A habitat analysis of badger {Meies meles l.) setts in a semi-natural forest

11 Pages·2001·5.7 MB·English

by  Tatjana C Good

202 D. ASTÜADEMoraes etaL
werden erwogen: 1) Erscheinung der Extrazähne als Folge einer übermäßigen Entwicklung der
Schädelgröße; 2) Atavismus; 3) Persistenz des dritten Milchprämolaren bei Erscheinen des Dauer-
zahnes; 4) Wachstumsstörungen, die zur Verdoppelung eines Zahnkeimes führen. Die erste Hypo-
these wird verworfen, da alle Einzelindividuen eine arttypische Größe haben. Kein fossiler Hinweis
unterstützt auch die zweite. Die Morphologie der beobachteten Zähne unterstützt auch die dritte
nicht, da es sich um Zähne des Dauergebisses handelt. Schließlich ist es schwierig, Beweise gegen
oder zugunsten der vierten Hypothese zu finden, da keine Informationen vorhanden sind, über die
Entwicklung der Zähne bei den bearbeiteten Museumsexemplaren.
References
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Mamm. bioi. 66(2001)204-214 lÄfe Mammalian Biology
© Urban & FischerVerlag i^|M3Bß#
http://www.urbanfischer.de/journals/mammbiol Zeitschriftfür Säugetierkunde
Original investigation
A habitat analysis of badger (Meies meles L.) setts in
a semi-natural forest
ByTatjana C. Good, Karin Hindenlang, S. Imfeld, and B. Nievergelt
Wildlife Research and Conservation Biology, Zoological Institute, University of Zürich, Zürich, Switzerland and
SpatiaLData Handling Division, GeographicalInstitute, UniversityofZürich,Zürich,Switzerland
ReceiptofMs. 27. 07. 2000
AcceptanceofMs. 22. 12. 2000
Abstract
We studied the size, distribution and habitat characteristics of badger (Meies meles L.) setts in a
largely forested area nearthe city ofZürich, Switzerland. The distribution ofthe setts was non-ran-
dom, as revealed by testing nearest neighbour distances. To evaluate the habitat characteristics
that determine sett locations, different parameter categories describing topography, Vegetation
coverand structure ofthe forest habitatwere analysed with a multiple regression analysis and with
a digitalterrain model ofthe forest using a Geographical Information System (GIS). Preferred sett
sites were the convex slopes with an inclination of 20-40°. These sites are well drained and offer
many opportunities for digging entrances and tunnels, and thus gives the badger the Option to
leave the sett from several directions. Ideal sett sites were found above 600 metres a.s.l., closer
to the forest boundary and adjoining agricultural zones than the random points. These sett sites
probably guarantee access to a good food supplyyear-round and allow badgers to adapttheirfora-
ging behaviourto seasonal changes in food availability both within the mixed forestStands and in
the agriculturalfields and meadows outside the forest. Setts were found more than 50 metres from
the nearest path and in areas with sparse ground cover. Coniferous Stands were avoided. However,
Single old spruces within deciduous forest Stands were frequently used as sett sites for setts con-
sisting ofone or two entrances only. Spruce trees have shallow roots, which facilitate digging and
help preventthe roofofthe settfrom collapsing. Vegetation cover played an important role in the
choice ofa sett site. However, just "being out ofview" (be it through topographic characteristics
or distance from the nearest path) could be a type of cover as well. In this study, the small-scale
topography around the setts seemed to play a key role in the choice of sett site. The results pre-
sented here suggestthata large, deciduousforestwith a pronouncedtopographicalVariation repre-
sents a good badger habitat.
Key words: Meies meles, sett distribution, entrance type, sett site, habitat analysis
Introduction
Ingeneral, carnivores not onlyshowgreatin- 1975). The European badger (Meies meles
terspecific diversityin their behavioural ecol- L.) is an example of a species that shows a
ogy (Bekoffet al. 1984; Gittleman 1986) but high degree of plasticity in its behaviour,
also marked intraspecific variability (Wilson adapting its social and spatial Organisation to
1616-5047/01/66/04-204$15.00/0.
