastern Naturalist Vol. 26, No. 1
C. Gilbert and E. Blomberg
2019
275
2019 NORTHEASTERN NATURALIST 26(2):275–286
Changes in Occupancy and Relative Abundance of a
Southern Population of Spruce Grouse Based on a 25-year
Resurvey
Christopher Gilbert1,* and Erik Blomberg1
Abstract - Marginal populations are often distributed throughout fragmented landscapes
and experience less optimum conditions compared to central range populations. Falcipennis
canadensis (Spruce Grouse) inhabit conifer-dominated forests distributed throughout
the northern US and Canada, and reach their southeastern range extent in the northeastern
US, including Maine. We resurveyed 18 forest stands on Mount Desert Island, ME, that
were comprised of Picea mariana (Black Spruce) and Larix laricina (Tamarack) and which
were originally surveyed during 1992–1993. Our goal was to observe changes in Spruce
Grouse occupancy and abundance between the 1990s and the present (2017). We conducted
repeated callback surveys to detect territorial male Spruce Grouse within each stand during
spring 2017, using a systematic survey design that covered the entirety of each stand and
replicated methods used during the 1990s. We documented 7 individual Spruce Grouse,
including 6 males and a single female. Single-season occupancy models for 2017 predicted
Spruce Grouse stand occupancy of 0.226 (±0.100 SE), with a survey-level detection probability
for male Spruce Grouse of 0.857 (±0.141 SE). Stand occupancy decreased from
8 stands in 1992–1993 to 4 in 2017, a 50% decline in the proportion of stands occupied.
Further, the total number of males observed decreased from 32 (average between 1992 and
1993) to only 6 during our study, a >80% decline in apparent abundance. Our results suggest
Spruce Grouse populations on Mount Desert Island have decreased and may be at risk
of local extinction.
Introduction
Species are confined to a geographical range with limits imposed by abiotic and
biotic factors. In most cases, the center of a species’ range contains optimal abiotic
conditions and the greatest availability of continuous suitable habitat (Hargrove
and Rotenberry 2011). Range margins often occur along ecological gradients,
which impose the biotic or abiotic limits that define the boundaries of the species’
range (Sagarin and Gaines 2002). A common feature among species in the center
of their range are often less sensitive to environmental changes compared to those
a the margin because of greater abundance and genetic diversity (Grant and Antonovics
1978). Patches of habitat at range margins are often smaller in area and
interspersed within a non-habitat matrix, causing greater isolation compared to
habitat within the center of a species’ range (Guo et al. 2005). As a result, local
populations become smaller and genetically isolated (Grant and Antonovics 1978),
increasing the probability of localized extinction due to lower abundance, lack of
1Department of Wildlife, Fisheries and Conservation Biology, University of Maine Orono,
ME 04469. *Corresponding author - christopher.gilbert1128@gmail.com.
Manuscript Editor: Peter Paton
Northeastern Naturalist
276
C. Gilbert and E. Blomberg
2019 Vol. 26, No. 1
genetic diversity, or lower connectivity. These factors may in turn reduce a population’s
ability to adapt to environmental or land-use changes (Guo et al. 2005). In
this study, we conducted a re-survey of Falcipennis canadensis L. (Spruce Grouse)
stand occupancy and relative abundance for an isolated island population at the
southern extent of the species’ range.
Spruce Grouse is a northern conifer forest obligate that is often associated with
mid-successional forests, although habitat characteristics vary widely across the
species’ range (Schroeder et al. 2018). Much of Spruce Grouse range is in the boreal
forest, the conifer-dominated forests of high northern latitudes (Aldrich and Duvall
1955, Bent 1932, Williamson et al. 2008). These forests are composed primarily
of Pinus spp. (pines), Picea spp. (spruces), or Larix spp. (larches) (Kaplan 1996).
Spruce Grouse habitat in Maine, at the southeastern extent of the species’ range, is
primarily forested wetlands composed of Picea rubens Sarg. (Red Spruce), Picea
mariana (Mill.) Britton, Sterns & Poggenburg (Black Spruce), Abies balsamea (L.)
