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The main goal of this study was to determine the reason for the significant increase of the tawny owl Strix aluco population in Kozłówka Forest near Lubartów (51°30' N, 22°35' E) in eastern Poland. Since 1990, this forest complex has been part of Kozłowiecki Landscape Park. Our research was conducted using standard playback method on a sample plot covering 50 km2. Each year in March and April 1990-91 and 2007-09, three counts with vocal stimulation were performed on the study plot. Between 1991 and 2009, a significant increase in the density of the tawny owl population was observed from 2.4 pairs/10 km2 to 4.6 pairs/10 km2. We discuss how habitat quality, food availability, and weather conditions can explain this phenomenon.
Unsuitable forest management is a widespread and
common threat facing many forest bird species. Forestry
practices modify the original structure of most European
forests and promote changes in tree age and species com-
position [1, 2]. The changes in vegetation structure and
resource availability have a major impact on wildlife popu-
lations [3]. The present forestry reduces the availability of
old trees, dead wood and tree cavities [4]. Owls breeding in
woodlands are especially vulnerable because of their low
numbers and specific habitat requirements. Recently in
Poland, the introduction of reduced impact logging in for-
est management systems was proposed in some areas. This
system is based on retention of cavity-bearing trees and
selective harvest in forestry practice. The implementation
of this programme led to management more suitable for
hole-nesting forest birds, because it focused on the conser-
vation of old trees with nest-holes and provisioning of nest
boxes (also for owls). Unfortunately, in most of cases this
practice can be unsatisfactory in owl protection, because
most owl species need larger holes in natural areas with
good habitat conditions.
We analyzed tree age composition changes and
observed that the proportion of stands over 80 years old
increased during the study period. Therefore, we may
expect that the above-described changes can significantly
improve habitat conditions for the tawny owl in the study
area. In this analysis, we also control the impact of winter
conditions and potential food resources on the population in
our study area.
Tawny owls breed throughout most of Europe [5-6].
This species is the most common owl in Poland [7], but
there has been a lack of long-term studies on changes in the
Polish J. of Environ. Stud. Vol. 19, No. 5 (2010), 1039-1043
Original Research
The Role of Forest Age, Habitat Quality,
Food Resources and Weather Conditions
for Tawny Owl Strix aluco Populations
Jarosław Wiącek1*, Marcin Polak1, Grzegorz Grzywaczewski2
1Department of Nature Conservation, Maria Curie-Skłodowska University,
Akademicka 19, 20-033 Lublin, Poland,
2Department of Zoology, University of Life Sciences in Lublin,
Akademicka 13, 20-950 Lublin, Poland
Received: 27 November 2009
Accepted: 12 April 2010
The main goal of this study was to determine the reason for the significant increase of the tawny owl
Strix aluco population in Kozłówka Forest near Lubartów (51°30' N, 22°35' E) in eastern Poland. Since 1990,
this forest complex has been part of Kozłowiecki Landscape Park. Our research was conducted using standard
playback method on a sample plot covering 50 km2. Each year in March and April 1990-91 and 2007-09, three
counts with vocal stimulation were performed on the study plot. Between 1991 and 2009, a significant increase
in the density of the tawny owl population was observed from 2.4 pairs/10 km2to 4.6 pairs/10 km2. We dis-
cuss how habitat quality, food availability, and weather conditions can explain this phenomenon.
Keywords:tawny owl, Strix aluco, population trends, owl conservation
abundance of this species [8]. The breeding density of
tawny owl populations has been studied in different habitats
in Poland [9]. It is common mostly in deciduous and mixed
old forests, reaching densities of 10-20 pairs/10 km2. In
coniferous forests and agricultural landscapes its density is
1-10 pairs/10 km2. Its total number in Poland is estimated to
be 65,000-75,000 pairs [10]. Despite this, knowledge about
the number and distribution of this species in Poland is not
sufficient, especially in respect to long-term changes in
The aim of this study was to determine reasons for the
increased number of the tawny owl population in Kozłówka
Forest and to understand how the tawny owl responded to
the aging of forests and improving quality of habitats,
including weather conditions during the time of study.
