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Tamara KIRIN, Jelena KRALJ, Davor ĆIKOVIĆ, Zdravko DOLENEC

ABSREACT: The effect of floristic and structural characteristics of vegetation
on the forest songbird communities in two Nature Parks: Medvednica andŽumberak – Samoborsko gorje was studied. The point-count method was used
for analyzing songbird communities and circular plot method for habitat mapping,
on 101 points at both sites. Non-parametric test were used (Kruskal–
Wallis and Kendal Tau). The tree basal area was used to classify studied
points into five forest types (beech, oak, mixed deciduous, coniferous and
mixed coniferous forests) and as indication of the stand maturity. The total of27 and 32 songbird species were recorded on Medvednica and Žumberak –
Samoborsko gorje respectively. Diversity was higher on Žumberak – Samoborsko
gorje due to greater habitat fragmentation, while population density of
songbirds was greater on Medvednica. Among structural characteristics,
those related to forest age (average tree basal area and number of the small
trees) had the most pronounced effect to the total songbird density and densities
of different ecological groups of birds. Sorensen index showed that in spite
of the differences in floristic composition between particular forest types in
two studied areas (0.475 ± 0.120), songbird communities showed high similarity
(0.872 ± 0.070). The highest similarity of songbird communities between
Parks was recorded in beech and oak stands. Oak stands showed the lowest similarity
in tree species composition and no significant difference in structural
characteristics, while beech stands had many different structural features and
several differences in densities of ecological groups of birds. The greatest difference
of bird densities in the particular forest type between two Parks was
found in beech and mixed coniferous stands. High structural differences between
these two forests were the result of the forest age; bird populations had
higher densities in older stands.

Key words:songbird communities, forest habitat, vegetation structure,
Nature Parks


Habitat choice in birds is affected by two groups ofcompetition (Pielou1978). Birds have greater potenfactors:
species requirementsand inter- and intraspecifictial for habitat selection than other taxonomic groups,


due to their extreme mobility and diversity of ranges.

Tamara Kirin, dipl. ing., Dipartimento di tecnologie, ingegneria e
scienze dell’Ambiente e delle Foreste (D.A.F.), Universita degli
Great seasonal changes in forest habitats force forest
Studi dellaTuscia, 01100 Viterbo, Italy,

birds, especially migratory insectivores, to re-establish


their residence annually and quickly in appropriate habi


Dr. sc. Jelena Kralj, dr. sc. Davor Ćiković – Institute of Ornithology,
Croatian Academy of Sciences andArts, Gundulićeva 24,
tats.This has probably resulted in strong selective pres-
Zagreb, Croatia, e-mail:

sures on their patterns on habitat choice (Cody1985,


Prof. dr. sc. Zdravko Dolenec, Department of Zoology, Faculty of


Science, University of Zagreb, Rooseveltov trg 6, Zagreb, Croatia

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T. Kirin, J. Kralj, D. Ćiković, Z. Dolenec: HABITAT SELECTIONAND SIMILARITYOF THE FOREST ...Šumarski list br. 9–10, CXXXV (2011), 467-475
Abundance of forest birds is largelydependent on the
forest types. Studies which relates habitat characteristics
to species abundance often has a goal to find out
whether structural or floristic characteristics of vegetation
has more impact to species distribution abundance.
While MacArthurand MacArthur(1961) and
Blondeletal. (1973) consideredthatphysiognomic
structure of foresthasmajorimpact on small insectivorous
forest birds, Moskát(1988) foundthat floristic
structureis the most important factor affecting bird population
densities.These studies do not explain why birds
occupy particulate habitats, but they identify habitat
characteristics which appear regularly in bird territories
and which may be correlated with proximate factors in
habitat selection (Bertin1977). Bird-habitat correlations
are just one segment of the analysis of habitat selection
(Sherryand Holmes1985). Although they

do not give information about the processes or dynamics
of habitat selection, they have a value as a tool in the forest
management. Forest bird communities are, unlike
many plants and invertebrates, relatively little affected
by historical factors (Fuller1990) and changes in forest
management practice can quickly affect breeding
bird communities.