Mill. (Balsam Fir), and Larix laricina (Du Roi) K. Koch (Tamarack), with horizontal
cover often comprised of ericaceous shrubs (Dunham 2016, Schroder et al. 2018,
Whitcomb et al. 1996b).
Since the early 1990s, Spruce Grouse populations have declined at the southeastern
extent of their range (Bouta 1991, Ross et al. 2016). The occurrence of
conifer forest patches within a deciduous forest matrix has subdivided Spruce
Grouse populations making them more prone to localized extinction (Ross et al.
2016). Spruce Grouse are known to have annual home ranges of 4 ha; habitat
deemed suitable for Spruce Grouse populations was previously believed to be a
minimum of 20 ha in size (Fritz 1979). Prior research on Mount Desert Island, ME,
found that Spruce Grouse occurred in habitat patches from 8 ha to 26 ha (Whitcomb
et al. 1996b), smaller than the minimum size described by Fritz (1979). Whitcomb
et al. (1994) also suggested that Spruce Grouse on Mount Desert possessed characteristics
of a spatially structured population, occupying highly fragmented conifer
patches isolated within a deciduous forest landscape, which could increase risk of
localized extinction.
Whitcomb et al. (1996b) surveyed all stands on Mount Desert Island dominated
by Black Spruce and Tamarack, which they presumed to reflect the majority
of available Spruce Grouse habitat on the island. Our research objectives were
to (1) resurvey these stands 25 y later to determine changes in Spruce Grouse
occupancy and relative abundance, and (2) investigate the relationship between
Spruce Grouse occupancy and stand size. We hypothesized that Spruce Grouse
occupancy and abundance have declined since the Whitcomb et al. (1996b) study
based on research from other populations in the northeastern US at the southern
extent of the species’ range (Ross et al. 2016). We also predicted that larger
stands would support a greater number of individuals, increasing the likelihood
of persistence, and thus, present occupancy, because risk of local extinction due
to demographic stochasticity decreases with increasing population size (Grant
and Antonovics 1978).
Northeastern Naturalist Vol. 26, No. 1
C. Gilbert and E. Blomberg
2019
277
Field-site Description
We conducted our study on Mount Desert Island (MDI), ME. The island is situated
in the Gulf of Maine, approximately 0.6 km from the mainland and has an
area of 281 km2 (Fig. 1). MDI is an island with moderate to steep topography as a
result of north-to-south ridges and U-shaped valleys (Patterson et al. 1983). The
Figure 1. Map of Mount Desert Island, ME, showing the location, relative size, and occupancy
status of each Black Spruce–Tamarack stand surveyed for Spruce Grouse occupancy
during the spring of 2017. We compared stand occupancy between surveys conducted
during 1992–1993 by Whitcomb et al. (1996b) and our surveys of the same stands during
2017. Symbol size is proportional to stand size, and the dark irregular polygons indicate
major inland water bodies on Mount Desert Island for spatial reference. The inset map in
the upper left provides the approximate current range (dark gray) of Spruce Grouse in the
Northeastern US and the location of Mount Desert Island (white star).
Northeastern Naturalist
278
C. Gilbert and E. Blomberg
2019 Vol. 26, No. 1
landscape on MDI consists of both deciduous and conifer forests with a mix of private
ownership and federally managed lands associated with Acadia National Park.
We conducted our research at 18 forest stands located throughout MDI that were
originally identified and surveyed by Whitcomb et al. (1996b) during 1992 and
1993. These stands occur on poorly drained soils, are dominated by Black Spruce
and Tamarack, and are thought to contain the majority of potential habitat for
Spruce Grouse on MDI (Whitcomb et al. 1996b). Some stands extend onto adjacent
uplands with well-drained shallow acidic soils. Stand structural characteristics were
variable. Mid-story cover consisted of dense clusters of Black Spruce and Tamarack
saplings, and ericaceous shrubs. Patches of Red Spruce and Balsam Fir, as well as
patches of Alnus incana (Nutt.) Breitung (Speckled Alder) and Acer rubrum L. (Red
Maple) were adjacent to many Black Spruce stands. Some sites had intermixed
Thuja occidentalis L. (Northern White Cedar), which also occurs in areas of poorly
drained soils. Some stands near uplands were also bordered by either coniferous
forests containing Red Spruce, P. glauca (Moench) Voss (White Spruce), Balsam
Fir, and P. strobus L. (White Pine) or by deciduous forest dominated by Betula papyrifera
Marshall (White Birch) and Populus tremuloides Michx. (Quaking Aspen).
