J Ornithol (2008) 149:245–252
DOI 10.1007/s10336-007-0267-5
ORIGINAL ARTICLE
Habitat partitioning in endangered Cantabrian capercaillie
Tetrao urogallus cantabricus
Marı́a-José Bañuelos Æ Mario Quevedo Æ
José-Ramón Obeso
Received: 12 June 2007 / Revised: 6 September 2007 / Accepted: 6 December 2007 / Published online: 9 January 2008
Ó Dt. Ornithologen-Gesellschaft e.V. 2007
Abstract The endangered Cantabrian capercaillie (Tetrao
urogallus cantabricus) lives at the southern edge of
tetraonids’ distribution range, in entirely deciduous forests.
Its conservation planning has been always lek-centred.
There is very little information about the specific habitat
requirements of hens and broods, even though reproductive
success appears to be a limiting factor. We analysed summer
surveys from 1997 to 2004, carried out to estimate the
reproductive success of the population. We compared the
habitat characteristics at different spatial scales of hens with
broods, broodless hens, and cocks in summer, with the better
known spring habitat in display areas. Summer habitat
showed higher proportion of open areas and was associated
with more rugged zones at moderate spatial scales (78 ha)
than spring habitat at display areas. Cocks and hens showed
summer habitat partitioning; hens were associated with
higher proportions of open and shrubby habitats. Furthermore, broodless hens preferred areas with higher slope
variability than the display and summer areas preferred by
cocks. These differences may reflect the sexual dimorphism
of the species in reproductive role, energetic demands and
conspicuousness. At larger spatial scales a previously
developed habitat suitability model performed well to predict good brood-rearing areas. Hens with broods were
located in the best-preserved areas in the range, mainly
characterized by higher proportion of forest cover at a large
(50 km2) scale. We suggest that these characteristics
Communicated by F. Bairlein.
M.-J. Bañuelos M. Quevedo (&) J.-R. Obeso
Ecology Unit, Department of Biology of Organisms
and Systems, Oviedo University, Campus del Cristo,
33006 Oviedo, Spain
e-mail: quevedomario@uniovi.es
indicate refuge habitats where Cantabrian capercaillie can
still breed successfully.
Keywords Cantabrian capercaillie Brooding hens
Habitat partitioning Habitat suitability
Edge populations Deciduous forests
Introduction
Intraspecific differences in habitat use by animals are often
caused by sex-specific selection pressures and competitive
exclusion (e.g., Selander 1966; Bleich et al. 1997; Ardia and
Bildstein 2001). Even within sexes, the reproductive status
may impose differences in habitat use due to differential
resource acquisition, shelter requirements or role in reproduction. Such variability should be taken into account to
develop sound conservation measures; otherwise actions
could neglect or even harm parts of a population, thus
hampering the conservation of the whole (Durell 2000;
Bolnick et al. 2003). Habitat partitioning is often evaluated
in relation to small-scale habitat features (such as the
importance of understorey cover or insect availability for
grouse species). However, the understanding of large-scale
spatial patterns of suitable habitats and how populations
partition their use provides valuable information for the
development of management strategies (Collinge 2001).
This study is about Cantabrian capercaillie (Tetrao
urogallus cantabricus), a subspecies listed as endangered
according to IUCN criteria (Storch et al. 2006). Cantabrian
capercaillie occupies a very southerly range within the grouse
family (Quevedo et al. 2006b), and has recently been identified
as an Evolutionarily Significant Unit because of its unique
ecological and genetic characteristics (Rodrı́guez-Muñoz et al.
2007). The population appears to show low recruitment, with
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J Ornithol (2008) 149:245–252
values as low as 0.54 juveniles per hen at the end of the summer
and 74% of broodless hens in an 8-year period (Bañuelos et al.
this study, see ‘‘Methods’’ for details). However, there is no
information available about the habitat requirements of hens
with broods, and this is compromising the design and
enforcement of protected areas (Quevedo et al. 2006a, b).