In this study, we compared bird communities and
floristic and structural characteristics of forests in two
Nature Parks in northwest Croatia. Our aim was to
identify the most important habitat characteristics that
influence the diversity of songbird communities and
density of ecological group of birds in different forest
stands.We also test whether higher similarity of physiognomic
or floristic structure results with higher similarity
of bird communities between two studied areas.

Study area covers the territory of
two Nature Parks, Medvednica
(45°51’N 15°51’E– 46°01’N 16°12’
E) and Žumberak – Samoborsko
gorje(45°43’N 15°15’E– 45°47’N
15°41’E) situated in NW Croatia,
only 15 km apart (Fig1), on altitudes
from 100 to 1178 meters above sea
level. Climatic and geological characteristics
and vegetation cover of
the two mountains are similar. Both
mountains are part of Croatian continental
karst.Average annual temperature
is around 6oC and annual
precipitation around 1200 mm with
the rain maximum from April to
September. Forests cover over 60%
of area in both Nature Parks, but
they are mostly continuous on
Medvednica and more fragmented
on Žumberak – Samoborsko gorje.
Forests of sessile oak and common
hornbeam Epimedio-Carpinetum
betu li(Ht. 1938) Borhidi1963 are
predominant in the lower mountain
area, forests of sessile oak and chestnut
Querco petraeae-Castanetum
sa tivaeHt. 1938 grow on more acid
soils,while forests of pubescent oak

METHODS – Metode

Study Area –Područje istraživanja

Figure 1Position of the study area.

Slika 1.Položaj istraživanih područja.

and hop hornbeamOstryo-Quercetum pubescentis, (Ht.AbietetumVukelićet Baričević2007, while on
1950) Trinajstić1979cover steeper and warmerŽumberak– Samoborsko gorje fir-beech forests are not
slopes.The beech forestsAremonio-Fagion(Horvatpresent (Trinajstić2001) and coniferoustrees (fir
1938) Borhidi in Töröketal. 1989 and Luzulo-Fa-Abies albaMill., sprucePicea abies(L.) Karsten, pine
gionLohm et R.Tx. in R.Tx. 1954predominate in thePinus sylvestrisL. and larchLarix deciduaMill.) are
higher mountain area.The highest parts of Medvednicaonly cultivated(Jelaskaet al2005, Nikolićand
are covered with fir-beech forests Festuco drymeiae-Kovačić2008).

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T. Kirin, J. Kralj, D. Ćiković, Z. Dolenec: HABITAT SELECTIONAND SIMILARITY OF THE FOREST ...Šumarski list br. 9–10, CXXXV (2011), 467-475
Bird Community Sampling –Metode istraživanja ornitofaune

The study was carried out during breed ing seasons
2006 and 2007. Standard point count method was used
(Bibby et al. 1992),with 10 minutes counting period.
Two counting bands were used:inner – with the diameter
of 50 m and outerclose to the infinity.The research
wascarriedon49 points on Medvednica and 52 on
Žumberak – Samoborsko gorje. Counting points were
situated inside the forest, at least 500 m apart. Every
point was visited three times during the breeding season:
inApril, May and June.Visits started after the sunrise
and lasted up to three hours, covering the period of
the highest bird activity. Singing males were con sidered
as representing breeding territories. For quantitative
analysis, only birds recorded in the inner band
wereused. Songbird species with largebreedingterri

tories (as Jay – Garrulus glandariusand Raven–
Corvus corax) were excluded from the analyses.

For detailedanalyses of bird communities, species
were grouped according to their breeding and foraging
ecology. Regarding the nest site, birds were divided
into four groups: i) canopy nesting species,ii) species
nesting in the shrub layer, iii) hole-nesting species and
iv) ground nesting species. Regarding the layer where
birds feed they were divided into five groups: i) canopy
feeding species, ii) species feeding in shrub layer, iii)
bark gleaning species, iv) ground feeding species and
v) aerial feeders (Table 1). Species recorded with only
one specimen during the study were excluded from
analyses of ecological groups.