Nine of the 18 stands are within the boundaries of Acadia National Park, 7 stands
are on private land, and 2 stands are located on both privately-owned and national
park lands.
Methods
Breeding patch surveys
We conducted stand occupancy surveys for breeding male Spruce Grouse during
the spring of 2017, beginning on 15 April and continuing until 25 May, generally
following the same methods used by Whitcomb et al. (1996b). We spaced survey
points 150 m apart, following a grid system, such that we surveyed the entire footprint
of each stand. To create the gird system, we employed ArcGIS to overlay a
150 m x150 m grid over each of the 18 plots that were designated by Whitcomb et
al (1996b). We extracted a UTM coordinate from the center of each grid cell and
converted these into latitude–longitude coordinates on a GPS device (GPS-72H;
Garmin, Olathe, KS). We began surveys 30 min prior to sunrise and ended them
before 1:00 pm. We used a FOXPRO Game Caller (Model NX4; FOXPRO Inc.,
Lewiston, PA) to play recordings of a female Spruce Grouse aggression or “cantus”
call, followed by a recording of a male flutter-flight display. After each sequence of
female and male calls, we listened for 1 min for a reciprocal flutter-flight or watched
for approaching grouse. We repeated this process twice before moving to the next
survey point, and recorded the number of male and female Spruce Grouse observed
at each survey point. These survey methods are commonly used for Spruce Grouse
studies (Bouta 1991, Dunham 2016, Ross et al. 2016, Whitcomb et al. 1996b). Male
Spruce Grouse hold and defend individual territories throughout the breeding season
(Schroeder et al. 2018); thus, we assumed that males observed repeatedly at the
same location represented the same individual. We also assumed that when we detected
males at >1 survey point within a stand, they were unique individuals, due to
Northeastern Naturalist Vol. 26, No. 1
C. Gilbert and E. Blomberg
2019
279
the territoriality and high site-fidelity of males during the breeding season (Schroeder
et al. 2018). In practice, our detections of males were relatively infrequent and
not located at immediately adjacent survey points, so we feel this assumption is
robust. In addition to survey data, we recorded survey start time and temperature,
as well as wind speed using a digital anemometer (Hold Peak, HP-866B). We conducted
all research within Acadia National Park under National Park Service permit
number ACAD-2017-SCI-0018.
Data analysis
We used single-season stand-occupancy models to evaluate differences in the
probability of Spruce Grouse occupancy among stands and also the probability of
detection during a single survey (Mackenzie et al. 2002). In order to run the occupancy
model, we aggregated point-level survey data into a stand-level history
that included the 2 replicated surveys of each stand (see Supplemental Appendix 1,
available online at http://www.eaglehill.us/NENAonline/suppl-files/n26-2-N1687-
Gilbert-s1, and for BioOne subscribers, at https://dx.doi.org/10.1656/N1687.s1).
We believe our sampling protocol meets the general assumptions of the singleseason
occupancy model (Mackenzie et al. 2002) for closure among repeated surveys
and independence among sample stands, particularly because we conducted
all surveys within a single Spruce Grouse breeding season, and individual forest
stands were spatially distinct and separated by distances that far exceeded male
Spruce Grouse territory size. These models also assume homogenous occupancy
probability among sites, and detection probabilities among sites and surveys, and
we accommodated potential heterogeneity in occupancy and detection by incorporating
a number of site- and survey-level covariates (described below).
We tested multiple variables that we hypothesized could affect either occupancy
or detection probability. These parameters included wind speed, ordinal day, and
start time relative to sunrise as survey-level detection variables, and stand size as
a site-level occupancy variable. The ambient noise produced by wind may affect
an observer’s ability to hear flutter flights and territorial calls (Conway and Gibbs
2001). Prior Spruce Grouse research has shown that males tend to respond more to
callbacks during peak breeding season but are less likely to respond to such stimuli
later in the season (Robinson 1980). It has been found that Spruce Grouse males
tend to be more active during the early morning hours, and their call and display
frequency decreases as time approaches noon (Schroeder et al. 2018). Spruce
Grouse are commonly found in patches greater than 20 ha (Fritz 1979, Ross et al.
