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Habitat selection of the Eurasian woodcock in winter in
relation to earthworms availability
Olivier Duriez
a,b,*
, Yves Ferrand
c,**
, Franc¸oise Binet
d
, Eve Corda
c
,
Franc¸ois Gossmann
e
, Herve
´Fritz
f
a
Laboratoire dÕEcologie, UMR 7625, ba
ˆtiment A, 7e
´me e
´tage, case 237, 7 quai St Bernard, Universite
´Paris 6, 75005 Paris, France
b
Office National de la Chasse et de la Faune Sauvage, CNERA Avifaune Migratrice, Station de Chize
´,
Beauvoir-sur-Niort, 79360 Villiers-en-Bois, France
c
Office National de la Chasse et de la Faune Sauvage, CNERA Avifaune Migratrice, 5 rue de St-Thibaut,
BP 20 St-Benoist, 78612 Le-Perray-en-Yvelines cedex, France
d
CNRS – Universite
´de Rennes I, UMR 6553, Ecobio 263 avenue du Ge
´ne
´ral Leclerc, Campus de Beaulieu, Ba
ˆt 14B, CS 74205,
35042 Rennes Cedex, France
e
Office National de la Chasse et de la Faune Sauvage, CNERA Avifaune Migratrice, 53 rue Russeil, 44000 Nantes, France
f
CNRS – Centre dÕEtudes Biologiques de Chize
´, UPR 1934, BP 14, 79360 Beauvoir-sur-Niort, France
Received 27 February 2004; received in revised form 20 July 2004; accepted 5 August 2004
Abstract
The Eurasian woodcock (Scolopax rusticola) is a game species experiencing high hunting pressure, long-term modifications of its
habitats, and with questions regarding its current conservation status. Winter is a season of highest concentration of birds and hunt-
ing pressure but woodcock precise habitat requirements are poorly known. It is crucial to assess threats and to develop sustainable
management options for the conservation of woodcock populations. During three consecutive winters, we monitored 65 individual
woodcocks fitted with radio-tags in Brittany, France. Habitat selection was analysed using GIS and compositional analysis, in rela-
tion to vegetation types, soil variables (humus types) and the abundance of their main prey (earthworms). Woodcocks used different
habitats diurnally and nocturnally, generally preferring areas with high earthworm biomass. Diurnal habitat selection in forests was
associated with humus type (preference for mulls, rich in earthworms) and dense shrub strata (better protection). Hedges with a high
density of trees and shrub were also important habitat. At night, grazed meadows were the preferred habitat, containing five times
higher biomass of earthworms compared to cultivated fields. Sustainable management of populations requires protection and man-
agement of habitats that incorporates food and cover. Forestry practices should preserve rich humus types and coppices by choosing
tree species that ameliorate the soil and soil tilling. Changes in landscapes and intensive agricultural practices are current threats to
woodcock populations: destruction of hedges, decrease of permanent grazed meadows, impoverishment of soils fauna biomasses
from ploughing and chemical applications. However, woodcocks may benefit from the recent development of set-asides, grass
field-borders and simplified farm practices (no-tillage and direct sowing).
2004 Elsevier Ltd. All rights reserved.
Keywords: Compositional analysis; Lumbricidae; Habitat changes; Scolopax rusticola; Sustainable management
1. Introduction
In Europe, many wildlife populations associated with
traditionally farmed landscapes declined with changes in
agricultural policies and farming practices (Pain and
0006-3207/$ - see front matter 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biocon.2004.08.011
*
Corresponding authors. Tel.: +33 5 65 60 77 40
**
Fax: +33 1 30 46 60 99.
E-mail addresses: o.duriez@wanadoo.fr (O. Duriez), y.ferrand@
oncfs.gouv.fr (Y. Ferrand).
www.elsevier.com/locate/biocon
Biological Conservation 122 (2005) 479–490
BIOLOGICAL
CONSERVATION
Pienkowski, 1997; Aebischer et al., 2000). These large
scale spatial changes in human land use reduces biodi-
versity (Robinson and Sutherland, 2002). For example,
the changes in agricultural practices caused little bus-
tards (Tetrax tetrax) and skylarks (Alauda arvensis)to
decline drastically in most areas of Europe (Chamber-
lain et al., 1999; Wolff et al., 2001). Similarly, the Eura-
sian Woodcock (Scolopax rusticola L.) is likely to suffer
from agricultural and forestry changes, especially in
winter, when it uses habitats that are declining in Eur-
ope, especially its nocturnal habitats.
Woodcocks are mostly migratory birds, breeding in
Northern and Eastern Europe and wintering in large
numbers in western France (Fadat, 1991). Their conser-
vation status is poorly known on breeding grounds.
They are atypical among waders, being solitary, living
inland, and nocturnal in winter (Piersma et al., 1996).
Woodcocks are specialist predators of soil macrofauna:
in winter, earthworms constitute about 85% of wood-
cocksÕdiurnal energy intake and probably even more
at night; the rest being arthropods (insect: larvae and
imagoes; myriapods) and slugs (Granval, 1987). In win-
ter, woodcocks use three types of habitats: woodlands
and hedges during the day and fields and meadows at
night (Cramp and Simmons, 1983; Hirons and Bick-
ford-Smith, 1983; Wilson, 1983; Gossmann et al.,
1988; Granval and Bouche
´, 1993). Although wooded
areas are increasing overall in the European Union, it
is mostly in the form of conifer plantations (Colombet
et al., 1996; Sondag, 2003). The disappearance of hedges
is more dramatic. In France, 60% of hedges (740,000
km) was destroyed between 1966 and 1996 (Schmutz
et al., 1996), and the trend is similar in the rest of the
European Union (Pain and Pienkowski, 1997; Robinson
and Sutherland, 2002). The situation for meadows and
wet grasslands is similar because most of these habitats
have been converted to crop fields since the late 1950s
(Pain and Pienkowski, 1997; Wakeham-Dawson and
Smith, 2000). Between 1975 and 1995, 12% of the natu-
ral meadows and pastures disappeared from nine Euro-
pean countries (Poiret, 2003). The decrease in grazing
cattle and the wider use of nitrogen fertilisers enables
less fertile land to be farmed, allowing farmers to con-
vert these old meadows into arable fields or woodlands
(Potter, 1997; Vickery et al., 2001).