A habitatanalysis ofbadger (Meiesmeles L.) setts 205
different environments and food availability. (47°15'N,8°34'E). Itischaracterisedbyadiverse
In high-population-density areas with an mosaic pattern ot mixed deciduous forest domi-
abundant and highly predictable food avail- natedbybeech(Fagussilvatica),withsmallerpro-
ability throughout the year, badgers usually portions of ash (Fraxinus excelsior), other decid-
uous trees, white pine (Abies alba) and the
live in groups, defend small territories and introduced Norway spruce (Picea abies). De-
occupy distinctive main setts (Cheeseman et clared anature reserve in 1994,itCovers approxi-
al. 1981, 1987, 1988; Kruuk 1978; Kruuk mately 1000ha of a forested hill chain, ranging
and Parish 1982, 1987; Nolet and Killing- from470metres a.s.l. at the bottom ofthe valley
ley 1986; Rodriguez et al. 1996; Roper et to over 900metres a.s.l. on the ridge. It belongs
al. 1986; Woodroffe and Macdonald 1992, totheSwissplateauandconsistsofsubalpinemo-
1993). In areas with a seasonally changing, lassic sandstone with partly morrainic cover. The
unpredictable food availability, population dominant soil types contain sandy to silty clay
densities are lower and badgers live in small and argillaceous sand. The extreme relief and
well-drained soils make Sihlwald an ideal place
groups or solitarily, have large overlapping
fordiggingsetts.
home ranges and use several setts within a
ränge (Bock 1986; Cresswell and Harris
1988; Grafet al. 1996;Pigozzi 1989; Skinner
and Skinner 1988). Doncaster and Wood- Methods
roffe (1993) suggested that the spatial Orga-
nisation ofbadgers may be influenced by the TunhteilsAtuudgyusatre1a9w96a.sAseasretcthewdasfordesfeittnsedfraosmaMtalreacsht
distribution of suitable sett sites in a given one entrance leading more than two metres Un-
area. Parameters affecting the distribution of derground, measured with a two-metre flexible
badger setts include the type of soil, the stick. If two entrances were farther than
amount of cover and the hilliness of the ter- 25metres apart, they were considered as two se-
rain (Neal 1986). Most assessments of suita- parate setts. We assumed that practically all setts
ble badger setts have been undertaken in were found. The setts were classified into small
mixed wood- and arable land (e.g. Cress- (1 or2entrances),middle-sized (3 or4entrances)
well et al. 1990). These studies showed an and large (>4 entrances) setts. Five different en-
active selectionforwoodland as sett location. trance typeswere distinguished: entrancesdugdi-
rectly into the ground, under a boulder/rock, un-
However, open fields and meadows were der a spruce (Picea abies), under a deciduous
used as foraging grounds and had an impor- tree and undera stump.
tant effect on sett choice (Hofer 1988; Skin- This study did not differentiate between fox dens
ner et al. 1991). and badger setts for the following reasons.
The goal of this study was to examine sett Although it is known that fox dens usually have
density, sett type and the specific habitat fewer entrances and a different shape and smell
Parametersaffectingthe distributionofsetts thanbadgersetts (Stubbe 1980), the criteriawere
in a highly forested habitat (Sihlwald, Swit- not as clear-cut in Sihlwald with dens/setts con-
sistingofone ortwoentrancesthatwere sporadi-
zerland), offering both ideal digging condi-
cally used by one or both species. Badger hairs
tions as well as good foraging grounds. were found in many setts consisting of one en-
Furthermore, the correlation between the trance only, indicating the presence ofbadgers in
distributionofthe settsincertainparameter single entrance settsaswell.Analysisofsettchar-
categories andthe availability ofthose cate- acteristicsbasedonsettsizerevealednoStatistical
goriesinthe studyareawas explored. difference betweensetts. Therefore, all settswere
included in the habitat analysis presented here.