Habitat Sampling –Metode istraživanja staništa

At each counting point, habitat mapping was carried
out by the circular plot method (JamesandShugart
1970, Cyrand Oelke1976,Bibbyetal. 1992).
Plot size was 0.04 ha.The tree species and tree diameter
(DBH) were recorded for each tree inside the plot.
Tree diameter was measured with the calibrated ruler
and is given in eight classes:A7.5–15 cm, B 15–23 cm,
C 23–38 cm, D 38–53 cm, E 53–68 cm, F 68–84 cm,
G 84–101 cm, H > 101 cm.Tree height was not measured.
Basal area was calcu lated for trees in each diameter
class, accord ing to Cyrand Oelke(1976). The
average tree basal area was calculated by dividing the
total basal area with the total number of trees on the plot
and was used as indication of the stand maturity (Bibby
et al. 1992). For further analyses, trees from groupAand
B were pooled together as “small trees”, C, D and E – as
“medium sized trees” and F, G and H – as “large trees”.

The shrub density was recorded along two transects
of outstretched armlength across the circular plot, each
equals to approximately 0.008 ha.The percentages of
ground cover and cano py cover were calculated basing
on 20 readings made through a sighting tube with cross

Data Analyses–

Shannon-Weiner (H’) index was used for calculating
diversity of communities (Odum1971).Sorensen
index was used for comparison of similarity in structural
characteristics of forests and bird communities
between two study areascommunities (Odum1971).

Shapiro-Willks Wtest showed that variables were
not normally distributed. Therefore, non-parametric

threads taped across one end of a tube. Detailed floris

tic structure of the shrub and ground layers was not

studied, only the dominant species were noted.

We didn’t attempt to determine the forest community
for every counting point. Instead, the proportion of tree
basal area per species was used to classify studied points
into five forest types (Delahayeand Vandevyvre
2008) (beech, oak, coniferous, mixed deciduous and
mixed coniferous forests). Counting points with more
than 70% of total basal area belonging to the beech
(Fagus sylvaticaL.) and those with more than 50 % belonging
to the oak (Quercussp.) were classified as beech
and oak stands, respectively. If more than 70% of total
basal area referred to coniferous trees of any species (fir,
spruce, pine and larch),counting point was classified as
coniferous stand. Other points were classified as mixed
stands, either deciduous or coniferous, depending on
presence of coniferous trees. Habitat sampling methods
and classification of forest types differ from standarised
methodology used in forestry. Applied methods thus
were not comparable with methods used in systematic
forest inventory in Croatia.

Analiza podataka

tests (Chi-square, Kruskal–Wallis and Kendal Tau)
were applied.All statistical analyses were performed
using Ecological Methodology (Krebs2003) and
STATISTICA v.7.0(StatSoft 2004) software.

RESULTS – Rezultati
During this study, 27 songbird species weretypes, except in the beech stands, were higher in
recorded in the forests of Medvednica and32in Žum-Medvednica. Contrary, Shannon – Wiener index of diberak
– Samoborsko gorje, with27species present inversity of bird communities in almost all forest types
both Parks (Table 1). Densities of birds in all forestwas higher in Žumberak – Samoborsko gorje (Fig 2).

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Ecological groups of songbirds regarding their breeding and foraging niche and densities in different forest types. A presence of species recorded only in the outerband is showed with a sign *. Nest site:c –canopy nesting species,s–species nesting in the shrub layer, h–hole-nesting species, g –ground nesting species. Foraging
site: c –canopy feeding species, s –species feeding in shrub layer, b –bark gleaning species, g –ground feeding species anda –aerial feeders.The number of studypoints per forest type is given in the parenthesis.

Tablica 1.Ekološke skupine ptica pjevica obzirom na mjesto gniježđenja i hranjenja te gustoća populacije u različitim tipovima šuma. Prisutnost vrsta zabilježenih samo uvanjskom pojasu prikazana je znakom *. Prema mjestu gniježđenja; c – gnjezdarice krošnji, s – gnjezdarice grmlja, h –dupljašice, g – gnjezdarice na tlu. Prema mjestu
hranjenja: c – vrste koje se hrane u krošnji, s – vrste koje se hrane u grmlju, b – vrste koje se hrane na deblu, g – vrste koje se hrane na tlu i a – vrste koje hranuhvataju u zraku. Broj točaka na kojima je izvršeno istraživanje naveden je u zagradama za svaki tip šume.