Experimental Procedures
Study Area and Forest Management Changes
We examined the effects of aging forests, rodent cycle
stages (based on Quercus sp. seeds productivity), habitat
quality and weather conditions (temperature from
December to February and days with snow fall) on the
entire number of tawny owls in Kozłówka Forest near
Lubartów (51°30' N; 22°35' E) in eastern Poland. This for-
est complex was part of the Zamojscy estate. The surface of
the study area was 41 km2in 1990 and 50 km2in the fol-
lowing study seasons (1991 and 2007-09). The data from
1990 were excluded from further analyses because they had
a preliminary character and were obtained from a smaller
plot. The dominant form was pine (78%) and oak (13%)
stands. Habitats of the study area consisted of pine forest
(70%), hornbeam (20%) and alder (10%) [11]. Generally,
this proportion did not change between the 1991 and 2007-
09 seasons. We used information based on the number of
breeding territories gathered in 1991 and 2007-09. In the
last three seasons the studies were conducted based on the
high vole and mice number conditions (unpublished data
from State Forest Inspectorates Lubartów). Between these
two periods, the forest and owls conservation procedures
changed significantly. In order to preserve this forest com-
plex, the Kozłowiecki Landscape Park was established in
1990. During the last two decades, the age structure of the
forest changed. The share of the old-growth stands (81-120
years old) in the study plot increased from about 24% to
35% (Fig. 1). In 2001, twelve nest boxes for tawny owls
were placed on the study area by forest managers. All nest
boxes were checked once in April 2007 to find signs of use
by owls such as pellets, feathers, and prey remains, with
adult owls or eggs.
Sampling Methods
The sampling methods were the same in 1991 and
2007-09. We visited the entire sample plot three times dur-
ing one breeding season (February, March, and April) using
a nocturnal vocal stimulation with standard playback tech-
nique [12, 13]. During each visit, one to five groups of
observers were present in the field. Playback sessions of the
male “hoot” calls lasted 6 minutes (3 minutes of broadcast-
ing and 3 minutes of listening). Playback stations were
located at approximately 200 m intervals along the transect
routes. During all seasons, the same kind of male territorial
call was used. All observations were noted on official
forestry planning maps at 1:25,000 scale. Observations
were conducted in stable weather without strong winds and
rainfall. Meteorological conditions were obtained from from Radawiec Meteorological
Station (N 51°13'; E 22°23') located 20 km from our study
area. The preference of owls for stands in six age classes
(Fig. 1) was tested using the chi-square test. We analyzed
the role of forest age when comparing the potential habitats
and the nesting places.
Results and Discussion
Between 1991 and 2009 a significant increase of densi-
ty in the tawny owl population was observed from 2.4
pairs/10 km2to 4.6 pairs/10 km2(Table 1). In 1991 there
were 12 pairs on the study plot. The highest number of pairs
during the study period was recorded in 2009 – totaling 23
pairs (Table 1). Changes in the number and distribution of
breeding pairs between 1991 and 2007 is presented in Fig.
2. Among the 12 boxes placed in the study area in 2000, 7
boxes (58.3%) were already used by tawny owls before
2007. However, in the 2007 breeding season only one nest
1040 Wiącek J., et al.
Fig. 1. A comparison of age forest classes between 1981-90 and
1991-2000 in Kozłówka Forest.
Year Study area
of pairs
(pairs/10 km2)
1991 50 12 2.4
2007 50 22 4.4
2008 50 19 3.8
2009 50 23 4.6
Table 1. The number and density of tawny owls in Kozłówka
Forest in 1991 and 2007-09.
box was used for breeding. In the following two seasons
none of the boxes were used. The analysis of preferences to
different age forest classes has shown a significant prefer-
ence of this species for older stands (χ2=105.3, df=5,
P<0.0001). In both study periods (1991 and 2007) most ter-
ritories were located in the oldest stands (>100 years) -
45%, following 27.5% for 81-100 years old and then
27.5%. for 61-80 years old. Changes of habitat selection
during the study period is presented in Table 2. In the
mature oak stands, the number of territories was stable dur-
ing the study period. However, we observed significant col-
onization of pine forests by tawny owls. The weather data
shows that in both study periods of 1991 and 2007-09,
weather conditions were similar. In both season, the snow-
falls were less intensive than during other winters (Fig. 3).
In these seasons, temperatures were higher in comparison
with typical Polish winter conditions (Fig. 4). These
weather traits were probably optimal for breeding owls.