Diverse habitat characteristics are important for brooding hens
in other populations: presence of moist areas (Wegge et al.
2005), presence of anthills (Storch 1993), diverse vegetation
structure (Klaus et al. 1986), treeline meadows (Menoni 1990)
or forest gaps (Saniga 1996). There is, however, a unifying
feature: a relatively high cover of ericaceous shrubs, particularly Vaccinium myrtillus. This has been attributed to the high
abundance of invertebrates in these habitats, which constitute
the main diet of chicks during the first weeks, and to the refuge
against predators provided by these plants (Jacob 1987;
Atlegrim and Sjöberg 1995; Picozzi et al. 1999).
Grouse are, overall, a sexually dimorphic family, and habitat partitioning exists throughout the seasonal cycle (Bergerud
and Gratson 1988). However, most information about habitat
use in capercaillie is biased towards cocks and often corresponds to their conspicuous behaviour at display areas and their
surroundings in spring (e.g., Rolstad and Wegge 1987; Picozzi
et al. 1992). The Cantabrian capercaillie is no exception to this
(Quevedo et al. 2006b). A habitat suitability map, aimed as a
conservation tool, was developed for this population from data
corresponding to occupied and abandoned leks (Quevedo et al.
2006a). However, the validity of this map to predict suitable
habitat for hens with broods remained to be tested. The aim of
our study was to analyse habitat use by Cantabrian capercaillie
during the brood rearing season for a broad range of spatial
scales, helping to fill the gaps in the understanding of this
population. Although small-scale features are, indeed, related
to many aspects of habitat selection, we focused on the landscape scale often required by managers.
The specific aims were as follows:
1.
2.
3.
To determine whether habitat partitioning exists in
relation to sex and reproductive status.
To assess how much the summer habitat differs from
the much better known spring habitat of cocks
attending leks.
To evaluate the performance of a lek-based habitat
suitability map as a decision-support tool to identify
brood-rearing habitats.
Methods
Capercaillie dataset and study area
This study was carried out in the northern watershed of the
Cantabrian Range (Asturias, NW Spain, Fig. 1), where the
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Fig. 1 Area of occupancy of Cantabrian capercaillie (grey areas)
according to the last complete census in 2000, and study sites (black
zones). The grey line shows the approximate division between the
northern and southern watersheds of the Cantabrian Range
Cantabrian capercaillie inhabits a rugged montane landscape of beech (Fagus sylvatica), sessile oak (Quercus
petraea) and birch (Betula pubescens) forests. A detailed
description of the area and habitat characteristics can be
found elsewhere (Quevedo et al. 2006a, b). The study is
based on eight summer surveys (1997–2004) of capercaillie
reproductive success, carried out by the Asturian Environmental Agency. These surveys consisted of drives with
trained dogs, conducted between late July and early September. Note that in the Cantabrian Mountains, as in the
Pyrenees and the Alps (Menoni 1990; Martı́nez 1993;
Storch 1994), capercaillie reproduction appears to occur
3–4 weeks later than in northern populations (Moss et al.
2001; Wegge et al. 2005). More precisely, the information
available from observation of nests and of the size of
juveniles in the summer surveys suggests that hatching
takes place in June and early July.
Forests in the northern watershed of the Cantabrian
Range are highly fragmented (about 22% of the montane
area above 700 m), dominated by beech and oak (Quevedo
et al. 2006b). Beech forests are more frequent in the central
and eastern parts of the range, whereas oak dominates in
the western areas. Birch patches are widespread, often
forming the tree line of those oak and beech forests (Dı́azGonzález and Vázquez 2004). Thus, forest patches frame a
patchy landscape of habitat matrix. In this context, the
surveys were typically performed over continuous areas
that included a diverse mosaic of beech and oak forest,
treeline birch, brooms (Citysus spp., Genista spp.), heaths
(Erica spp., Calluna vulgaris) and open areas (mostly
pastures and scree).