However,tocomparemainsettdensitywiththose
in the literature, all setts with more than two en-
Material and methods trancesanddefinitebadgersignswere considered
"main setts" (Kruuk 1978). In order to test the
Thestudyarea distributionofthesettsfornon-randomness,near-
est neighbour distances between the setts were
The Sihlwald forest is situated approximately compared with a Monte-Carlo-Simulation of
10km south of the city of Zürich, Switzerland nearest neighbor distances (random distribution,
206 D. TatjanaC. Goodetal.
1000samplesof123points) and thentested using (71.6%), followed by middle-sized (19.5%)
a Chi2-testfortwoindependentsamples. and large (8.9%) setts. Using Kruuk's
The habitat parameters chosen for the analysis (1978) definition of "main setts" (setts with
are summarised in table 1. The parameters were >2 entrances), the density of main setts in
either measured in the field (field data), or ob-
the forest was 3.5/100 ha. The number of
tained from a Geographical Information System
(GIS)usingtheSoftwareArclnfo,whichalsocon- entrancespersettvariedfromone toeleven
tained a digital terrain model ofthe forest based with an average number of 2.3 entrances
on 10metre-contourlines (Tab. 1). The field data per sett. Of the total 279 entrances, 207
were measured within a radius of 25metres of (74.2%) were dug into the ground, while
the approximate centre of the sett. The habitat the rest were dug under some type ofstruc-
analysis was calculated by using a stepwise back- ture (11.1% under spruces, 2.5% under de-
ward logistic regression. The parameters "topo- ciduous trees, 7.9% under boulders, 4.3%
graphy" and "Vegetationunit" were used as cate- under tree stumps).
gorial variables (equivalent to the traditional
group of "dummy variables") (Nievergelt 1981).
The parameters derived from the GIS and the Settspacing
field data could not be analysed together, as the
parameters derived from the GIS were available The average nearest neighbour distance be-
for the whole forest, whereas the field data were tween two setts was 111 metres, compared
available only for the sett sites. For the analysis to 158metres forthe average nearestneigh-
ofthe parameters derived from the GIS, a good- bour distance between two generated ran-
ness-of-fit test compared the numberofobserved dom points. Thus, the observed distribution
setts with the number of expected setts for each of the setts was significantly different from
parameter: area ofthe parameter random (/2-test for two independent sam-
numberofexpectedsetts= area of t-he f.orest ples, p<0.001).
When the nearest neighbour distance was
xtotalnumberofobservedsetts
calculated for the "main setts" only, the
To measure the availability of the habitat para- average nearest neighbour distance was
meters measured in the field (i.e. the parameters 311 metres, compared to the 314metres for
that could not be derived from the GIS database), the average nearest neighbour distance be-
thenumberofsettswascomparedwiththenumber tween two generated random points. The
foofrrtawnodoinmdeppoienntdsenftorsaemapclhesp.arDaumeetteorabsytraon#g2-ctoers-t distribution of "main setts" did not differ
from random.
relationbetween "altitude" and "distance toforest
boundary", the "distance to forest boundary" was
analysed separately. The habitat parameters for
Habitatanalysisofthe setts
whichthe distributionofthesettswasnon-random
were further analysed to see which categories The results of the stepwise backward logis-
(Tab. 1) best explain the sett distribution. Every tic regression showthat sett sites were posi-
parameter category was tested for deviation from tively associated with the parameters "con-
theexpectedvaluebyusinga/2-testinconjunction vex slope", "inclination" and "distance to
withaBonferronizstatistic (Neuet al. 1974). nearestpath" butnegativelyassociatedwith