A few seasons before the first study year, 1991, were poor
in oak seeds, while years prior to the second study period,
2007-09, were rich (Fig. 5). Seeds of oaks are the main food
for forest mice species such as Apodemus sylvaticus and A.
flavicollis, the main prey for the tawny in the study area
[31]. Oak masts are the main food of forest species of mice
Apodemus sp. and voles Microtus sp. Breeding density of
the tawny depends strongly on the density of small rodents
[17]. This data suggests that the first survey (1991) was
made in poor provisioning conditions for rodents, while the
following surveys (2007-09) were made during good food
conditions. Therefore, at the beginning of the 1990s, food
availability for owls might have been limited, while in the
last seasons (2007-09) availability of prey was rather high.
The Role of Forest Age, Habitat Quality, Food Resources... 1041
Habitat % habitat
Number of
territories in
1991 (%)
Number of
territories in
2007 (%)
Pine forest 70 6 (50) 16 (72)
Hornbeam 20 6 (50) 5 (23)
Alder 10 01 (5)
Table 2. The comparison of the habitat selection between 1991
and 2007 in Kozłówka Forest.
Fig. 2. Number and distribution of tawny owl territories in 1991
and 2007 in Kozłówka Forest.
1991 2007
Fig. 3. Days with snowfall as cumulated index for December,
January, and February (1981-2008).
1990 2007
temperature ºC
Fig. 4. Mean temperature as cumulated index for December,
January, and February (1981-2008).
seeds of Quercus (kg)
1993 1997 2001 2007
Fig. 5. The seasons with high seed production (Quercus sp.) in
Kozłówka Forest.
The main result of this study was to verify the significant
increase in the tawny owl population. The Polish population
of this species increased in cities since the 1960s [14]. The
following data gathered in the 1970s and 1980s confirmed
the stability of this trend in the density of the tawny in large
towns [15, 16]. Lack of data from forest territories in Polish
literature from recent years makes the estimation of trends in
the forest habitat problematic. The only data for comparative
analyses of changes or trends in the breeding density of the
tawny in this habitat comes from our study. Significant
increase of the number of tawny owls in the forests of
Central Europe was reported by Hagemeijer and Blair [7].
Much data from France, Belgium, Luxembourg,
Netherlands, Germany, and Finland indicates an increase in
the number of breeding pairs [17]. Some rudimentary infor-
mation about changes in breeding density of this owl in east-
ern Poland can affirm that the tawny population significant-
ly increased [18, 19].
The density of the tawny as compared to other raptors
depends on food abundance and cycles in populations of
their prey. Many authors have reported strong correlation
between the breeding density of the Tawny and the num-
bers of their prey [6, 17]. Fluctuations between the number
of breeding pairs in the following years increased by 30%
as a consequence of prey availability [20], but the increase
recorded in our population was much higher than this value
and cannot be explained only by small mammals’ regular
cycles. Polish ornithological data confirm that the year
1991 was good for other raptors such as the short-eared owl
Asio flammeus and other predators feeding on small mam-
mals like mice or voles [21, 20], similar to 2007-09, when
our research in Kozłówka Forest was repeated (forest
inspectorate data).
The breeding density of the tawny owls from Kozłówka
Forest in 1991 was 2.4 pairs/10 km2. This data is situated as
a mean value for pine forests in Poland where breeding den-
sities in the 1980s changed from 2 pairs/10 km2[22] to 5
pairs/10 km2[23]. However, data from 2009, when the
breeding density was 4.6 pairs/10 km2, showed that nesting
conditions for this owl improved significantly. The age of
forest stands is important for the nesting of the tawny in
Kozłówka (Fig. 1). This positive change in the environment
caused an increase in the density this species of owl in the
study area. Most published data underline a strong relation
between breeding density and the age of forest stands in the
tawny owl habitat [5, 6, 17, 23, 24]. Additionally, providing
nest-boxes can help with strong colonization, in young,
suboptimal pine habitats in the study area. Such a situation
was described by Gramsz et al. [8]. Nest boxes placed in
comparatively young forest stands can make possible nest-
ing of the tawny owl. Unfortunately, nearly half of the nest
boxes in the study area were unsettled because they were
located near optimal habitats with natural holes. Natural
holes are probably more attractive for birds, therefore most
boxes near occupied territories were empty. The strong ter-
ritoriality of the tawny made it impossible to colonize these
boxes by other birds. Changing their location to far from
occupied territories makes possible settling by new pairs. On
the other hand, some authors underlined that too great a
number of nest boxes for the tawny owl increase their neg-
ative impact on other rare species of owl, such as the
pygmy owl Glaucidium passerinum, the little owl Athene
noctua or Tengmalm’s owl Aegolius funereus [8]. Some
data confirmed that the Tawny is increasing its density, dis-
placing the barn owl Tyto alba in the agricultural landscape
of eastern Poland [19].