We compiled a list of all the sightings of hens with
broods, broodless hens and cocks collected during those
summer surveys, which totalled 100 field-days and were
carried out in 31 different areas where rangers had previously reported the presence of capercaillie. The surveyed
areas are among the best capercaillie spots in the Cantabrian Mountains (Fig. 1). Nevertheless, even in these areas,
J Ornithol (2008) 149:245–252
densities are low and the terrain is rough, often yielding
only one hen (or none) per field-day. The area covered in
one field-day was, on average, 64 ha (range 15–165 ha),
and the average area surveyed per year was 8.5 km2. The
location of each sighting was recorded with a global
positioning system (GPS) device, and the information on
flushed capercaillies was noted, including sex, age (juvenile or adult) and number of juveniles with the hen. We
selected observations where sex could be determined
(n = 173) and added 15 additional chance observations
registered in the same years by other researchers, forest
rangers and ourselves for a total of 188 summer sightings.
Observations tagged in the field as potentially belonging to
the same bird were discarded from the analyses. So that the
habitat in those summer locations could be compared with
cock spring habitat, the database was completed with the
locations corresponding to all known display grounds
occupied at least at some point during the past 10 years and
located closer than 2 km from the summer observation
sites (N = 100). See Quevedo et al. (2006b) for details on
the characteristics of display grounds in the Cantabrian
Mountains.
Habitat dataset
Information on habitat variables was extracted from a highresolution geographic information system (GIS) database
(Quevedo et al. 2006a, b). The information on land cover
was summarized into four major habitat types to check for
habitat partitioning: (1) beech and oak forest, (2) birch
forest, (3) woody shrubs, and (4) meadows and open areas
(Table 1). Note that this scheme does not in any way imply
forest monospecificity, only dominance. The stands thus
classified in our study also included varying amounts of
several other species, such as hazelnut (Corylus avellana),
holly (Ilex aquifolium) and mountain ash (Sorbus aucuparia), to name a few of the most common.
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To characterize the habitat on local scales we defined
circular plots of 50 m, 100 m, 200 m, 300 m, 400 m and
500 m radius around each capercaillie observed, which
roughly corresponded to 1–78 ha, i.e., within the size
range of forest patches occupied by Cantabrian capercaillie (Quevedo et al. 2006b). The circular plots
contained varying proportions of the different types of
habitat. This presented analytical difficulties due to the
fact that the proportion of a given habitat was not independent of the other habitats in the plot, and the sum was
1. Let xi be the proportion of the plot area occupied by a
given habitat type i. To avoid the unit-sum constraint, we
transformed the proportion of each habitat type xi by
using the centred log-ratio transformation yi = ln (xi/
xmean), being xmean the mean value of the proportions of
the different habitat types in each plot. These transformed
variables are linearly independent of each other, and are
commonly used to analyse compositional data like ours
(Aebischer et al. 1993). Thus, for each capercaillie
observation, we derived four independent habitat variables
scaled to the area of the plots: boks (proportion of beech
or oak forest), birs (birch forest), shrs (shrubs), opens
(pastures and open areas), where the s subscript indicated
the area of the plot in hectares.
To obtain topographic information for capercaillie
locations we built a digital elevation model (DEM), of cell
size 0.01 ha, from 1:5,000 digital elevation contours (5 m
elevation interval). We derived slope and aspect from that
DEM and calculated the average values of slope and
northern exposure in a 0.09 ha neighbourhood (3 9 3
DEM cells) centred in each observation point. The elevation values of the observations in each discrete survey area
were standardized to avoid introducing an area effect into
the comparison among groups (hereafter std elevation).