2016), but previous studies on MDI found that Spruce Grouse were also found in
patches smaller than 20 ha (Whitcomb et al. 1996b).
We conducted a single-season occupancy analysis (Mackenzie et al. 2002) using
the ‘unmarked’ package in program R (R Core Team 2013). We initially attempted
to fit the model under a penalized likelihood (Hutchinson et al. 2015); however,
these models would not converge and so we used the more general single-season
model. We evaluated each detection variable paired with an intercept-only structure
for the occupancy parameter and evaluated the effect of area on occupancy with an
Northeastern Naturalist
280
C. Gilbert and E. Blomberg
2019 Vol. 26, No. 1
intercept-only model for detection probability. We contrasted all of these models’
structures against a null model (intercept only on both occupancy and detection).
We ranked each of the above models using the Akaike information criterion (AIC),
and used ΔAIC to determine the strength of evidence for each model (Burnham and
Anderson 2002), using a criterion of ΔAIC < 2.0. Based on results of initial model
evaluation, we also tested wind as a detection covariate paired with stand size (ha)
as an occupancy covariate, as well as ordinal day as a detection covariate paired
with stand size (ha) as an occupancy covariate. We further evaluated 95% confidence
intervals of the Beta coefficients to see whether they ove rlapped 0.
Following occupancy analysis, we calculated p*, which provides an estimate of
the probability that an animal was detected at least once during n number of repeated
surveys, where p* = 1 – (1 - p)n, and where p is the probability of detecting a Spruce
Grouse during a single survey. Using p* allowed us to evaluate the probability that
we failed to detect Spruce Grouse presence within all truly occupied stands, given
the modeled detection probability from our occupancy analysis and the number of
repeated surveys we conducted. This step was necessary for comparison with the
results of Whitcomb et al. (1996b), who conducted 3 repeated surveys compared to
our 2 surveys.
We did not attempt to model individual abundance within each stand or at each
survey point, such as using the N-mixture approach (Royle 2004). Generally, our
observations of individual Spruce Grouse were infrequent, and we considered our
counts too sparse for this approach. As such, our counts of territorial males represent
relative abundances that are not corrected for imperfect detection, and we
include them largely for comparison with similar values reported by Whitcomb et
al. (1996b). To give context to differences in counts of males between the early
1990s and our study, we approximated individual male detection rates during our
study based on repeated observations at survey points with known territorial males.
We calculated the binomial probability of detection for individual territorial males
that were observed during either 1 or both repeated surveys as p = c / n, where c is
the count of total detections at survey points where a territorial male was observed,
and n is the number of survey points where a male was observed at least once. The
standard error (SE) for the maximum likelihood estimate of p is then given as SE =
(p [1 - p] / n) 0.5. Using this estimate of p, we then calculated p* for individual territorial
male Spruce Grouse, as described above.
Results
We conducted callback surveys twice at 227 survey points spanning 18 stands,
totaling 454 individual callback surveys. We detected Spruce Grouse in 4 of the
18 stands (Fig. 1), and observed 7 unique individuals, including 6 males and 1
female (Table 1). The mean area of stands where we detected Spruce Grouse was
82.2 ha (±107.5 SD), and was 14.0 ha (±18.4 SD) for stands where we did not detect
Spruce Grouse.
Naïve occupancy (proportion of stands where we detected Spruce Grouse) during
our surveys was 0.222. Based on our occupancy models, the average detection
Northeastern Naturalist Vol. 26, No. 1
C. Gilbert and E. Blomberg
2019
281
probability (p) during a single survey was 0.857 (±0.141 SE), and the estimated
occupancy probability (ψ) was 0.226 ± 0.100 SE. Four models were competitive
based on ΔAIC (Table 2) and indicated that wind speed and ordinal day affected
detection probability, while occupancy was affected by stand area. However, confidence
intervals for each of these effects overlapped 0.0, indicating substantial
uncertainty in their support (Table 3). Start time relative to sunrise had no effect
on detection probability (β = 0.00 ± 0.01 SE; Table 4). Based on a detection
probability of 0.857 ± 0.141 SE and each stand being surveyed twice, p* = 0.980,
Table1. Differences in observed Spruce Grouse abundance by sex from surveys on Mount Desert
Island, ME, during the 1992, 1993, and 2017 field seasons. The data from the 1992 and 1993 field
seasons were obtained from Whitcomb et al. (1996b).