In addition to habitat changes, woodcocks are hunted
in most European countries. Hunting occurs mostly in
winter, when populations are concentrated. French
hunters kill 30–40% of the total harvest in Europe
(about 1,200,000 woodcocks) and the interest for wood-
cock hunting has recently increased (Ferrand and Goss-
mann, 2000). Currently, there is no clear trend in
woodcock populations but the very low survival rates
calculated from the French ringing data base is a con-
cern (Tavecchia et al., 2002). These threats lead conser-
vationists to give the Eurasian woodcock a ‘‘vulnerable’’
status in winter (Tucker and Heath, 1994; Heath et al.,
2000) although it was recently revised to ‘‘stable’’ (Wet-
lands International, 2002), following a recommendation
of European management plan (Office National de la
Chasse, 1998).
In this proposal, management plans must be prepared
for sustainable use and conservation of woodcock popu-
lations in winter, as well as the establishment of hunting-
free reserves. Designing sound management schemes
requires improved knowledge of wintering ecology and
behaviour of this species. The first step is to understand
mechanisms that determine habitat selection in winter.
Are woodcocks more constrained by the declines of pas-
tures, hedges, or by the changes in the forestry practices?
How does resource availability influence habitat selec-
tion? Previous studies of habitat selection used pointing
dogs, bag statistics (Imbert, 1988), or habitats pros-
pected during ringing (Ferrand and Gossmann, 1988;
Granval and Bouche
´, 1993) and were biased by the
behaviours of the dog, the hunter, or the ringer. Radio-
telemetry can provide more rigorous and detailed data
on winter habitat selection by woodcock, avoiding
human biases (Kenward, 2001). Only three pilot studies,
based on three radio-tracked individuals in Ireland (Wil-
son, 1983), five and eight individuals in Cornwall (Hirons
and Bickford-Smith, 1983; Hoodless, 1994) had focused
on winter habitat selection in the Eurasian woodcock.
In this paper, we examine diurnal and nocturnal hab-
itat selection in winter, with a large sample of radio-
tagged woodcocks. We first investigated habitat selec-
tion in a relatively undisturbed landscape, offering a
large proportion of traditional habitats, with limited
hunting pressure because of the hunting-free reserve sta-
tus of the main forest complex. Humus type indicates
how organic matter (leaf litter) is decomposed and
mixed to the mineral fraction of the soil by soil fauna
(Frontier and Pichod-Viale, 1993) and therefore gives
information about the soil fauna present at each loca-
tion. Because soil characteristics are probably important
to understanding woodcock habitat selection, we also
investigated the influence of humus types and earth-
worms availability on habitat selection by woodcocks.
2. Methods
2.1. Study site
We collected data from December to April, during
three consecutive winters (1999–2000, 2000–2001 and
2001–2002, hereafter 2000, 2001 and 2002 winters,
respectively). The study was conducted in the Beffou for-
est (48300N, 328 0W) and the surrounding bocage, lo-
cated in Brittany, the main wintering region for
woodcocks in France (Fadat, 1991). The study area
was c. 1800 ha. The topography was composed of small
480 O. Duriez et al. / Biological Conservation 122 (2005) 479–490
hills and valleys (altitude range: 160–322 m). The bocage
was composed of small woods and fields (<1 ha) en-
closed by old woody hedges. Woodcock hunting has
been prohibited in the Beffou forest since 1995 but is al-
lowed in the surrounding woods and hedges. Winter cli-
mate in Brittany is oceanic: rainy and windy with mild
temperatures (mean 5 C).
2.2. Capture methods and radio-tracking
We captured woodcocks at night with a spotlight and
a landing net, as they fed in fields surrounding the forest
(Gossmann et al., 1988). We captured 37 woodcocks in
2000 (21 adults and 16 yearlings), 48 in 2001 (15 adults
and 33 yearlings) and 34 in 2002 (10 adults and 24 year-
lings). Birds were aged (adult or yearling) using wing
feather characteristics and moult status (Clausager,
1973). Each bird was fitted with a radio-transmitter
(TW3, Biotrack
, UK), weighting 7, 9 or 12 g (2–4%
of body mass) according to the battery size and presence
of activity tiltswitch (Duriez et al., 2004). In winter 2000,
radio-tags were secured on the back with a Teflon rib-
bon two-loop backpack harness (Kenward, 2001). Be-
cause seven woodcocks in 2000 were found dead of
starvation after the bill caught in the upper loop of the
harness, in winters 2001 and 2002, radio-tags were glued
on the back and secured with a single-loop wire harness,
passing around the belly and behind the wings (McAu-
ley et al., 1993). These seven birds were not included
in the rest of analyses.
Each bird was located 2–3 times per week during the
day and 2–3 times per week at night in winter 2000, until
departure, and 4–5 times per week in the following win-
ters. During the day, we approached woodcocks by cir-
cling to 10 m or less. Woodcocks did not leave diurnal
sites during the day or only moved by walking (usually
<100 m, personal observation). At night, woodcocks
were also approached by circling and located to the
nearest 50 m because they were more likely to fly, espe-
cially during clear moonlight nights. However the type
of field was determined each time. During seven nights
in 2001, we monitored 23 birds at 2-h interval. 80% of
birds stayed the entire night in the field chosen at the
beginning of the night and 89% within a radius of 150
m. Subsequently we located birds once per night.