To estimate northern exposure, we transformed aspect into
an index (north) ranging from 0 (maximum southern
exposure) to 1 (maximum northern exposure). Terrain
ruggedness (rug) was estimated by means of the standard
Table 1 Description of the four habitat types considered in this study, summarized from a high-resolution GIS database, to assess habitat
partitioning in Cantabrian capercaillie: (1) beech and oak forest, (2) birch forest, (3) woody shrubs, and (4) open areas (a.s.l. above sea level)
Habitat type (abbreviation) Description
Beech and oak forest (bok) Mostly old-growth forest dominated by beech and oak, with interspersed patches of secondary growth, from about
700–1,300 m a.s.l. Understorey sparse and patchy, including great wood-rush (Luzula sylvatica), bilberry and tree
heath (Erica arborea)
Birch forest (bir)
Birch-dominated forest, mostly forming the tree line and located on fresher exposures. These are mainly thicket-like
patches with thin, twisted and multi-stemmed birch trees and a well-developed layer of bilberry and tree heath
Woody shrubs (shr)
Areas dominated by shrubs of variable heights up to 3 m, mainly brooms (Cytisus sp., Genista sp.) and heaths
(Erica arborea and Calluna vulgaris) sometimes mixed with patches of bilberry, in well-preserved upland areas.
E. aragonensis might be replacing the former species in a few burned areas at lower altitudes
Open areas (open)
Mountain pastures and scree slopes mostly situated above the tree line but also interspersed within forest patches at
lower altitude
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Table 2 Description of the variables considered in the analysis of habitat partitioning in Cantabrian capercaillie
Abbreviation
Description
boks(1–78)
Centred log-ratio transformation of beech or oak forest cover (%) in plots of area s around observations
birs(1–78)
Centred log-ratio transformation of birch forest cover (%) in plots of area s around observations
shrs(1–78)
Centred log-ratio transformation of shrub cover (%) in plots of area s around observations
opens(1–78)
Centred log-ratio transformation of open areas and meadow cover (%) in plots of area s around observations
std elevation
Mean elevation in a 9 ha neighbourhood centred in each observation, standardized to the mean altitude
rug
SD elevation (m a.s.l.) in a 9 ha neighbourhood centred in each observation
slope
Mean slope (%) in a 9 ha neighbourhood centred in each observation
north
Mean northern exposure (index ranging 0–1) in a 9 ha neighbourhood centred in each observation
deviations of the elevation in the 0.09 ha neighbourhood
around each observation (Table 2).
multinomial logistic regressions, alternating the response
category until all comparisons had been completed.
Habitat partitioning
Habitat suitability
To analyse habitat characteristics and to assess capercaillie
habitat partitioning, we used multinomial logistic regressions (logit link, nnet package, R Development Core Team
2006), an iterative method based on maximum likelihood
estimation (Agresti 2002). This analysis handles continuous or discrete explanatory variables and categorical
response variables with more than two levels or categories.
We assimilated the type of observation [(1) hens with
broods in summer, (2) broodless hens in summer, (3) cocks
in summer and (4) cocks in display sites in spring] to a
categorical response variable with four categories. The
explanatory variables were topographic (std elevation,
north, rug) and vegetation characteristics of the habitat
(boks, birs, shrs, opens).
Variables were considered explanatory a priori according to the following criteria: (1) significant relationship
with capercaillie habitat partitioning (P \ 0.1) in univariate multinomial logistic regressions; (2) Pearson’s
correlation coefficient with the other explanatory variables
lower than 0.6. To build the minimal adequate model, we
followed a step-up procedure by fitting univariate models
that were retained at a \ 0.1. We retained the univariate
model with the lowest Akaike information criterion (AIC,
Burnham and Anderson 1998), which trades-off goodness
of fit of the model against its complexity. We then proceeded to test bivariate models, retaining the one that
yielded the lowest AIC. The process ended when addition
of new variables did not reduce the AIC any further.
Thereafter, we tested for non-linearity and interaction
effects by adding quadratic and product terms to the minimal adequate model. In multinomial logistic regression,
one category of the response variable is chosen as the
comparison category. We performed a series of
We used an existing habitat suitability map for capercaillie
in the area (Quevedo et al. 2006a) to compare the predicted
habitat suitability corresponding to sightings of hens with
broods, cocks and broodless hens at the landscape scale.