Ecological group/ekološka grupa
Density (pairs/km2
) /gustoća (parova/km2)
Medvednica (N=49)Žumberak-Samoborsko gorje (N=52)
Tree Pipit/prugasta trepteljka(Anthus trivialis) gg
Wren/palčić(Troglodytes troglodytes)gg
Robin/crvendać(Erithacus rubecula)gg
Blackbird /kos(Turdus merula)sg
Song Thrush/drozd cikelj(Turdus philomelos)sg
Mistle Thrush/drozd imelaš(Turdus viscivorus)cg
Garden Warbler /siva grmuša(Sylvia borin)--
Blackcap /crnokapa grmuša(Sylvia atricapilla)ss
Wood Warbler/šumski zviždak(Phylloscopus sibilatrix)--
Chiffchaff / zviždak(Phylloscopus collybitus)gc
Goldcrest /zlatoglavi kraljić(Regulus regulus)cc
Firecrest /vatroglavi kraljić(Regulus ignicapilla)cc
Collared Flycatcher /bjelovrata muharica(Ficedula albicollis)ha
Red-breasted Flycatcher /mala muharica(Ficedula parva)--
Long-tailed Tit /dugorepa sjenica(Aegithalos caudatus)sc
Marsh Tit /crnoglava sjenica(Poecile palustris)hc
Willow Tit/planinska sjenica(Poecile montanus)hc
Coal Tit /jelova sjenica(Periparus ater)hc
Blue Tit /plavetna sjenica(Cyanistes caeruleus)hc
Great Tit /velika sjenica(Parus major)hc
Nuthatch /brgljez(Sitta europaea)hb
Treecreeper/kratkokljuni puzavac(Certhia familiaris)hb
Short-toed Treecreeper /dugokljuni puzavac(Certhia brachydactyla)hb
Red-backed Shrike /rusi svračak(Lanius collurio)--
Golden Oriole /vuga(Oriolus oriolus)cc
Starling /čvorak(Sturnus vulgaris)hg
Chaffinch / zeba(Fringilla coelebs)cg
Greenfinch /zelendur(Carduelis chloris)--
Common Crossbill /krstokljun(Loxia curvirostra)--
Bullfinch/zimovka(Pyrrhula pyrrhula)--
Hawfinch /batokljun(Coccothraustes coccothraustes)cc
Yellowhammer / žuta strnadica(Emberiza citrinella)--
Total density/ukupna gustoća

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The highest bird population densities were found inspecies in particular forest type between two study areas

oak and mixed coniferousstands.
Fourthe most abundant species (that include
ChaffinchFringilla coelebsandRobinErithacus rubeculain
all forest types, and eight other species depending
on the forest type) made 45–53 % of songbird population
in Medvednica and 41–50 % in Žumberak – Sa mo borsko
gorje. They had the lowest percentage in oak
stands and the highest in mixed stands.The differences
between the proportion of four the most abundant


were not significant (.test).Six bird species showed
the preference for the particular forest type (with more
than 40% of pairs recorded in one forest type).Those
were Willow Tit (Poecile montanus), Firecrest (Regulus
ignicapilla) and Eurasian Treecreeper (Certhia familiaris)
in mixed deciduous stands, Goldcrest (Regulus
regulus) and Coal Tit (Periparus ater) in coniferous
stands and Short-toed Treecreeper (Certhia brachydactyla)
in oak stands. The association between the

Figure 2
Average population densities (bars) and Shannon-Wiener biodiversity index (lines) of bird communities in
forest types of two studied areas.

Slika 2.Gustoće populacija (stupci) i Shannon – Wienerov indeks raznolikosti (linije) zajednica ptica u različitim
tipovima šuma na dva istraživana područja.

Figure 3Sorensen index of similarity of tree species and bird species composition of particular type of forest between two studied areas.

Slika 3.Sorensenov index sličnosti vrsta drveća i ptica u pojedinom tipu šuma između dva istraživana područja.