In 1991 and 2007-09, a quick increase in the number of
territories in the pine forest was recorded. But the number
of the hornbeam territories was stable. In the situation of
low (1991) and high (2007-09) densities in the following
seasons, all available hornbeam territories were occupied
(5-6). New pairs came to settle only in pine or alder wood.
Therefore, strong growth in the numbers of territories was
only observed in the pine forest. This preference in order of
settlement in a different habitat was described in literature.
Tawny owls nest in different habitats but prefer old, broad-
leafed forest [25]. Therefore, breeding densities recorded in
hornbeam habitats (usually above 5 pairs/10 km2) were sig-
nificantly higher in comparison with habitats in pine woods
[11, 26-30].
The age of tree stands in the study area significantly
changed between the 1991 and 2007-09 seasons. But a
strong increase in the number of pairs probably had an
effect on other factors too. Many authors underlined that
weather conditions can influence the breeding density in
many owl species [6]. Data from Poland (Białowieski
National Park) suggest that mild winters with small snow-
fall can help with the survival of small mammals and their
detection by raptors [20]. During the time of our study in
Kozłówka Forest, the tawny population was monitored in
the comparatively mild winters in comparison to, in gener-
al, harsh Polish winter conditions. Additionally, a small
number of days with snow fall was observed in the study
seasons. These factors can help with high hunting success
and high density breeding in both study seasons. However,
a much lower breeding density observed in the 1991 season
was the effect of strong winter conditions in former years
(1985-87) when the tawny population probably decreased
strongly (Figs. 3 and 4). This phenomenon was compared
with tawny counts in Kozłówka forest in 2010, when after
a harsh, snowy and long winter we recorded their decline in
a number of territories (our unpublished data).
The present forest management in Poland is based on
protection of old trees with natural holes. Theoretically, this
system can favour highly territorial and sedentary species
such as the tawny. A few old trees with holes remaining in
the clearing areas can provide a safe nesting place for this
owl. In practice, the reduced impact of logging was proba-
bly not a main reason for the strong increase of pair num-
In summary, the number of breeding pairs of the tawny
owl in the study area significantly increased since the
1990s. The main reasons for this increase were the aging of
the forest, connected with improvement of habitat quality.
The number of breeding pairs depended on good weather
1042 Wiącek J., et al.
conditions and food abundance. The presence of nest-boxes
and the reduced impact of logging in forest practices cannot
significantly help in density increase of the tawny owl in
the study area. We need data from the plots located in other
regions of Poland to determine the true trend in Tawny Owl
population changes throughout the country.
We are grateful to Beata Niedźwiedź, Diana
Płudowska, Kalina Łapińska, Paweł Łapiński, Małgorzata
Patyniak, Waldemar Gustaw, Piotr Karpiński, Magdalena
Małkowska, and other students from Maria Curie-
Skłodowska University and the University of Life Sciences
in Lublin and State Forest Inspectorates Lubartów for their
help during the fieldwork.
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The Role of Forest Age, Habitat Quality, Food Resources... 1043

Supplementary resource (1)

... Die Reviergrösse beim Waldkauz ist nebst alten Baumbeständen mit stehendem Totholz auch abhängig von offenen Landflächen (Nagl, 2015;Marchesi et al., 2006, S. 310-318), dem Höhengradienten (Salvati & Ranazzi, 2002, S. 237-243) sowie klimatisch bedingten Faktoren (Wiącek et al., 2010(Wiącek et al., , S. 1039(Wiącek et al., -1043. Im Gegensatz dazu sind reine Nadelwälder für den Waldkauz weniger geeignete Habitate (Aebischer, 2008, S. 214;Nagl, 2015). ...
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The key figures of the tawny owl breeding pairs in different countries are difficult to compare due to the different reference values. Based on the respective forest areas, a more reliable key figure can be calculated for the number of breeding pairs per 100 square kilometers. Die Kennzahlen der Waldkauz Brutpaare unterschiedlicher Länder lassen sich auf Grund unterschiedlicher Bezugsgrössen schlecht vergleichen. Anhand der jeweiligen Waldflächen kann eine verlässlichere Kennzahl berechnet werden für die Anzahl Brutpaare pro 100 Quadratkilometer.