"concave slopes", "flat areas", "gentle
slopes", as well as "moss-", "herb-" and
Results
"middle layer coverage" (Tab. 2). The re-
sults for the different parameter categories
Settsize and setttype
are as follows:
123 setts were found in the 1000ha study Forest parameters and Vegetation cover:
area of Sihlwald (12.3/100ha). The setts The forest parameters andVegetation cover
were classified according to entrance num- seemed to play a key role. The results
ber (one to two, three to four, more than showed that the parameters ofthe setts dif-
four) and entrance types (five classes, see fered significantly from the availability of
below). Small setts were most common those parameters for "lower layer cover-
A habitatanalysis ofbadger (Meiesmeles L) setts 207
Table 1. Habitatparametersforsetts.Theparameterswereeithermeasuredinthefield (fielddata), orwereob-
tainedfromtheGeographicalInformationSystem (GIS)
Parameter Subscales Categories Sourceofdata
Settlocation X-coordinates continuous Fielddata
Y-coordinates
Altitude metresa.s.l. <600m;<700m;<800m;>800m GIS
Indination degrees 0-10°; 11-20°; 21-30°;31-40°;>40° Fielddata
Aspect degrees N; NE; E;SE;S;SW;W; NW GIS
Topoqraphv* fLat Fielddata
gentleslope
concaveslope
convexslope
crest
Vegetationcover treecover(>1.3 m) Braun-Blanquet(1964): Fielddata
shrubcover(0.5-13m) 0, 1-5%, 6-25%, 26-50%, 51-75%,>75%
herbcover(0-0.5 m)
mosscover
Forestparameters** lower-, middleand Braun-Blanquet(1964): GIS
upperlayercoverage 0, 1-5%, 6-25%, 26-50%, 51-75%,>75%
lower-, middle-and Braun-Blanquet(1964): GIS
upperconiferouslayer 0, 1-5%, 6-25%, 26-50%, 51-75%,>75%
coverage
Vegetationunit GIS
stageofdevelopment 1=younggrowth; GIS
2=polewood;
3=youngtimberwood;
4=middletimberwood;
5=oldtimberwoodI;
6=oldtimberwoodII;
7=oldtimberwoodIII
Distanceto nearest metres <50m;< 100m;<150m;<200m; GIS
path >200m
Distanceto nearest metres <50m;<100m;<150m;>150m GIS
water
Distancetoforest metres <100m;<200m- •<900m;>900m GIS
boundary
* gentle slope: a slanting surface neither curving inward nor outward concave slope: a slope curving inward
convexslope:aslopecurvingoutward, likeasegmentofaglobe.
** datafrom theforestsuperintendent'soffice (WaldamtderStadtZürich), lowerlayercoveragedensity: canopy
densitythatreachesatmost1/3 ofthedominanttree height. middlelayercoveragedensity: canopydensitythat
reaches 1/3-2/3 ofthedominanttree height. upperlayercoveragedensity: canopydensitythatreachesatLeast
2/3ofthedominanttreeheight.
age" and "lower-" and "middle coniferous for herb- and moss coverage (Tab. 3b; y1-
layer coverage" (Tab.3a). However, more test for two independent samples, p<0.05
setts than expected were found only in and p<0.01, respectively), as setts were
areas lacking a "middle coniferous layer more frequently found in areas with little
coverage" (Tab. 4; Bonferroni z statistic, "herb-" and no "moss coverage" (Tab. 4;
p<0.05). The parameters of the setts dif- Bonferroni z statistic, p<0.05 and p<0.01
fered significantly from the random points respectively).
208 D. Tatjana C. Good etal.
Table 2. Habitatparametersthatbestexplaintheoccurrenceofthesetts. Multiplelogisticregression (backward,
stepwise), Model-/=92.36;df= 10; p<0.001; R2=0.77
Habitatparameter B df p-value
Inclination 0.0695 1 0.0006
Topography 4 0.0247
flat -0.6172 0.6818
gentleslope -0.2514 0.8821
concaveslope -1.5706 0.1194
convexslope 0.8271 0.3550
Distanceto nearestpath 0.0144 1 0.0006
Middlelayercoverage -0.0288 1 0.0486
Herb coverage -0.3226 1 0.0351
Mosscoverage -0.8196 1 0.0053
Table3. Comparison ofthe habitat parameters ofthe setts derived from the GIS with the availability ofthose
Parameterswithinthestudyarea (a); comparisonofthe habitatparametersofthesettswiththoseoftherandom
points (b). Onlytheparametersforwhichthedistributionofthesettsissignificantlynon-randomarelisted here.