1992 1993 2017
Site Males Females Males Females Males Females
Aunt Betsy Brook (ABB) 4 0 3 1 2 0
Aunt Betty Pond (ABP) 4 2 6 4 1 0
Bernard (B) 0 0 0 0 0 0
China Hill (CH) 3 0 2 0 0 0
Dodge Point Road (DPR) 0 0 0 0 0 0
Eagle Lake (EL) 3 1 3 1 0 0
Fresh Meadow (FM) 0 0 0 0 0 0
French Pond (FP) 0 0 0 0 0 0
Hio Bridge (HB) 9 3 5 2 2 1
Jones Marsh (JM) 0 0 0 0 0 0
Pretty Marsh (PM) 3 1 0 0 0 0
Saint Andrews (SA) 0 0 0 0 0 0
Sand Beach (SaB) 0 0 0 0 0 0
Stony Brook (SB) 0 0 0 0 0 0
Southern Heath (SH) 2 1 2 0 1 0
Whalesback (W) 8 6 7 3 0 0
West Mountain East (WME) 0 0 0 0 0 0
West Mountain West (WMW) 0 0 0 0 0 0
Total 36 14 28 11 6 1
Table 2. Model selection statistics for single season occupancy models of Spruce Grouse on Mount
Desert Island, ME, based on repeated male callback surveys conducted during spring 2017. Ψ = probability
of occupancy, p = probability of detection, (.) = y-intercept only, Wind = average wind speed
during a survey, Day = ordinal day of survey, Start = time of survey relative to minutes before sunrise,
and Area = size of stand (ha)
Model K AIC ΔAIC AICwt
pWind,ψArea 4 23.57 0.00 0.3456
pDay,ψArea 4 24.29 0.72 0.2414
pWind,ψ(.) 3 25.07 1.50 0.1633
pDay,ψ(.) 3 25.24 1.66 0.1506
p(.),ψArea 3 27.47 3.90 0.0492
p(.),ψ(.) 2 28.95 5.38 0.0235
pStart,ψ(.) 3 30.83 7.26 0.0092
Northeastern Naturalist
282
C. Gilbert and E. Blomberg
2019 Vol. 26, No. 1
indicating a ~2% chance that we failed to detect Spruce Grouse presence within a
truly occupied stand.
We detected individual males 8 times during 12 point-level surveys where a
male was known to be present based on detection during 1 or more surveys. These
detections yielded an individual detection probability of 0.667 ± 0.137 SE during a
single survey, and an associated estimate of p* = 0.889 for 2 repeated surveys. Thus,
there was an approximately 11% chance that we failed to detect an individual male
Spruce Grouse during our 2 repeated surveys, given that it was present and available
for detection.
Discussion
There was a decrease in stand occupancy as well as apparent abundance of
Spruce Grouse on MDI between our 2017 surveys and those conducted in the early
1990s. During the 1990s, Whitcomb et al. (1996b) documented 36 (1992) and 28
(1993) male Spruce Grouse across 8 occupied stands, while in contrast we only
observed 6 males located in 4 stands. This change reflects a 50% reduction in patch
occupancy and a >80% reduction in apparent abundance of Spruce Grouse compared
with the early 1990s. These results are similar to those observed for Spruce
Grouse in the Adirondack Mountains of New York, where habitat extent declined by
70% and the number of occupied patches declined by 25%, based on resurvey work
conducted over a 40-y period (Ross et al. 2016). Although our study included only
1 y of survey data (discussed below), we nevertheless conducted a comprehensive
survey of all stands surveyed by Whitcomb et al. (1996b). Thus, the change in both
occupancy and apparent abundance we observed reflects a true change during the
25-y interval between the 2 surveys.