... Table 2. Results (F value and significance) of generalized linear models (GLM, two-way ANOVA) used to test for differences in home range areas (95%, 70% and 50% MCP) and territory size (100% MCP) of radio-tracked Tawny Owls between the two study areas, both sexes, and these factors combined. These include the ageing of the forest, which is connected with improvement of habitat quality (Wiącek et al. 2010). This factor may explain our case better than the previous two and will be tested in further studies. ...
Over a two-year period (2013-2015), we trapped and radio-tracked 20 Tawny Owls at two study sites in northern Spain. We obtained 4257 radio-tracking locations, 328 of which were associated with vocal activity. Home ranges were significantly different between the two study sites (95% minimum convex polygon (MCP) = 125.79 ha vs. 95% MCP = 50.96 ha). Territory size was significantly less than 95% MCP home ranges and not significantly different from 70% MCP home ranges at both study sites, but was significantly larger than 50% MCP home ranges in the second site. Locations with vocal activity tended to be significantly closer to the home range border than random non-vocal locations. However, Tawny Owls focused vocal activity over the 50% MCP and close to the border of 70% MCP at both study sites. Home ranges were not significantly different between sexes for any of the three spatial scales, but male territories were significantly larger than female territories. The vocal behaviours of some owls, mainly females, were negligible or anecdotal (less than five vocalizations detected during the study period), and female territories were significantly smaller than male territories. ARTICLE HISTORY
... Das Fehlen von geeigneten Brutbäumen kann der Waldkauz allerdings auch durch Freibruten kompensieren (Hartung, 2006, S. 376-379;Melde, 1984). Die Reviergrösse beim Waldkauz ist nebst alten Baumbeständen mit stehendem Totholz auch abhängig von offenen Landflächen (Nagl, 2015;Marchesi et al., 2006, S. 310-318), dem Höhengradienten (Salvati & Ranazzi, 2002, S. 237-243) sowie klimatisch bedingten Faktoren (Wiącek et al., 2010(Wiącek et al., , S. 1039(Wiącek et al., -1043. ...
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Die Dispersion vom Waldkauz (Strix aluco) wurde in Europa anhand von Beringungsdaten untersucht. Aus der EURING-Datenbank resultieren insgesamt 37 893 Ringfunde von Waldkäuzen in der Zeitperiode von 1910 bis 2015. Für die statistische Auswertung standen Daten von 6 725 adulten, 21 845 juvenilen, 1 935 männlichen und 6 670 weiblichen Waldkäuzen zur Verfügung. Untersucht wurden die Dispersions-Unterschiede in der Distanz und der Richtung von juvenilen/adulten wie auch männlichen/weiblichen Waldkäuzen. Zudem wurde die vertikale Dispersion und der Einfluss der Klimaerwärmung geprüft. Je nach Fragestellung kamen andere Selektionskriterien zum Tragen. Die statistische Auswertung erfolgte mit IBM SPSS Statistics; das Kartenmaterial wurde mit QGIS erstellt. Bei den Distanzen zeigen sich deutliche Unterschiede zwischen Geschlecht und Alter. Die juvenilen Waldkäuze dispersieren deutlich weiter als die adulten Waldkäuze (t(15 131) = -37.765, p = 0.000). Ebenfalls unterscheiden sich die Dispersionsdistanzen bei den Männchen und Weibchen. So dispersieren die Weibchen signifikant weniger weit als die Männchen t(8 609) = 2.103, p = 0.035). Die Brutgrösse beeinflusst nur bedingt die Dispersionsdistanz. Die Distanzen steigen zwar mit zunehmender Brutgrösse an, sinken allerdings wieder bei Brutgrössen mit sechs oder mehr Jungvögel. Der Vergleich der Dispersionsrichtung in einzelnen Ländern zeigt, dass es beim Vergleich je zweier Länder sehr unterschiedliche Resultate gibt. So zeigen 11 Länderpaarungen ähnliche Verteilungsmuster, während bei 17 Länderpaarungen signifikant unterschiedliche Verteilungsmuster vorliegen. Mehrheitlich unterscheiden sich also die Richtungen in einzelnen Ländern, was einen regionalen Trend der Richtung vermuten lässt. Es gibt sowohl signifikante Unterschiede zwischen den Geschlechtern (U20.052, p > 0.50), wie auch zwischen dem Alter (U20.243, 0.02 > p > 0.01). Obwohl die Verteilung in beiden Fällen nicht uniform ist, besteht keine eindeutige Hauptrichtung. Bei der vertikalen Dispersion beeinflusst der Breitengrad und die Höhe über Meeresspiegel die Höhendifferenz. Die berechnete Regressionsgerade (∆h = 169.917 - 2.781·Breitengrad - 0.115·Höhe über Meeresspiegel) zeigt: Je nördlicher der Breitengrad und je höher die Höhe über Meeresspiegel, desto mehr wird in tiefergelegene Regionen dispersiert. Dabei hat der Breitengrad einen grösseren Einfluss als die Höhe über Meeresspiegel. Bei der vertikalen Richtung dispersiert die Mehrheit der Waldkäuze in tiefere Lagen. Besonders ausgeprägt ist dies ab einer Höhe von 600 m.