Goodness-of-fittest; df=degreesoffreedom. For(b): nt=123; n2=85
a) Comparisonwith availability p-value i df
Altitude p<0.001 128.23 3
Aspect p<0.02 16.78 7
Lowerlayercoverage p<0.02 12.69 4
Lowerconiferouslayercoverage p<0.005 12.39 2
Middleconiferous layercoverage p<0.02 10.89 3
Distancetoforestboundary p<0.05 17.61 9
Distanceto nearestpath p<0.001 18.10 3
Distanceto nearestwater p<0.05 10.82 4
b) Comparisonwith random points p-value x2 df
Inclination p<0.001 52.41 4
Topography p<0.001 40.04 4
Herbcoverage p<0.05 19.63 5
Mosscoverage p<0.01 15.44 2
Inclination and topography: Comparison of these three parameters (Tab. 3a). Setts are
the habitat parameters of the setts mea- found significantly closer (<100m) to the
sured in the field with those of the random forest boundary than expected (Tab. 4;
points (Tab. 3b) showed that setts differed Bonferroni z statistic, p<0.05). Signifi-
significantly from random points for "incli- cantly more setts than expected were found
nation" and "topography" (both: /2-test for >50m but <100metres to the nearest road
two independent samples, p<0.001). "Con- or trail (Tab. 4; Bonferroni z statistic,
vex slopes" with the inclination categories p<0.001). No difference was obtained for
<30° and <40° were significantly preferred any category of the parameter "distance to
sett sites (Tab. 4; Bonferroni z statistic, nearest water". Altitude and aspect: The
p<0.001). distribution of the setts was non-random
Distances to forest boundary, forest roads for "altitude" (Tab. 3a;x2-test f°r two inde-
and trails, and water: The distribution of pendent samples, p<0.001) as well as for
the setts was decidedly non-random for "aspect" (p<0.02). More setts were found
—
i. 1 1
A habitatanalysis ofbadger (Meiesmetes L) setts 209
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Fig. 1. Parameters posi-
tivelyaffecting settsitein
soil:eutriccambisol,\ SihLwaLd. Grey ovals: Para-
dosedistancetofood gleyiccambisol ~M meters measured in this
study or taken from avail-
outsidetheforest
able data sets for the
study area. White ovals:
/geoiogy: molassicsandstone
{^singlespruces V^with partlymorrainiccover^ Parameters that are diffi-
cultto assess butprobably
influence the choice of
/lowherb-andmosscoverage sett sites. Arrows indicate
Vjowconiferouslayercoverage^ the interrelations between
the parameters.
>600metres a.s.l. (Tab. 4; Bonferroni z sta- data). We suggest that badgers living in
tistic, p<0.001). No significant difference Sihlwald can optimise their foraging effi-
was obtained for any category of "aspect" ciency by using different setts within their
otherthanNorth, forwhichfewersetts than home ränge according to the proximity of
expected were found (Tab. 4; Bonferroni z the seasonally most profitable food patches.
statistic, p <0.05). Figure 1 illustrates the Future analysis of the seasonal sett-use to-
different parameters positively affecting gether with seasonal variations in foraging
sett sites in Sihlwald. behavior in the study area will provide the
necessary data to test this hypothesis.
In Sihlwald, 28.4% of the setts found
Discussion showed more than two entrances and could
indicate main setts (Kruuk 1978). How-
ever, their distribution did not differ from
Settsize and setttype
random and therefore did not show a spa-
The number of entrances per sett in Sihl- cing-out mechanism indicating territories
wald, ranging from one to eleven. was well according to the fixed-territory model pro-
below the average found in the literature posed by Doncaster and Woodroffe
(1 to 21: Kruuk 1978; 1 to 38: Anrys and (1993) for a high-density badger popula-
Libois 1983; 1-80: Roper 1992a. b), even tion.