This habitat suitability map was developed from a logistic
model, using the information of display grounds, so that the
characteristics of presence areas (i.e., occupied leks) and
absence areas (i.e., abandoned leks) were compared in a
grid of 25 ha habitat units. See Quevedo et al. (2006a) for
details on model construction and suitability maps. The
model merged both natural and anthropogenic factors as
relevant in determining the probability of capercaillie
occurrence and identified the spatial scale of their effects.
The proportion of forest cover in a local 25 ha habitat unit,
the proportion of forest cover in a 50 km2 neighbourhood,
and the degree of northern exposure of the local habitat unit
had positive effects on the probability of capercaillie
presence, whereas the number of human settlements had a
negative effect, most significant in a 28 km2 neighbourhood. From a combination of those variables and their
relative effects, a map of habitat suitability was derived as
a conservation tool so that areas classified as highly suitable for capercaillie indicate areas of special interest. Since
the model and the subsequent suitability map were built on
the basis of display grounds, the question remains whether
other sectors of the population are properly represented.
Should brooding hens be located in areas predicted as
highly suitable for capercaillie in the map, protection
measures on such areas would also benefit this important
group of the population. To check this, we compared the
values of predicted habitat suitability and the values of the
explanatory variables from the model for the locations of
hens with broods, cocks, broodless hens and display
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Table 3 Average values of
main habitat features for
Cantabrian capercaillie at spring
and summer locations. For land
cover variables, only the most
relevant scale (78 ha) is shown.
See Tables 1, 2 and Methods for
a comprehensive explanation of
each variable
249
Explanatory variables Spring
Display areas (115) Hens with broods (24) Cocks (95)
1.13 ± 0.03
1.05 ± 0.07
1.19 ± 0.03
1.05 ± 0.05
bir78
0.31 ± 0.03
0.40 ± 0.08
0.21 ± 0.03
0.29 ± 0.04
shr78
0.65 ± 0.04
0.64 ± 0.07
0.57 ± 0.03
0.65 ± 0.04
open78
0.19 ± 0.02
0.28 ± 0.06
0.34 ± 0.03
0.35 ± 0.03
elevation
1,308 ± 16
std elevation
-0.13 ± 0.11
1,378 ± 30
1,377 ± 30
1,402 ± 19
0.39 ± 0.50
0.005 ± 0.11
3.9 ± 0.1
4.1 ± 0.2
4.2 ± 0.1
4.6 ± 0.2
slope
25.6 ± 0.7
26.3 ± 1.2
26.5 ± 0.6
28.6 ± 0.8
north
0.71 ± 0.02
0.77 ± 0.03
0.76 ± 0.02
0.78 ± 0.02
grounds using pairwise t-tests or Mann–Whitney tests,
depending on the distribution of the variables.
Results
Summer sightings of capercaillies along the study period
corresponded to 95 cocks and 93 hens. Only 24 (26%) of
those hens were accompanied by one or more juveniles.
There was an average of 0.54 juveniles per hen, a mean
brood size of 2.2 (range 1–7), and 69 (74%) broodless hens.
Three vegetation and two topographical variables
emerged as a priori explanatory variables for the habitat
partitioning model: open78, bok78, bir78, rug, and north.
Although other variables showed higher values in summer
(Table 3), the differences were not significant. The proportion of open areas in a 78 ha neighbourhood (open78)
showed the best fit to habitat partitioning and, thus, was
entered first into the multinomial logistic model (Table 4).
All summer groups showed higher open78 values than did
spring display areas (Tables 3, 5). The second variable to
be entered into the final model was ruggedness (rug,
Table 4). Broodless hens were located in more rugged
terrain than cocks and spring display areas (Tables 3, 5).