2.3. Analysis of radio-telemetry data
We recorded each location on a habitat map using a
Geographic Information System (GIS; ArcView
3.2,
ESRI, Redlands, California, USA). This map was digi-
tised from an aerial photograph taken in 1992 (scale
1/10,000, source: Institut Ge
´ographique National). For
all analyses, we compared birds with similar numbers
of locations. The number of locations varied according
to the date of capture of the bird (December to mid Jan-
uary) and the date of end of monitoring (death or migra-
tion starting in the last decade of February). We only
used birds with at least 7 precise diurnal/nocturnal loca-
tions (limit fixed on a natural break in the data set) dur-
ing the study period which was limited to January and
February (excluding December with scarce locations,
and the pre-migratory period in March). Therefore, we
used a total of 2834 locations concerning 65 woodcocks
over the three years: 22 birds in 2000 (15 adults and 7
yearlings), 22 in 2001 (8 adults and 14 yearlings) and
21 in 2002 (7 adults and 14 yearlings). During the entire
study period, we only had 3 days of frost in January
2000 and 4 days in February 2001. Because several con-
secutive days of freezing ground changed the behaviour
and habitat selection of woodcocks (Hirons and Bick-
ford-Smith, 1983; Wilson, 1983), we excluded from the
analyses the data obtained during the days of frost be-
cause accurate analysis of habitat selection was not
possible.
2.4. Habitat selection analysis
We analysed habitat selection using compositional
analysis (Aitchison, 1986; Aebischer et al., 1993) where
the sample size was the number of tagged individuals
and radiolocations served to subsample each individ-
ualÕs habitat use. Since we restricted the period of study
in two months in order to limit the differences in loca-
tions between individuals, we did not weighed the com-
positional analysis by the number (or the square-root) of
radiolocations. In compositional analysis, the propor-
tions of habitats used by each individual were compared
to the proportions of habitats available. Analysis of
habitat selection on the basis of home ranges was not
appropriate in the case of the woodcock, because birds
made flights between diurnal and nocturnal habitats.
Hence ‘‘used’’ habitats associated with radiolocations
were compared with the habitats available in the study
area. ‘‘Available’’ habitats were calculated differently
according to the type of habitat (see below). Composi-
tional analysis is sensitive to the number of habitats
tested and Aebischer et al. (1993) suggest minimising
the number of different habitats. Thus we analysed first
with all detailed habitats and second with pooled habi-
tats by grouping habitats similar in structure. Composi-
tional analysis allowed a comparison of habitat selection
according to individual characteristics (age) and sea-
sonal effects (year of study) using MANOVAs.
2.4.1. Woodlands
The ‘‘woodland’’ habitat included the Beffou forest
(612 ha) and surrounding woodlands (c. 130 ha). The
amount of available habitat of each type was calculated
from the GIS map (Table 1). The stands in the Beffou
forest was diverse and contained nine habitat types
(Table 1). Deciduous stands (plantations, coppices and
O. Duriez et al. / Biological Conservation 122 (2005) 479–490 481
timbers) mostly contained Beech (Fagus sylvatica)and
Oak (Quercus robur and Q. sessiliflora), and some Ash
(Fraxinus excelsior). Coniferous stands (plantations
and timbers) were mostly Sitka spruce (Picea sitchensis),
Common silver fir (Abies alba), and Grant fir (A. gran-
dis). ÔPine timbersÕcontained Scots pine (Pinus sylvestris)
and Maritime pine (Pinus pinaster). In all habitats types,
the shrub strata contained Yew (Taxus baccata), Holly
(Ilex aquifolium), and Hazel (Corylus avelana). ÔWet for-
estsÕwere characterised by Willows (Salix sp.), Alders
(Alnus glutinosa) and Poplars (Populus sp.) and by the
presence of typical wetland plants (Greater tussock
sedges Carex paniculata and Common rushes Juncus
conglomeratus). For the pooled analysis, we kept six
habitat types. We kept Ôdeciduous timbersÕ,Ômixed tim-
bersÕand Ôwet forestsÕ, but other categories were pooled
as follows: Ôpine timbersÕwith Ôconiferous timbersÕ,Ôde-
ciduous plantationsÕwith Ôconiferous plantationsÕand
ÔcoppicesÕwith Ôcoppices-with-standardÕ.
Humus types depend on many factors: biotic (vegeta-
tion, soil fauna, macrofauna) and abiotic (nature of geo-
logic substrate, slope, hydrology). Consequently, humus
could change in short distances (within 10 m) and were
very difficult to map. Thus, ‘‘available’’ humus variables
were the proportions of each type of humus in a system-
atic sampling based on a 200 ·200 m grid covering the
entire forest and extended to several surrounding woods
(182 sampling points). Three types of humus were deter-
mined following Jabiol et al. (1995) (mors, characterised
by the accumulation of litter resulting from acid sub-
strate and scarcity of earthworms; mulls, characterised
by only a thin litter layer resulting from an active and
abundant soil fauna; and moders in the intermediate sit-
uation) and their proportions are given in Table 2.
Because shrub cover is probably an important param-
eter to provide cover for woodcocks during the day, the
proportion of shrub cover was estimated with a 10-m
tape (decametre) and the presence/absence of a shrub
was noted every 0.5 m. We calculated the % shrub cover
for each site as the ratio of the number of points with
shrubs to the total number of points (20). Shrub cover
was estimated from 82 sites randomly chosen from the
182 sites used for the humus availability survey, and
on 176 sites used by woodcocks (74 in 2000 and 102 in
2001).
Table 2
Proportions of the humus types in woodlands and hedges types in the
study area in Brittany, France
Habitat type Code Number of points %
Humus
Mor 24 13.2
Moder 61 33.5
Mull 97 53.3
Hedges
Wooded with strip WS 30 33.7
Wooded without strip W 27 30.3
Shrub with strip SS 13 14.6
Shrub without strip S 10 11.2
Relictual R 9 10.1
The proportions of each type were considered as the same in the three
years. Humus types were estimated from a systematic sampling of 182
sites and hedges were estimated from a random sampling of 89 sites
(see text).