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Goldcrest and coniferous forests was very strong: Gold-that studied beech standswere older on Žumberak,
crest was one of the four the most abundant species inwhile other forest stands were older in Medvednica.
that forest type.Forests in Medvednica generally had higher shrub
layer density (Table 2). Significant differences among

Similarity of songbird communities of particular
ecological groups of birds breeding in particular forest

forest types between two study areas was high(0.872 ±
types was found only in beech, mixed deciduous and

0.070),while floristic similarity of tree species was relmixed
coniferous stands, for ground and hole nesters

atively low(0.475 ± 0.120) (Fig 3). Contrary to florisand
birds feeding on the ground, on the bark and in the

tic structure, structural characteristics of forests
scrub layer (Table3).Densities of almost all ecological

showed much higher differences between two study
groups were higher on Medvednica, with the exception

areas. Only oak stands didn’t show any significant difof
those in beech stands.

ference in measured structural characteristics.The average
tree basal area and ratio of small trees showed

Table 2
Structural differences of forest types between two studied areas. Differences were tested by Kruskal – Walllis test.

p:* < 0.05, **< 0.01, ***< 0.005.There were no significant differences for any structural characteristic in the
oak stands.
Tablica 2.Razlike u strukturi pojedinih tipova šuma između dva istraživana područja. Razlike su testirane Kruskal – Wallisovim
testom. p: * < 0.05, **< 0.01, ***< 0.005. U hrastovim sastojinama nije bilo statistički značajnih razlika
između istraživanih područja.

Beech stands
Coniferous stands
Mixed deciduous
listopadne sastojine
Mixed coniferous
stands (N=12)
crnogorične sastojine
Number of trees/ha
/broj stabala/ha6784668.444***48810717.097**9059680.92937214257.385**
Scrub density (stems /ha)
/gustoća grmlja (stabljika/ha)4883.31244.88.796***1750.0928.61.310835.93227.36.502**1531.31218.80.117
Ground cover (%)
/pokrovnost tla (%)45293.33561194.422*36380.13859256.173**
Tree cover (%)
/pokrovnost (sklop)krošnji(%)86943.953*65823.04583914.768*78913.684
Ratio of small trees (%)
/udio tankih stabala (%)66478.613***41695.166*66751.65037736.490**
Average tree basal area (m
/prosječna temeljnica(m2/ha)0.0630.0996.601**0.1100.0415.143*0.0500.0363.3340.1400.0387.385*


Table 3
Differences among densities (in pairs/km) of ecological group of birds between two study areas. Differences were
tested by Kruskal –Wallis test. p: * < 0.05, **< 0.01.

Tablica 3.Razlike u gustoćama (parovi/km2) pojedinih ekoloških grupa ptica između istraživanih područja. Razlike su testirane
Kruskal – Wallisovim testom. p: * < 0.05, **< 0.01.

Beech stands
Mixed deciduous
stands (N=27)
listopadne sastojine
Mixed coniferous
stands (N=12)
crnogorične sastojine
ground nesters/gnjezdarice tla3.313.340.0152.553.595.161 *4.142.556.417 **
hole nesters/dupljašice2.724.777.425 **5.252.894.535 *
feeding on the ground/hranjenje na tlu4.926.534.225 *7.405.903.3928.446.054.071 *
feeding in scrub layer/hranjenje u grmlju1.360.854.446 **1.111.390.6141.591.271.100
bark gleaning/hranjenje na deblu0.511.062.3221.510.584.213 *1.430.003.618

The total songbird density was positively correlated
with the average tree basal area (Table 4). Hole nesters
and bark gleaning species preferred the same forest
characteristics and both had the densest populations in
oak stands.They were both negatively correlated with
the number of small trees and number of trees on the
plot and positively correlated with average tree basal

area. Canopy-feeders showed positive and ground-feeders
negative correlation with shrub layer density. Birds
nesting in the canopy showed positive correlation with
the number of the large trees, and average tree basal area
and had the highest density of population in mixed
coniferous stands.