Whitcomb et al. (1996b) found that patch size was a primary predictor of Spruce
Grouse presence in the 1990s, where patches >11 ha in size were normally occupied
and smaller patches unoccupied. During our study, all small stands that were
previously unoccupied remained unoccupied; however, some previously occupied
stands, classified as medium and large by Whitcomb et al. (1996b), were now
unoccupied. With only a small number of occupied stands (n = 4), our data likely
lacked power to detect covariate effects on stand occupancy probability. Of the 4
remaining occupied stands, only 1 stand was smaller than 20 ha, however, we also
failed to detect Spruce Grouse in the second largest stand (77 ha). So, while it is
Table 3. Estimates of parameter coefficients (β) from site-occupancy models of male Spruce Grouse
on Mount Desert Island, ME, based on data obtained from callback surveys conducted during April
and May 2017.
95% Confidence interval
Covariate Parameter tested Estimate (β) SE Upper Lower
Stand size (ha) Occupancy 0.02 0.02 0.07 -0.02
Wind speed Detection -6.03 11.60 16.71 -28.77
Ordinal day Detection 1.00 1.01 2.98 -0.98
Start time after sunrise Detection 0.00 0.01 0.02 -0.02
Northeastern Naturalist Vol. 26, No. 1
C. Gilbert and E. Blomberg
2019
283
true that only larger stands remained occupied, apparent loss of Spruce Grouse from
some large stands also suggests that factors other than stand size may be driving
local population dynamics. It is possible that other habitat metrics that we did not
measure affected the decline in occupancy we observed, such as changes in forest
stand characteristics (Dunham 2016) associated with forest succession during the
past 25 y (e.g., Ross et al. 2016), anthropogenic developments occurring outside of
Acadia National Park, or climate change. The patterns could also be due to demographic
stochasticity coupled with low connectivity among stands. Each previously
occupied stand that was unoccupied during our study fell within Spruce Grouse
dispersal distance (Whitcomb et al. 1996a) from an occupied stand, but it is possible
that recruitment rates within the system are insufficient to maintain local patches
through immigration/emigration dynamics.
Although we attempted to replicate Whitcomb et al.’s (1996b) methods as
closely as possible, there were some small differences that we acknowledge may affect
our comparison with their results. We conducted 2 rounds of callback surveys,
while Whitcomb et al. (1996b) conducted 3 rounds, and we also ran an occupancy
analysis accounting for detection probability, while Whitcomb et al. (1996b) used
a naïve occupancy rate without a formal occupancy analysis. Our p* value of 0.980
implies that if we were to conduct a 3rd survey, Spruce Grouse stand occupancy
would remain at 4 out of 18 stands. If detection probability was similar during the
study of Whitcomb et al. (1996b), they too would have observed all occupied stands
(8) during 3 repeated surveys. However, if detection probability was lower during
their study, then differences in stand occupancy probability between 1992–1993
and 2017 would be greater than we have shown. Our survey design had a ~11%
chance of failing to detect an individual territorial male during 2 repeated surveys,
given that it was available for detection. It is therefore possible that we undercounted
the total number of males present by a few birds due to imperfect detection.
Overall, our results show that potential differences in detection probability, both for
occupied stands and individual males, are relatively small when compared with the
large differences in occupancy and apparent abundance between our surveys versus
those of Whitcomb et al. (1996b).
During our surveys, we only detected a single female Spruce Grouse, while
Whitcomb et al. (1996b) observed substantially more females in the same stands.
Our callback surveys were designed to elicit responses from male Spruce Grouse
specifically, and so our sampling methods were not tailored to detecting females.
Differences in the ratio of male to female Spruce Grouse observed between the
2 surveys may reflect true decline in female abundance, which could in turn provide
a demographic mechanism for the overall population declines we observed.
However, given that we did not survey female Spruce Grouse explicitly, we cannot
account for detection probability of females during our surveys, and therefore our
reported count of females should be interpreted cautiously.