The third and last variable to be entered into the final
model was the proportion of beech and oak forest (bok78,
Table 4). bok78 showed that cocks preferred sites with a
Table 4 Summary of the step-up model selection procedure for the
multinomial logistic model of habitat partitioning between hens with
broods, broodless hens, cocks and spring display areas of Cantabrian
capercaillie (RD residual deviance, AIC Akaike information criterion,
df degrees of freedom)
RD
Broodless hens (69)
bok78
rug
Parameter
Summer
AIC
v2
df
P
Null model
739
744
–
–
–
open78
711
723
28.0
3
\0.001
open78 + rug
693
711
46.0
6
\0.001
open78 + rug + bok78
684
708
55.1
9
\0.001
0.12 ± 0.15
higher proportion of beech and oak forest than the sites
preferred by hens with or without broods. Adding aspect
(north) and the proportion of birch forest (bir78) did not
further improve the performance of the model, although
these variables yielded significant results in univariate
tests: hens with broods and spring display areas were more
closely associated with birch forest than cocks in summer,
and broodless hens were located in areas with a more
pronounced northern orientation than spring display areas
(Tables 3, 6).
Hens with broods were located in areas with higher
habitat suitability than cocks or broodless hens according
to the suitability map (pairwise t-tests, P \ 0.05, Fig. 2).
The main explanatory variable driving the habitat suitability model was the proportion of forest cover in a 50 km2
neighbourhood. At this landscape scale, hens with broods
and cocks both showed preference for a significantly higher
proportion of forest cover than broodless hens (pairwise ttest, P = 0.009 and P = 0.011, respectively).
Discussion
The summer habitat of Cantabrian capercaillie differed
from the much better known habitat in spring display areas,
showing the increased importance of open areas. We found
habitat partitioning among groups of birds, indicating that
habitat partition in capercaillie might be found at broad
spatial scales and in highly fragmented, patchy habitats.
Hens with broods showed a clearer association with treeline birch forests, whereas cocks were preferentially
located in beech or oak forests. Some topographic features
also differed among groups: broodless hens were located in
summer in more northern and rugged exposures than were
cocks. Shifting up the spatial scale of analysis, we found
that hens with broods were located in the most suitable
areas for the species according to a previous habitat suitability map, mainly characterized by high proportion of
forest cover at large spatial scales (Quevedo et al. 2006a).
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250
Table 5 Coefficients of the
three explanatory variables
entering the minimal
multinomial regression model
of habitat partitioning for
Cantabrian capercaillie. The
sign of the coefficients refers to
the group in the left column
(e.g., values for open78 are
significantly lower for display
areas than for hens with broods)
J Ornithol (2008) 149:245–252
open78
Hens w. broods
Hens w. broods
–
Table 6 Coefficients of bir78
and north in univariate
multinomial regression models
of habitat partitioning for
Cantabrian capercaillie. The
sign of the coefficients refers to
the group in the left column
(e.g., values for bir78 are
significantly lower for cocks
than for hens with broods)
*** P \ 0.001, ** P \ 0.01, *
P \ 0.05
1.31 ± 0.97
–
Cocks
1.03 ± 0.94
-0.28 ± 0.61
–
-3.50 ± 0.76***
Broodless hens
-3.23 ± 0.70***
Cocks
Display areas
Display areas
rug
-2.20 ± 1.01*
Hens w. broods
Hens w. broods
–
Broodless hens
0.37 ± 0.21
Cocks
0.09 ± 0.20
-0.28 ± 0.14*
–
Display areas
-0.22 ± 0.20
-0.58 ± 0.15***
-0.30 ± 0.13*
–
Display areas
–
Cocks
Display areas
–
Hens w. broods
Broodless hens
Hens w. broods
–
Broodless hens
0.10 ± 0.66
Cocks
1.53 ± 0.69*
1.43 ± 0.54**
–
Display areas
0.56 ± 0.88
0.46 ± 0.48
-0.97 ± 0.51
–
bir78
Hens w. broods
Broodless hens
Cocks
Display areas
Hens w. broods
–
–
Broodless hens
-0.82 ± 0.64
–
Cocks
-1.66 ± 0.65*
0.84 ± 0.50
–
Display areas
north
-0.66 ± 0.61
Hens w. broods
0.16 ± 0.46
Broodless hens
1.00 ± 0.46*
Cocks
Hens w. broods
–
Broodless hens
0.55 ± 1.31
Cocks
-0.23 ± 1.23
-0.78 ± 0.90
–
-1.47 ± 1.20
-2.02 ± 0.85*
-1.23 ± 0.71
Overall, in summer, capercaillie were sighted closer to
forest edges than to spring display grounds, as evidenced
by the increased importance of open areas in their
–
Display areas
–
Display areas
Fig. 2 Habitat suitability values (mean ± 2 SE) in the 25 ha habitat
units containing display grounds in spring, and summer locations of
cocks, broodless hens, and hens with broods, according to a habitat
model developed for Cantabrian capercaillie (Quevedo et al. 2006a).