Table 1
Description of the habitat types in the study area, comprising the Beffou forest and the surrounding woods and fields in Brittany, France
Habitat Code Area (ha) %Description
Woods
Deciduous plantations DP 191 25.2 2–4 m, 10–15 years, Abundant shrub and grass strata
Coniferous plantations CP 21 2.8 2–4 m, 10–15 years, Abundant shrub and grass strata
Coppices COP 60 7.9 5–10 m, 15–30 years, Abundant shrub and grass strata
Coppices-with-standard CWS 55 7.3 15–30 m, 30–60 years, Abundant shrub and grass strata
Deciduous timber DT 165 21.8 15–30 m, 40–120 years, Shrub and grass strata limited or absent
Mixed timber MT 71 9.3 15–30 m, 40–120 years, Shrub and grass strata limited or absent
Pine timber PT 14 1.8 15–30 m, 40–120 years, Shrub and grass strata limited or absent
Coniferous timber CT 148 19.6 15–30 m, 40–120 years, Shrub and grass strata limited or absent
Wet forest WF 32 4.2 Various height, age and shrub strata, aquatic plants, saturated soil
Total woods 756 100
Fields
Seed plots SP 135 13.0 Grass or winter wheat, vegetation 5–10 cm, bare soil
Stubbles ST 176 17.0 Corn or wheat (or mustard), bare soil
Young grazed meadows YGM 47 4.5 <3 years, Sowing furrows still visible, regular structure, vegetation <15 cm
Dry grazed meadows DGM 441 42.5 3–10 years, Sowing furrows not visible, irregular structure, vegetation <15 cm
Wet grazed meadows WGM 58 5.5 Permanent, vegetation <15 cm, aquatic plants, saturated soil
Un-grazed meadows UM 178 17.5 No trace of grazing, vegetation >15 cm, dry or saturated soil
Total fields 1035 100
Total study zone 1791
The area (in hectares) and % (in italics) of each habitat are given as means for each of the three years of study.
482 O. Duriez et al. / Biological Conservation 122 (2005) 479–490
2.4.2. Hedges
Because it was impossible to map the characteristics
of every hedge in the study zone (more than 200 km
of hedges), we randomly sampled 89 50-m sections of
hedges to determine the availability of each type of
hedge. Differences in computation of habitat availability
between forest habitats and hedges (area vs. proportion)
precluded any combination of the two habitats in the
same analysis. Hedges were constituted by trees and
shrubs growing on an embankment. Hedge had four
vegetation strata: (1) the tree strata (7–20 m), mostly
beeches and oaks; (2) the shrub strata (1–7 m), mostly
Hazels, Gorse (Ulex europaeus), Broom (Cytisus scopa-
rius); (3) the grass strata (<1 m); (4) an edge strata (lat-
eral strip), which was the lateral extension of the hedge
into the meadow (not on the embankment, 0.3–3 m
wide) and contained mostly brambles, brackens, grass
and branches and sometimes shrubs. For the pooled
analysis, hedges were divided into three types: Ôwooded
hedgesÕwith tree, shrub and grass strata; Ôshrub hedgesÕ
with shrub and grass strata; and Ôrelictual hedgesÕwith
only the grass strata (Table 2). For the detailed analysis,
we also analysed the presence/absence of the lateral
shrub strip and we kept five types of hedges: Ôwooded
with stripÕ,Ôwooded without stripÕ,Ôshrub with stripÕ,
Ôshrub without stripÕand ÔrelictualÕ(always without
strip) (Table 2).
2.4.3. Fields
Nocturnal ÔfieldÕhabitat included c. 1200 land par-
cels. We calculated area of each type of available habitat
from the GIS (Table 1). Meadows represented 70% of
the fields and were divided in three types: young mead-
ows, old dry meadows, and permanent wet meadows. A
meadow was characterised as ÔgrazedÕif it showed actual
or recent grazing with cow dungs, footprints and short
vegetation. Tall grass identified Ôun-grazed meadowsÕ,
which included meadows that had not been grazed for
the six previous months, meadows for mowing and old
wet set-asides. Other fields included Ôseed plotsÕ(wheat
and grass) and ÔstubblesÕ(corn and wheat). For the de-
tailed analysis, the six habitats were: Ôyoung grazed
meadowsÕ,Ôdry grazed meadowsÕ,Ôwet grazed meadowsÕ,
Ôun-grazed meadowsÕ,ÔstubblesÕand Ôseed plotsÕ. For the
pooled analysis, four habitats were kept: Ôgrazed mead-
owsÕ(young, dry and wet), Ôun-grazed meadowsÕ,Ôstub-
blesÕand Ôseed plotsÕ.
2.5. Earthworm sampling
We sampled earthworms using the standardised
method described by Bouche
´and Gardner (1984) and
Bouche
´and Aliaga (1986). This method is a combina-
tion of two complementary extraction techniques: a
chemical extraction by 0.4% formalin application to ex-
pel active earthworms from the deep soil to the soil sur-
face, and a physical extraction by hand-sorting soil cores
(30 ·30 ·10 cm) to collect additional earthworms that
did not respond to the chemical extraction. Earthworm
sampling was performed in both diurnal and nocturnal
sites used by woodcocks (i.e., woodlands and fields)
from January to March 2001 and 2002. To select a plot
for earthworm sampling, we flushed a radio-tagged
woodcock (which usually returned to the same site on
the following day), in early morning (around 09:00) in
diurnal sites and at dark (around 20:00) in nocturnal
sites. We avoided samplings during freezing weather,
in very wet soils (no effect of formalin application), in
young wheat or grass seed plots (to prevent trampling
on crops) and in un-grazed meadows (not used by
woodcocks).