Based on our research, Spruce Grouse that inhabit Black Spruce–Tamarack
forests on MDI have declined substantially since the 1990s, and may be at risk of
local extirpation. We conducted our surveys only in lowland Black Spruce–Tamarack
forests; these forest types are generally considered to be the primary habitat
Northeastern Naturalist
284
C. Gilbert and E. Blomberg
2019 Vol. 26, No. 1
of Spruce Grouse in the region (Ross et al. 2016, Whitcomb et al. 1996b). Spruce
Grouse are conifer-forest obligates and do not regularly occur in forests that are not
dominated by conifers (Schroeder et al. 2018). On MDI, it is possible that the species
also occupies upland conifer forests dominated by Red Spruce, White Spruce,
and Balsam Fir (hereafter, upland spruce–fir), which we did not survey for this
study. In the early 1990s, Whitcomb et al. (1994) found that Spruce Grouse rarely
occurred in these upland spruce–fir forests, and only when adjacent to occupied
lowland Black Spruce–Tamarack forests. Future monitoring of Spruce Grouse on
MDI should explore present-day occupancy of upland spruce–fir st ands.
The degree to which MDI Spruce Grouse are isolated (both demographically and
genetically) from mainland populations is also unknown. Mainland Spruce Grouse
are found on the Schoodic Peninsula within ~15 km of the nearest occupied stand on
MDI. Whitcomb et al. (1996a) observed a maximum dispersal distance of juvenile
Spruce Grouse on MDI of 7.2 km (Whitcomb et al. 1996a), while other research has
found individuals able to travel up to 11 km (Schroeder 1985). However, Spruce
Grouse are not known to cross large water bodies, and dispersal to or from the mainland
would require their crossing of Frenchman Bay with an overwater distance >6
km. Geographic isolation, coupled with increased risk of stochastic events due to
low population size (Diamond 1984), suggest that Spruce Grouse on MDI may be at
heightened risk of extirpation. It is possible that we surveyed the population during
a period of short-term population decline, and longer-term monitoring may reveal
a less dramatic pattern. Thus, we recommend further monitoring of this population
to confirm long-term declines and assess the future viability of the population. A
dynamic occupancy modelling approach (MacKenzie et al. 2003) may be useful for
systematic long-term monitoring. If maintenance of Spruce Grouse populations at
their southern range margins is a conservation priority, additional research is likely
needed to identify the causal factors associated with population declines in this and
other systems.
Acknowledgments
We thank Acadia National Park, B. Connery, and K. Anderson for granting access to our
study sites and for field housing. We are grateful to S. Whitcomb and F. Servello for their
input on the project. We thank the University of Maine Honors College and Downeast Audubon
Chapter for financial support. We appreciate A. Mortelliti, A. Calhoun, D. Levesque,
and M. Ladenheim, as well as 2 anonymous reviewers, for helpful comments on earlier
versions of this work. This project was supported by the USDA National Institute of Food
and Agriculture, McIntire-Stennis project #ME041602 through the Maine Agricultural and
Forest Experiment Station. This is Maine Agricultural and Forest Experiment Station Publication
no. 3637.
Literature Cited
Aldrich, J.W., and A.J. Duvall. 1955. Distribution of American gallinaceous game birds.
US Department of the Interior, Fish and Wildlife Service Circular No. 34. Washington,
DC. 23 pp.
Northeastern Naturalist Vol. 26, No. 1
C. Gilbert and E. Blomberg
2019
285
Bent, A.A. 1932. Life histories of North American gallinaceous birds. US National Museum
Bulletin No. 162. Washington, DC. 490 pp.
Bouta, R.P. 1991. Population status, historical decline, and habitat relationships of Spruce
Grouse in the Adirondacks of New York. M.Sc. Thesis. State University of New York
College of Environmental Science, and Forestry, Syracuse, NY. 117 pp.
Burnham, K.P., and D.R. Anderson. 2002. Model Selection and Theoretic Approach. 2nd
Edition, Springer-Verlag, New York, NY.
Conway, C.J., and J.P. Gibbs. 2011. Summary of intrinsic and extrinsic factors affecting
detection probability of marsh birds. Wetlands 31:403–411.
Diamond, J.M. 1984. “Normal” extinctions of isolated populations. Pp. 191–246, In M.H.
Nitecki (Ed.). Extinctions. University. of Chicago Press, Chicago, IL. 354 pp.
Dunham, S.W. 2016. Spruce Grouse habitat ecology in Maine’s commercially managed
Acadian forest. M.Sc. Thesis. University of Maine, Orono, ME. 87 pp.