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SAŽETAK: Istraživanja zajednica ptica pjevica šumskih staništa ukazuju
da na njihovu strukturu i gustoću populacija mogu utjecati floristička i strukturalna
svojstva vegetacije. U ovom istraživanju željeli smo, usporedbom zajednica
ptica šumskih staništa dvaju parkova prirode, utvrditi utjecaj
florističkih i strukturalnih svojstava vegetacije na zajednicu ptica gnjezdarica.
Istraživanje je provedeno tijekom 2006. i 2007. u Parkovima prirode Medvednica
i Žumberak – Samoborsko gorje. Šume pokrivaju oko 60 % površineu oba parka, ali su kontinuirane na Medvednici i nešto rascjepkanije na Žumberku.
Istraživanje ptica provedeno je metodom prebrojavanja u točki, a uzorkovanje
staništa metodom kružnih ploha. Istraživanje je provedeno na ukupno101 točki: 49 na Medvednici i 52 na Žumberku. Pri statističkoj obradi korišteni
su neparametrijski testovi (Kruskal–Wallis i Kendal Tau). Udio temeljnice
stabala korišten je za određivanje pripadnosti pojedinom šumskim tipu:
bukovoj, hrastovoj, mješovitoj listopadnoj i mješovitoj crnogoričnoj šumi.
Prosječna temeljnica stabla korištena je kao indikator starosti šume. Istraživanjem
je zabilježeno ukupno 27 vrsta ptica pjevica u šumama Medvednice i32 na Žumberku (Tablica 1). Šest vrsta ptica bilo je vezano uz određeni tip
šume, s više od 40 % parova zabilježenih u tom šumskom tipu. Diverzitet vrstabio je viši na Žumberku, dok je gustoća populacija ptica pjevica bila veća na
Medvednici (Slika 2). Sorensenov indeks pokazao je da zajednice ptica istog
tipa šume između dva područja pokazuju znatno veću sličnost nego floristički
sastav (Slika 3). Najveća sličnost u zajednicama ptica između dva Parka zabilježena
je u bukovim i hrastovim sastojinama. Hrastove sastojine pokazuju
najmanju florističku sličnost, ali nemaju značajnih razlika u strukturalnim
svojstvima niti u ekološkim skupinama ptica. Bukove sastojine naprotiv pokazuju
značajne strukturalne razlike i u njima je, kao i u mješovitim crnogoričnim
sastojinama, zabilježena najveća razlika među ekološkim skupinama
ptica između dva Parka. Strukturalne razlike tih šuma između dva Parka su
rezultat različite starosti sastojina, a ptice su imale veće gustoće u starijim šu-
mama. Među strukturalnim svojstvima vegetacije, ona vezana uz starost šume
(prosječna temeljnica i broj mladih stabala) bile su značajno korelirane s
ukupnom gustoćom populacija pjevica i s gustoćom različitih ekoloških skupina.
Zaključak je ovog istraživanja da floristički sastav šuma ima utjecaj na
odabir tipa šume u kojoj će se neke vrste ptica pjevica gnijezditi, dok na odabir
samog područja gniježđenja veći utjecaj imaju strukturalna svojstva šume.

Ključne riječi:zajednice ptica pjevica, šumska staništa, struktura vegetacije,
Parkovi prirode

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Table 4
KendallTau correlation between several ecological groups of songbirds and structural characteristics habitat in
study area. Significant values are given in bold.

Tablica 4.Kendall Tau korelacija između nekih ekoloških skupina ptica i strukturalnih svojstava vegetacije na istrživanom
području. Značajne korelacije označene su masno.

total hole barkcanopy canopy ground
songbird /nesters /gleaning /nesters /feeder /feeder /
pjevicedupljašicehranjenje gniježđenje hranjenje hranjenje
ukupnona debluu krošnjiu krošnjina tlu
Number of trees/ha – -0.097-0.150-0.159-0.094-0.049-0.077
broj stabala/hap=0.14p<0.05p<0.05p=0.16p=0.46p=0.24
Average tree basal area (m/ha) –0.1500.1910.1930.1410,0400.129
prosječna temeljnica (m2/ha)p<0.05p<0.005p<0.005p<0.05p=0.54p=0.05
Number of large trees/ha –0.1260.1160.0920.1430.0840.118
broj velikih stabala/ha–p=0.06p=0.08p=0.16p<0.05p=0.21p=0.08
Number of small trees/ha –-0.122-0.168-0.160-0.119-0.029-0.109
broj malihstabala/hap=0.06p<0.05p<0.05p=0.07p=0.66p=0.10
Scrub density (stems /ha)–-0.084-0.020-0.040-0.1570.168-0.30
gustoća grmlja (stabljika/ha)p=0.21p=0.76p=0.55p<0.05p<0.05p<0.001