Because earthworm populations are highly aggre-
gated in patches (Poier and Richter, 1992; Rossi et al.,
1997), earthworm formalin extraction was done on an
area of 6 1-m
2
plots (3 1-m
2
spaced 10 m apart in a tri-
angle at the woodcock place and 3 other 1-m
2
plots in a
place randomly chosen 50 m apart) to take into consid-
eration the variability of the horizontal distribution of
earthworms biomass. Then, within each of the 6 plots,
2 soil cores (30 ·30 ·10 cm) were dug and hand-sorted.
Because some earthworms perform nocturnal migra-
tion and emerge from the soil at night (Lee, 1985), earth-
worm biomass available to woodcocks should be higher
at night than during the day. Hence, we slightly modi-
fied the sampling procedure for nocturnal habitats to
investigate about the earthworm biomass available to
woodcocks in the first 10 cm of soil, at night in fields.
After flushing a radio-tagged bird, we placed 6 1-m
2
plots similarly as for daytime sampling in forest. One
soil core (30 ·30 ·10 cm) was dug in each of the 6 plots
to measure the biomass of earthworms present in the
first 10 cm of soil. This soil core was kept in a trash
bag for future hand sorting in the following afternoon.
In the following morning, we moved the plots 1 m away
and performed the chemical extraction with formalin to
calibrate on the standard procedure of Bouche
´and Ali-
aga (1986). The nocturnal sampling procedure and cal-
culations are fully described in Duriez (2003).
For the two extractions (formalin and hand-sorting),
the earthworms collected were preserved in 4% formalin
prior to identification in the following months. All indi-
viduals were identified to species, counted and weighed
to the nearest 0.01 g (fresh mass). For each sampling
place, the earthworm biomass value was the mean of
the 6 square plots and was expressed as kg (fresh weight
worm) per hectare. We sampled a total of 38 sites in
fields and 43 sites in woodlands.
2.6. Statistical analyses
Means were reported ±1 standard deviation (SD) and
were compared with StudentÕst-tests or General linear
O. Duriez et al. / Biological Conservation 122 (2005) 479–490 483
models (GLM) with TuckeyÕs post-hoc tests, using SPSS
10.0 software (SPSS, 1999). To avoid pseudo-replication
(Hurlbert, 1984), we used General Linear Mixed Models
(GLMM) with individual as a random variable to give
the same weight to every individual, whatever the num-
ber of recordings (Littel et al., 1991). Normality of the
variables was assessed with the Kolmogorov–Smirnov
tests. We wrote a program for compositional analysis
for SPSS. As advised by Aebischer et al. (1993), a rand-
omisation test based on pairwise permutations was per-
formed to obtain an accurate p-value in compositional
analysis.
3. Results
3.1. Earthworm biomass
In fields, earthworms were more abundant and heav-
ier than in woodlands (number of individuals: 283 ± 199
wormsm
2
,n= 43 samplings in forest vs. 737 ± 390
wormsm
2
,n= 38 samplings in fields, t
53
=6.54,
P< 0.001; mass per individual worm: 0.085 ± 0.176 g,
n= 12,464 worms in forest vs. 0.397 ± 0.616 g,
n= 28,765 worms in fields; t
37,585
=78.87, P< 0.001).
Therefore, earthworm biomass was about 12 times high-
er in nocturnal field habitats than in diurnal woodland
habitats (Fig. 1;Table 3). In diurnal woodlands, the
earthworm biomass was four times higher in wet forest
and coppices, and to a lesser extent in recent plantations
than in the older stands (timbers) (Fig. 1;Table 3).
Among the humus types, earthworm biomass tended
to be higher in mulls than in moders and mors, although
it was not significant (Fig. 1;Table 3). In forest, earth-
worm sampling was slightly influenced by the month,
but not by the year nor the air temperature (Table 3).
There was no difference in earthworm biomass and its
spatial distribution between the three types of meadows
(young, dry and wet), but stubbles had 4–5 times less
earthworm biomass than meadows (Fig. 1;Table 3).
Earthworm sampling tended to be affected by air tem-
perature, but not by the month or the year (Table 3).
3.2. Diurnal habitat selection in woodlands and hedges
We used 59 of the 65 woodcocks in the analysis of
habitat selection in forest because the remaining 6 birds
spent most of their time in hedges and were located less
than 7 times in forest. Using the detailed classification
based on nine wood stands, habitat selection index k
was not highly significant (P= 0.037, Table 4). The
pooled classification of six forest stands showed prefer-
ences (P< 0.001). Plantations and coppices were the
most preferred habitats by woodcocks and timbers were
the least preferred. When considering soil humus types,
mulls were preferred to moders and mors (Table 4).
For forest stands as well as soil humus, there was no ef-
fect of year or age of woodcocks on their habitat selec-
tion (all P> 0.1). Mulls were present in 78% of
plantations, 70% of coppices and 50% of wet forests
(Fig. 2). Coniferous stands showed the highest propor-
tion of mors (30%), but they still contained similar high
proportion of mulls (30%).
Plantations, coppices and wet forests had more shrub
cover than older forest stands (Fig. 3; ANOVA
R
2
= 0.34, F
5,251
= 27.26, P< 0.001), and were richer in
earthworms. Percent shrub cover was higher in the 175
sites used by woodcocks compared to the 82 random
sites from systematic sampling (75.6 ± 27.2% vs.
57.7 ± 36.3%, respectively; GLMM on 44 individuals:
F
1,255
= 1040.11, P= 0.021).
Hedges were less frequented than woodlands: only
nine individuals that were located more than seven times
in hedges were analysed. In the detailed analysis, wooded
and shrub hedges with lateral shrub strip were preferred
over the other types (Table 4). The pooled analysis
showed that wooded hedges were preferred to shrub
day
woodland habitat and humus types
plant cop DT MT CT WF Mor Moder Mull mean
mean earthworm biomass (kg/ha)
0
50
100
150
200
forest stands
forest humus
Mean forest
15
8
42
8
6
5
12
25
43
night
field types
ST YGM DGM W GM mean
mean earthworm biomass (kg/ha)
0
200
400
600
800
1000
1200
1400
field types
Mean fields
6
4
22
6
38
Fig. 1. Earthworm biomasses (mean ± standard error SE in kg/ha) for
each diurnal (top) and nocturnal (bottom) habitat type used by
woodcocks (see Table 1 for labels). Numbers on the top of bars are the
number of sites sampled.