Fritz, R.S. 1979. Consequences of insular population structure: Distribution and extinction
of Spruce Grouse populations. Oecologia 42:57–65.
Grant, M.C., and J. Antonovics. 1978. Biology of ecologically marginal populations of
Anthoxanthum odoratum. I. Phenetics and dynamics. Evolution 32:822–838.
Guo, Q., M. Taper, M. Schoenberger, and J. Brandle. 2005. Spatial–temporal population
dynamics across species range: From center to margin. Oikos 108:47–57.
Hargrove, L., and J.T, Rotenberry. 2011. Spatial structure and dynamics of breeding bird
populations at a distribution margin, southern California. Journal of Biogeography
38:1708–1716.
Hutchinson, R.A., J.J. Valente, S.C. Emerson, M.G. Betts, and T.G. Dietterich. 2015. Penalized
likelihood methods improve parameter estimates in occupancy models. Methods in
Ecology and Evolution 6:949–959.
Kaplan, E. 1996. The Taiga (Biomes of the World). Benchmark Books, New York, NY.
64 pp.
MacKenzie, D.I., J.D. Nichols, G.B. Lachman, S. Droege, J.A. Royle, and C.A. Langtimm.
2002. Estimating site occupancy rates when detection probabilities are less than one.
Ecology 83:2248–2255.
MacKenzie, D.I., J.D. Nichols, J.E. Hines, M.G. Knutson, and A.B. Franklin. 2003. Estimating
site occupancy, colonization, and local extinction when a species is detected
imperfectly. Ecology 2200–2207.
Patterson, W.A., III., K.E. Saunders, and L.J. Horton. 1983. Fire regimes of coastal Maine
forests of Acadia National Park. Scientific Study No. OSS-83-3. US National Park Service,
North Atlantic Regional Office, Boston, MA.
R Core Team. 2013. R: A language and environment for statistical computing. R Foundation
for Statistical Computing, Vienna, Austria.Available online at http://www.R-project.org/.
Robinson, W.L. 1980. Fool Hen: The Spruce Grouse on the Yellow Dog Plains. University
of Wisconsin Press, Madison, WI. 221 pp.
Ross, A.M., G. Johnson, and J.P. Gibbs. 2016. Spruce Grouse decline in maturing lowland
boreal forests of New York. Forest Ecology and Management 359:118–125.
Royle, J.A. 2004. N-mixture models for estimating population size from spatially replicated
counts. Biometrics 60:108–115.
Sagarin, R.D., and S.D. Gaines. 2002. The “abundant centre” distribution: To what extent
is it a biogeographical rule? Ecology Letters 5:137–147.
Schroeder, M.A., E.J. Blomberg, D.A. Boag, P. Pyle, and M.A. Patten. 2018. Spruce Grouse
(Falcipennis canadensis). In P.G. Rodewald (Ed.). The Birds of North America. Cornell
Lab of Ornithology, Ithaca, NY. Available online at https://doi.org/10.2173/bna.
sprgro.02. Accessed 11 February 2018.
Northeastern Naturalist
286
C. Gilbert and E. Blomberg
2019 Vol. 26, No. 1
Whitcomb, S.D., F.A. Servello, and A.F. O’Connell Jr. 1994. Population and habitat assessment
for Spruce Grouse in Acadia National Park and on Mount Desert Island,
Maine. National Park Service Technical Report NPS/NAROSS/NRTR-94/23. Boston,
MA. 54 pp.
Whitcomb, S.D., A.F. O’Connell Jr., and F.A. Servello. 1996a. Productivity of the Spruce
Grouse at the southeastern limit of its range. Journal of Field Ornithology 67:422–427.
Whitcomb, S.D., F.A. Servello, and A.F. O’Connell Jr. 1996b. Patch occupancy and dispersal
of Spruce Grouse on the edge of its range in Maine. Canada Journal of Zoology
74:1951–955.
Williamson, S.J., D.M. Keppie, R. Davison, D. Budeau, S. Carriere, D. Rabe, and M.A.
Schroeder. 2008. Spruce Grouse continental conservation plan. Association of Fish and
Wildlife Agencies, Resident Game Bird Working Group, Washington, DC. 60 pp.