Two Nature parks, Medvednica and Žumberak –
Samoborsko gorje are situated in the same region and
are covered with similar forest types. Main differences
are less continuousforest cover and lack of natural
coniferous forest on Žumberak – Samoborsko gorje.
Higher number and diversity of songbird species on
Žumberak – Samoborsko gorje might be a result of
greaterhabitat fragmentation on that mountain (Jelaska
et al. 2005).This might alsobe a reason why several
edge species were recorded in the study (as
Red-backed Shrike andYellowhammer). Habitat fragmentation
can cause higher diversity of birds species
and also the increase of population density (Odum
1971), but in our study population densities were
higher in Medvednica.The reason is the fact that we
studied only birds of forest interior. Continuous forests
on Medvednica and older age of forest represent better
habitat for forest interior species.

In regards to the floristic structure of tree layer, similarity
between these two areas is relatively low. It is
the result of the low proportion of the silver fir in Žumberak
– Samoborsko gorje that is replaced by the
spruce and other cultivated species (Trinajstić
2001). Oak stands covered with this study dominated
with theSessile OakQuercus petraea on Medvednica
and with Turkey Oak Quercus cerrison Žumberak –
Samoborsko gorje.

Number of birds was restricted to particular forest
type.These are species dependent on coniferous trees
(as some tits, Goldcrest and Firecrest) or oak trees
(Short-toed Treecreeper). On larger spatial scale, the
floristic composition has an important effect to song

bird communities, determining the presence or absence

of particular species. The most abundant birds in all

forest types were Chaffinch and Robin, the commonest

bird species in almost all types of European forests and
therefore considered as forest generalists (Moskát

In spite of relatively low similarity of floristic structure,
similarity of bird communities between two studied
areas was very high.The highest similarity of bird
communities was recorded in beech and oak stands.
Oak stands showed the lowest floristic similarity, but
no significant differences in any structural variable of
habitatand no significant differences in the density of
any ecological group of birds. On the contrary, beech
standshad medium floristic similarity (0.64), many different
structural features(number of trees, shrub density,
the ratio of small trees and the average basal area)
and several differences in densities of ecological
groups.Therefore, it can be concluded that quantitative
structure of bird communities was more dependent on
structural characteristicsof habitat than on floristic
structure of forest stands.

The highest densities of birds were found in oak and
mixed coniferous stands in Medvednica. Oak forests
are generally characterized with a vertical complexity
resulting with the high number of ecological niches
(Moss1978),while mixed coniferous stands of
Medvednica had high ratio of large trees (20%)indicating
older age.The assumption that in managed forest
the limitation factor for bird density could be number of
old trees (Berg1997) was confirmed by our research
as the same forest type in Žumberak – Samoborsko
gorjehas the lowest species richness and is the only
stand with no large trees and 73% of small trees.

Bark gleaning species showed the preference for
the old forest and highest densities in oak stands


(1.49 – 1.94 pairs/km) which both can be explained
with number of the insects on the bark. Number of in

ŠUMARSKI LIST 9-10/2011 str. 60     <-- 60 -->        PDF

T. Kirin, J. Kralj, D. Ćiković, Z. Dolenec: HABITAT SELECTIONAND SIMILARITYOF THE FOREST ...Šumarski list br. 9–10, CXXXV (2011), 467-475
sects is greater on older trees and significantly greater
on the oak trees in comparisons to other tree species
(Southwood1961). Species feeding in canopy were
positively correlated with quantity of shrub proving that
their feeding area is equally canopy and higher shrub
layer. Species feeding on ground avoided foreststands
with rich shrub layer because reduce the availability of
open ground.Positive correlation with densities of
species nesting in the canopy and average tree basal
area was explained bySherryandHolmes(1985).
They state that the tree basal area is a good index for es

timating the leaf surface of the tree which should be important
factor for species inhabiting canopy.

It can be concluded that for habitat selection of forest
birds on the larger spatial scale both floristic and
structural composition are important, while on smaller
scale the differences in structural characteristics had
higher impact to bird communities than floristic differences.
Structural characteristics related to forest age
had the most pronounced effect to the densities of different
ecological groups of birds.

Research of forest bird communities were fundedberak – Samoborsko gorje.
by Nature Park Medvednica and Nature Park Žum-

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