484 O. Duriez et al. / Biological Conservation 122 (2005) 479–490
Table 3
Factors influencing mean earthworm biomasses in different habitats (fields and forests) and at different levels (stands or humus types)
Analysis R
2
Factor Ftest df PInterpretation
Woods/fields 0.71 Habitat 175.51 1.73 <0.001 Fields > woods
Air temperature 3.10 1.73 0.084 Increase with temperature
Month 1.73 2.73 0.185
Year 0.09 1.73 0.767
Woods stands 0.33 Stand type 3.09 5.31 0.022 Cop = WF = plant > CF = DT > MT
Month 2.81 2.31 0.076 March > February > January
Year 0.31 1.31 0.580
Air temperature 0.10 1.31 0.921
Woods humus 0.28 Mull type 2.20 2.34 0.126 Mull > moder > mor
Month 1.79 2.34 0.182
Air temperature 0.60 1.34 0.444
Year 0.05 1.34 0.945
Fields 0.62 Field type 10.01 3.29 <0.001 Meadows > stubbles
Air temperature 4.08 1.29 0.053 Increase with temperature
Year 0.83 1.29 0.369
Month 0.47 2.29 0.628
Results are from GLM and the differences among groups were tested with TuckeyÕs post-hoc tests.
Table 4
Results of compositional analysis on habitat selection in wintering woodcocks
Analysis Group nWilkÕskPHabitat ranking
Woods stands Detailed 59 0.736 0.037 DP COP > CP > WF > PT > CWS > DT > CT > MT
Pooled 59 0.606 <0.001 Plantation coppice WF > coniferous timber > DT > MT
Woods humus Detailed 59 0.531 <0.001 Mull moder mor
Hedges Detailed 9 0.067 0.004 WS SS>W>S>R
Pooled 9 0.002 <0.001 Wooded shrub > R
Fields Detailed 63 0.273 <0.001 DGM ST > WGM > YGM UM > SP
Pooled 63 0.290 <0.001 Grazed meadows ST UM > SP
Diurnal habitat selection was analysed in woodlands (two levels: stands and humus) and in hedges, while nocturnal habitat selection was analysed in
fields. Habitats were ranked from the most preferred to the least preferred. A significant preference between two habitats was indicated by ‘‘’’ while
a non significant difference was indicated by ‘‘>’’ (Aebischer et al., 1993). The codes used for ranking of habitats are given in Tables 1 and 2.Pvalues
were given by randomisation.
PL COP DT MT CT WF
% of humus
0
20
40
60
80
100
54 22 35 15 46 10
Fig. 2. Proportions of humus types in the six types of woodland
habitats in the study area (black = mor, light grey = moder and dark
grey = mull). The proportions of humus are calculated on the
systematic sampling of 182 sites (the number of sites for each habitat
are given above the columns). Legend: PL = plantation; COP = cop-
pices; DT = deciduous timber; MT = mixed timber; CT = coniferous
timber; WF = wet forest.
% shrub cover
20 30 40 50 60 70 80 90 100
earthworm biomass (kg/ha)
0
20
40
60
80
100
120
140
160
Coppice Wet Forest
Plantation
Deciduous timber
Mixed timber
Coniferous timber
Fig. 3. Relationship between the percentage of shrub cover and
earthworm biomass (means ± standard error SE) in six habitat types in
woodlands. Values of percentage of shrub cover represent means ± SE
of 82 random sites and 175 sites used by woodcocks.
O. Duriez et al. / Biological Conservation 122 (2005) 479–490 485
and relictual hedges (Table 4). Year and age effects could
not be tested because sample size was too small.
3.3. Nocturnal habitat selection in fields
For the nocturnal habitats analyses, 63 woodcocks
were used and 2 were removed because they almost
never frequented the fields. We did not consider habitat
selection on nights when birds stayed in woodlands, be-
cause they were always located in the same habitat used
the previous day. Nocturnal habitat selection was differ-
ent from random use (P< 0.001) and dry grazed mead-
ows were preferred, followed by stubbles and wet and
young grazed meadows (Table 4). Un-grazed meadows
and seed plots were avoided. When the three types of
grazed meadows were pooled, they were the most pre-
ferred habitats. There was no effect of year or age in
any of the analyses (all P> 0.3).
4. Discussion
4.1. Diurnal habitat selection
Among the various types of woodlands, outside frost
period, woodcocks preferred young forest stands as hab-
itats: plantations, followed by coppices and wet forests.
Woodcocks avoided older stands of timber. Plantations
and coppices were characterised by an important shrub
strata, because more light reached the ground, while the
shrub strata was scarce in timbers. The shrub strata pro-
vides overhead protection from raptors and increases
cover from terrestrial predators. Preference for young
habitats in winter was suspected from the hunting statis-
tics (Imbert, 1988; Fadat, 1995) and woodcocks moni-
tored by Wilson (1983) almost exclusively used young
(20–30 years old) planted coniferous woodlands. Amer-
ican woodcocks (Scolopax minor) also preferred shrub-
lands and young pine plantations in winter, but could
adapt to a variety of habitats (Krementz and Pendleton,
1994; Krementz and Jackson, 1999).