Different letters above the symbols indicate significant differences in
pairwise t-tests (P \ 0.05)
123
Cocks
Broodless hens
bok78
*** P \ 0.001, ** P \ 0.01, *
P \ 0.05
Broodless hens
–
surroundings. These open areas corresponded mainly to
upland habitats, but also to smaller patches of scree and
herbaceous gaps within the forest. Although the forest was
still the most relevant habitat for all groups during the
summer, the association was stronger for cocks, resembling
the habitat partitioning found in Scandinavian capercaillies
(Rolstad et al. 1988). That is also the case in the Pyrenees,
where cocks are mostly associated with the forest in
summer whereas hens are found in treeline habitats, near
upland meadows and subalpine moors (Menoni 1990).
Differences in requirements and habitat use are not
surprising in capercaillie, the largest and most dimorphic
grouse, and should be incorporated into conservation plans.
The mechanism for this habitat partitioning may be connected to differences in life history. Although females are
less conspicuous than cocks, in terms of both appearance
and behaviour, they are potential prey for a wider range of
predators because of their smaller size and their reproductive behaviour during the nesting and chick-rearing
periods. Together with the high demands of energy of
J Ornithol (2008) 149:245–252
chicks, this suggests that brood-rearing hens, which need
good refuges and optimal food resources, would have the
most restrictive habitat requirements. In our study, hens
with broods showed a stronger association with birch forest
than did cocks. In the Cantabrian Mountains, this habitat is
usually characterized by a rich understorey of ericaceous
shrubs, such as tree heath and bilberry, which provide
abundant food and refuge. In addition, bilberry plants are
taller and grow faster in birch-dominated tree lines than
within denser and shadier oak and, especially, beech forests
(Fernandez-Calvo and Obeso 2004).
The combination of results at local and regional scales
highlights the importance of preserving tracts of intact
ecosystems, and generalizes a previous habitat suitability
model to predict good brood-rearing areas. The relatively
high values of habitat suitability found for brooding hens
were mainly due to higher proportion of forest cover in a
neighbourhood of 50 km2. This suggests that high suitability areas pinpoint the last locations where capercaillie
reproduction can effectively take place within the ongoing
process of population decline. These areas would constitute
refuges, broadly understood as including better choices in
terms of feeding, competition, predation and shelter,
among several other relevant aspects for the survival of a
population (Berryman et al. 2006). This idea is consistent
with previous results that indicated an indirect relationship
between the habitat configuration in the Cantabrian
Mountains and the ongoing process of capercaillie decline
(Quevedo et al. 2006a).
This unique capercaillie population has been studied and
managed largely from a lek-centred perspective. This has
somewhat neglected the importance of habitats other than
old forest, such as gaps or treeline habitats with rich heath
cover, which could be important in other stages of the
capercaillie’s life cycle (Quevedo et al. 2006b). Our results
help to fill the gap, and we hope they will sustain betterinformed habitat management and aid the enforcement of
habitat protection. Our results also provide further evidence
that treeline and generally upland habitats should not be
forgotten in the conservation of the Cantabrian Mountains
(Naves et al. 2006), a region where both forest fragmentation and anthropogenic pressure are very high (Garcı́a
et al. 2005; Quevedo et al. 2006a). From a more general
perspective, these results highlight the need to consider
different sectors of a population and different spatial scales
in conservation practices.