compared to that of the other studies in With regard to the entrance types, it is sur-
Switzerland (1-28: Graf et al. 1996: 1 to prising that 31 entrances (11%) were dug
15: Ferrari 1997; 2-23: Monnier. unpub- under relatively large spruces. Although
lished data: 1-34: DoLinhSan, unpublished sett locations have been analysed in several
data). Badgers seem to prefer burrowing studies, only Bock (1986) classified differ-
more setts but with fewer entrances in the ent sett types. However, his study did not
forest than in the agriculture zone where mention anything about setts dug under
sett sites are restricted to the little patches spruces. The spruces in Sihlwald were all in
of forest between the agricultural fields mixedforests. Apossible explanationis that
and meadows (DoLinhSan, unpublished spruce trees are normally shallow rooted
A habitatanalysis ofbadger (Meiesmeles L) setts 211
(Köstler et al. 1968; Blanckmeister and have several advantages. The badger can
Hengst 1971), compared to the dominant pick up scents from different directions
beech trees in Sihlwald. Shallow roots facil- without having to leave the security of the
itate digging; also the roots keep the roofof sett and thus have several directions from
the sett from collapsing. It is also ofinterest which to leave a sett. It is also possible that
to note that 22 entrances (7.9%) were dug setts on convex slopes are easier to enlarge
under a boulder/rock. To our knowledge, because the rounded shape of the slope
single rocks as a possible habitat parameter gives the badgers more opportunities for
for sett location, providing shelter and good digging entrances and connecting tunnels
thermal insulationhas onlybeen mentioned than an unstructured slope. Inclination
in one other study (Virgos and Casanovas ("hilliness" according to Thornton 1988) is
1999). also closely associated with topography.
Setts are usually dug in slopes (Neal 1986;
Skinner et al. 1991). The hilliness of the
Coveras keyfactor
study area is advantageous to the badger in
The habitat parameters affecting the distri- various ways. Digging in a slope facilitates
bution of setts in Sihlwald correspond clo- the removal of the excavated soil, which
sely to those identified by Neal (1986) and Spills down the slope. A particularly favour-
Thornton (1988): digability, hilliness and able Stratum of soil for digging is more ea-
(tree-) cover. Cover allows the badgers to sily found on a slope since it is more likely
leave inconspicuously, and it allows the to be exposed. Sloping land is usually well
young cubs to play near the entrance with- drained so that the sett is more likely to be
out being visible to potential predators. A warm and dry, and in colder parts a depth
closer look at the Vegetation cover around below ground is quickly attained which is
the preferred sett sites in Sihlwald shows frost free (Neal 1986).
that these sites are areas of sparse ground
cover (i.e. low herb- and moss coverage).
Settdensityand population density
High herb and moss coverage often is cor-
related with humidity and therefore The density or setts in Sihlwald (12.3/
avoided by badgers as sett sites. As ob- 100ha) is very high compared to the den-
served in other studies (Neal 1986; Zejda sity of the nearby agricultural zone (2.7/
and Nesvadbova 1983), coniferous Stands 100ha, DoLinhSan, unpublished data).
providing little Vegetation cover and found This implies that suitable sett sites are not
in rather flat areas were avoided in Sihl- a limiting factor in the forest, as suggested
wald. The preference forconvexslopeswith by Roper (1993) for British areas. Otherre-
a high inclination (20-40°) as well as the gions of Switzerland (Canton of Neuchätel:
preference for a minimum distance of 50m 0.02-0.2/100ha, Monnier, unpublished
from the next path suggest that the variable data; Canton of Berne: 4.2/100ha, Graf et
"cover" is not necessarily equivalent to Ve- al. 1996) have also lower sett densities. Still,
getation cover; the small-scaled topography Sihlwald has a significantly lower sett den-
around the sett and the distance to the sity than found in Britain (up to 26/100ha,
nearest path (just "being out of view") can Cresswell et al. 1990). The density ofpos-
indirectly be a type of cover as well. Topo- sible main setts in Sihlwald (3.5/100ha) is
graphy, i.e., the physical shape of the area comparable to that in the high-badger-den-
in which a sett is dug, is a parameter that sity areas in Britain (Clements et al. 1988,
has never been stressed in the literature see Kowalczyk et al. 2000, for review).
before and seems to play a key role in the Based on the available earthworm biomass,
choice of sett site in Sihlwald. Paying at- which is the most important food source
tention to the small-scale topography forbadgersinSihlwald, theminimumpopu-
(050metres) around the sett appears to lation size is estimated to be 2.5 to 3 indivi-
be important. Setts dug in convex slopes duals per 100ha (Hindenlang, unpub-