The compositional analysis showed that mulls humus
soils were preferred to moders and mors. Mulls, slightly
richer in earthworms, constituted the majority of humus
types in wet forests, coppices and plantations. Conifer-
ous timbers ranked fourth in habitat selection, although
they contained few earthworms. Contrary to standard
coniferous forest features, rich patches of earthworms
also existed in the coniferous timbers of the Beffou forest
where one third of soil types were mulls. The presence of
alkaline springs in coniferous stands induced these
patches of mull and hazel trees. Most of the woodcocks
frequenting timbers were in the vicinity of these patches
and avoided mor type humus. The habitat types with
highest earthworms density were also the richest in
shrub cover. Therefore, we conclude that, in winter,
woodcocks choose their habitat in woodlands on the ba-
sis of rich patches of food (e.g., mull humus) and on the
presence of an important shrub strata. However, it is not
possible with our dataset to tease apart the relative
importance of these features that are probably related
to prey accessibility and abundance, and to protection
from predators. Insect larvae biomass and availability
was not considered in this study. Although generally less
abundant in woodland, their occurrence in patches in
some sites that were relatively poor in earthworms might
explain their selection by woodcocks. However, another
study based on the same radio-tagged woodcocks
showed that these birds used different foraging strategies
depending on earthworm availability in their diurnal site
(Duriez et al., 2004). In a site rich in earthworms, they
could stay several day or weeks foraging only by day
and staying in woodlands at night. But in poorer diurnal
sites, they could not meet all their energetic require-
ments without going to fields at night (where there was
always sufficient food). This result suggests that earth-
worm abundance may drive woodcock habitat selection
and behaviour in winter while other invertebrates would
play a secondary role.
Wooded hedges were preferred to shrub or relictual
hedges. Moreover, hedges with a lateral strip were pre-
ferred to hedges without a strip. Because woodcocks
mostly use forests for breeding and wintering, their pref-
erence for the wider and denser hedges, which resembles
a miniature forest habitat, was expected. The shrub and
grass strata, as well as a lateral strip, providing condi-
tions for efficient camouflage, certainly play a role for
protection against predators. Moreover, the presence
of a lateral shrub strip could allow diurnal feeding
opportunities. All the hedges of the study area occur
on embankments. Our protocol to estimate earthworm
biomass was inadequate to sample the hedges, but earth-
worms likely were limited or scarce because of shallow
soil and the current dry soil conditions. In this context,
only the strip, extending the hedge on the field (usually a
meadow), likely provided food in high quantity.
4.2. Nocturnal habitat selection
Meadows (especially old dry grazed meadows) were
preferred by woodcocks over fields of stubble and seed
plots, as found in England and Ireland (Hirons and
Bickford-Smith, 1983; Wilson, 1983; Hoodless, 1994).
Because earthworm biomass (woodcockÕs main prey
item) was four to five times higher in meadows than in
the other cultivated fields, this choice probably reflected
food availability. Binet (1993) found a tenfold reduction
in earthworm biomass when going from a meadow to
corn plot in Brittany. In addition to earthworm abun-
dance, insect larvae was found to be an important com-
ponent of the diet and habitat selection of similar-sized
grassland waders (e.g., Golden plovers Pluvialis apricaria;
486 O. Duriez et al. / Biological Conservation 122 (2005) 479–490
Pearce-Higgins and Yalden, 2003). Although not sys-
tematically measured, insects larvae biomass was con-
siderably lower than earthworm biomass in our study
site. Because its diet is composed of more than 80% of
earthworms in winter (Granval, 1988), we believe that
if woodcock habitat selection is driven by prey availabil-
ity, it should be primarily towards earthworms.
Un-grazed meadows were avoided compared to the
three types of grazed meadows. Grazed meadows sup-
port more earthworms than hay-meadows (Nic¸aise,
1996), because cattle manure serves as food for most
earthworm species (Lee, 1985; James, 1992). Although
we did not sample earthworms in un-grazed meadows,
we did a qualitative visual inspection using a spade
and found numerous earthworms there. In addition to
probable but minor differences in earthworm abun-
dance, we believe that the avoidance of un-grazed mead-
ows is likely the result of the difference in vegetation
structure (tall grass compared to short grass in grazed
meadows). Ferrand and Gossmann (1995) hypothesised
that the short swards of grazed meadows enable easy
mobility of woodcocks and better detection of their
preys and predators. Indeed predation by mammals (feral
cats, foxes and mustelids) mostly happen at night in
fields (Duriez et al., 2005). Such selection of short-sward
grazed meadows were also found in similar-sized grass-
land waders like Lapwings Vanellus vanellus (Mason
and MacDonald, 1999) and Golden plovers (Milsom
et al., 1998; Whittingham et al., 2000; Pearce-Higgins
and Yalden, 2003), and also passerines (Perkins et al.,
2000).
Although grazed meadows were generally preferred,
stubbles ranked second. Stubbles were intensively used
by some individuals (5 birds used them >50% of their
time, and 2 birds >90%). Stubbles probably offered an
easier mobility and prey detection. Moreover, stubbles
following a first cereal crop, after several years in mead-
ows, may be rich in earthworms because of the high in-
put of organic matter in the soil (ploughed-under grass)
(Edwards and Lofty, 1977 in Lee, 1985). In 2000, a first-
year wheat stubble was used every night by 2–3 wood-
cocks. Although the sampling protocol was not applied
in 2000, the presence of hundreds of molehills in this
field indicates that this plot was probably rich in earth-
worms, because Moles (Talpa europaeus) are specialist
predators of earthworms (Granval and Aliaga, 1988).
Fields with molehills, used as an indicator of earthworm
abundance, were also significantly selected by Golden
plovers (Whittingham et al., 2000).
The results of our study suggest that woodcock win-
tering in Brittany use meadow and stubble habitats,
probably in relation to prey availability, which is a com-
bination of sward height and prey abundance. However,
it was not feasible to sample variation in prey abun-
dance and sward height at a sufficiently fine resolution
to tease these components apart. Because of the large
wintering range of the woodcock (from Great-Britain
to the Mediterranean coasts), our study should not be
generalised too widely, although our conclusions on
the influence of the availability of its primary food item
should be fairly robust for such a specialised predator.