This study does not include hard data about nesting and
early brooding periods, which may have different
requirements. However, obtaining significant information
on these aspects of capercaillie life cycle in the Cantabrian
Mountains seems difficult, both due to the ruggedness of
the terrain and the low density of birds. Also, the disturbance associated with any study involving breeding hens
251
might be detrimental to a highly endangered population
such as this one, and its potential advantages and drawbacks should be carefully considered.
Zusammenfassung
Habitataufteilung beim bedrohten Kantabrischen
Auerhuhn Tetrao urogallus cantabricus
Das bedrohte Kantabrische Auerhuhn lebt am südlichen
Rand des Verbreitungsgebiets der Raufußhühner in sommergrünen Laubwäldern. Die Planungen für die Erhaltung
dieser Art haben sich immer auf die Arenabalz konzentriert. Es gibt nur wenig Information über die spezifischen
Habitatbedürfnisse von Hennen und Bruten, und das obwohl der Fortpflanzungserfolg ein limitierender Faktor zu
sein scheint. Wir haben Sommererfassungen von 1997 bis
2004 analysiert, die durchgeführt worden waren, um den
Fortpflanzungserfolg der Population abzuschätzen. Wir
haben die Habitatkennzeichen bei unterschiedlichen Raumgrößen für Hennen mit Bruten, Hennen ohne Bruten und
Hähne im Sommer mit dem besser bekannten Frühlingshabitat in Balzarenen verglichen. Das Sommerhabitat wies
einen höheren Anteil offener Flächen auf und war mit
stärker zerklüfteten Zonen mittlerer Raumgröße (78 ha)
assoziiert als das Frühlingshabitat in Balzarenen. Hähne
und Hennen zeigten im Sommer Habitataufteilung; Hennen
waren mit höheren Anteilen offenen und buschigen Habitats assoziiert. Außerdem bevorzugten Hennen ohne Bruten
Flächen mit höherer Hangneigungsvariabilität als Balzarenen und von Hähnen bevorzugte Sommerflächen. Diese
Unterschiede könnten den Sexualdimorphismus in Fortpflanzung, Energiebedarf und Auffälligkeit bei dieser Art
widerspiegeln. Bei ausgedehnteren Raumgrößen funktionierte ein zuvor entwickeltes Habitateignungsmodell gut,
um günstige Brutaufzuchtsplätze vorherzusagen. Hennen
mit Bruten waren in den am besten geschützten Flächen
des Gebiets zu finden, die hauptsächlich durch höhere
Anteile an Waldbedeckung in großem Maßstab (50 km2)
charakterisiert waren. Wir schlagen vor, dass diese
Eigenschaften Refugienhabitate anzeigen, in denen
Kantabrische Auerhühner noch erfolgreich brüten können.
Acknowledgements We thank the Asturian Environmental Agency
(Consejerı́a de Medio Ambiente del Principado de Asturias), and
specifically Alejandro González and Orencio Hernández, for providing access to the original technical reports of the summer capercaillie
drives. We also thank José Luis Benito, the coordinator of the summer
drives and author of corresponding technical reports. Alberto Fernández-Gil, José Carral, Fernando Rodrı́guez Pérez and Victor Vega
provided additional summer data. We are especially grateful to the
forest rangers of the Asturian environmental authority with whom we
have collaborated for several years. We also thank Fernando González Taboada, for statistical discussion, and Alberto Fernández-Gil,
123
252
for a thoughtful review of the manuscript. Christine Francis edited the
English. This study was funded by a grant (CN-05-018) from the
Asturian Environmental Agency to J.R. Obeso.
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