Understanding woodcocks wintering strategies will re-
quire additional studies in other parts of the winter
range, in similar environments, as well as in completely
different habitats, for example British moorlands, pine
forests in the French Landes, or Mediterranean
shrublands.
4.3. Implications for conservation management
In winter, woodcock populations use a mosaic of
habitats, including woodlands and fields. Currently,
the few woodcock reserves only prohibit hunting in
woodlands. A more effective reserve would not only lim-
it hunting, but should manage the different habitats
(diurnal and nocturnal) to provide sufficient food and
shelter. The mosaic of habitats (bocage features), once
common, is decreasing and/or changing today.
Although woodlands are now increasing in the Euro-
pean Union, the recent increase of deciduous plantings
follows three decades of massive introduction of conifer-
ous trees in native plain forests. In some parts of their
winter range, woodcocks are found in pine timbers be-
cause it is the only stand type available. Indeed the use
of such habitats by woodcocks seems to be primarily
constrained by the presence of mull soils (synonymous
of high earthworm activity) and dense shrub strata.
Granval and Muys (1992) reviewed that restoration of
degraded forest soils is possible. Some tree species
(e.g., ashes and alders) have an ameliorating effect on
earthworm biomasses (Muys et al., 1992). Moderate lim-
ing without tilling can ameliorate humus if earthworms
are still present (Granval and Muys, 1992). In uninhab-
ited humus (mor), earthworm introduction could be
tried (Huhta, 1979; Brun et al., 1987; Judas et al.,
1997). Because beeches and oaks have relatively acid lit-
ter that favours moder humus formation (Muys et al.,
1992), the plantations in the Beffou forest were limed
with natural mae
¨rl (Fornasier, personal communica-
tion), which probably enhanced earthworm activity
and abundance, resulting in mull type humus.
High earthworms biomass in a diurnal habitat is not
sufficient to attract woodcocks if there is no cover to
protect them. The shrub strata is naturally abundant
in the early stages of plantations but forestry practices
in France tend to suppress it after 20–30 years to man-
age for homogenous stands. The old practice of coppic-
es-with-standard, providing firewood, is often
abandoned. This practice was probably benefiting not
only to woodcocks but also to many other forest species
(mammals and birds) by providing cover and food re-
sources (Fuller and Peterken, 1995). The optimal forest
O. Duriez et al. / Biological Conservation 122 (2005) 479–490 487
habitat for a woodcock is a mosaic of stands of various
ages. Management favouring coppices and mull types
humus (ameliorating trees, liming) should be used. A
simple management technique would be to create
numerous small clearings, allowing the natural develop-
ment of shrub species (hazels, brambles), enhancing
earthworm population growth as well as other
invertebrates.
The conservation of traditional bocage landscapes
with hedges and grazed meadows seems essential for
woodcocks. Agricultural changes are of major concern
for conservation of woodcock in winter and many bird
species in western Europe (Robinson and Sutherland,
2002). Considering the high food potentiality in mead-
ows for woodcocks, the loss of meadows in Europe is
of concern. Moreover, changes in farming techniques
could lead to damages to quality of meadows (Potter,
1997; Wakeham-Dawson and Smith, 2000; Vickery
et al., 2001). Unimproved pastures were preferred to im-
proved pastures by Lapwings and Curlews Numenius
arquata (Barnett et al., 2004). The spreading of manures
and mineral Nitrogen as fertilisers could benefit earth-
worms if done moderately (Cotton and Curry, 1980)
but heavy or high frequencies of applications reduce
invertebrate abundance (Zajonc, 1975; Gerard and
Hayes, 1979; Curry, 1998). In agrosystems dominated
by crops, pesticides also affect earthworms and insect
populations (reviewed in Edwards, 1998), which already
suffer from deep ploughing (Barnes and Ellis, 1979; Ed-
wards, 1983; Binet, 1993). The recent development of
simplified cultural techniques (no-tillage or minimum-
tillage and direct sowing) shows that it is possible to
yield abundant quality crops as under conventional
practices, resulting from auxiliary action of abundant
earthworms (Barnes and Ellis, 1979; House and Parme-
lee, 1985; Baker, 1998). These practices should be
encouraged to protect the soil fauna and their associated
predators. Set-asides, now imposed by the EU Common
Agricultural Policy, are attractive to many bird species
(Henderson and Evans, 2000) and would be attractive
to woodcocks if they are grazed or mowed in autumn,
because earthworm biomasses is higher there than in
crops (Bernard et al., 1998). In agricultural landscape
offering adverse soil conditions (heavy ploughing, low
organic matter content, acid pH), field margins may
serve as refuges for earthworms where they can spread
out into agricultural fields, thereby keeping up high
abundance and biodiversity (Lagerlo
¨f et al., 2002) that
favours their use by birds (Vickery et al., 2002).
Acknowledgements
This study was funded by the Office National de la
Chasse et de la Faune Sauvage. We are very grateful
to all the persons involved in the fieldwork: Y. Chaval,
J.-L. Chil, S. Descamps, C. Guyot, H. Jamin, J. Le Bi-
han, F. Leroy, J. Marie, J.-P. Richard and S. Alary.
G. Eon and V. Farcy determined more than 41,000
earthworms! Many thanks to S. Said, E. Bro, P. Gran-
val, D. Pinaud, H. Lorme
´e, J.-M. Boutin, D.G. Kre-
mentz, D.G. McAuley, J.D. Goss-Custard, C.-A. Bost,
D. Chamberlain and one anonyms refree for useful dis-
cussions and comments on the Manuscript. P. Landry
digitised the map on GIS. We are grateful for the logistic
facilities provided by the Conseil Ge
´ne
´ral des Co
ˆtes
dÕArmor’’, Jean-Claude Fornasier (Office National des
Fore
ˆts). Many thanks to all the farmers for allowing a
free access to their fields.
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