ü.M der Fall. Die Klimaerwärmung der letzten 105 Jahre hat keinen Einfluss auf die Dispersionsdistanz. Es sind zwar periodische Schwankungen der Distanzen erkennbar, aber keine kontinuierliche Veränderung. Ab dem Jahr 2000 weisen die Schwankungen aber grössere Ausschläge auf als in früheren Jahren. Eine eindeutige Besiedelung neuer nördlicher Gebiete konnte in Fennoskandien nicht belegt werden, da der Median der Breitengrade periodisch schwankt. Seit 1990 ist allerdings ein leichter Aufwärtstrend erkennbar. Die vorliegende Arbeit verdeutlicht die Unterschiede im Dispersionsverhalten von juvenilen/adulten und männlichen/weiblichen Waldkäuzen. Ebenfalls beeinflusst das Klima und die Topografie die Dispersion des Waldkauzes. Die stark regional abhängigen Dispersionsmuster erklären auch die zum Teil unterschiedlichen oder sogar gegensätzlichen Ergebnisse anderer Studien. So können unterschiedliche Studiengebiete nur bedingt miteinander verglichen werden. Insbesondere ist dann Vorsicht geboten, wenn die Studien auf unterschiedlichen Gruppeneigenschaften basieren. Für weitere Studien, welche das Ziel verfolgen, die Dispersion des Waldkauzes zu analysieren, können zwei zentrale Prämissen formuliert werden. Erstens bedarf es bei der Untersuchung von Populationsstudien zwingend Datensätze von Weibchen und Männchen, sowie Jung- und Altvögeln. Die Auswertungen sind jeweils immer in allen Ausprägungen einzeln zu beurteilen. Nur so werden Verzerrungen durch andere Ausprägungen verhindert. Zweitens ist die Grösse des Untersuchungsgebietes entscheidend für dessen Aussagekraft. Riesige Untersuchungsgebiete weisen immer auch unterschiedliche Einflussfaktoren auf. Deshalb haben Populationsstudien eine stärkere Aussagekraft, wenn sie sehr regional angelegt sind. Denn die möglichen Einflussfaktoren sind dann mehrheitlich identisch und ein effektiver Vergleich ist durchführbar. Unter diesen Umständen wäre es durchaus denkbar, dass regional eindeutige Trends in Richtung und Distanz belegt und erklärt werden könnten.
... The tawny owl Strix aluco is the most common and numerous owl species in Europe [1] and in Poland [2]. The species is well adapted to inhabit a wide range of landscapes, i.e. woodland, rural and urban environments. ...
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Established taxa within the Enterobacteriaceae wereisolated from cloacal swabs of Strix aluco chicks in nest boxes located at five research sites. ChromID ESBL medium (bioMerieux) was used to select a pool of Enterobacteriaceae strains producing extended-spectrum beta-lactamases. Drug sensitivity of the chosen strains was determined from the full pool of Enterobacteriaceae to 6 chemotherapeutics of different mechanisms of action. The study evaluated the sensitivity of ESBL-synthesizing isolates to substances belonging to penicillins, cephalosporins, cephamycins, clavams, carbapenems and monobactams. Analysis of the results indicated a potential role of Strix aluco in the dissemination of epidemiologically-relevant Enterobacteriaceae, and, importantly, pose health risks to forest service workers, nature protection service and ornithologists. The results can also serve as the basis for further environmental studies.
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Our aim was to determine dynamics in a population of tawny owls Strix aluco over 15-year period, in relation to year-to-year variation in environmental conditions. The research was carried out in a habitat mosaic of fields and forest in central Poland, over the 2004−2018 period. Numbers of pairs (territories) were established by the standard playback survey technique supplemented by searches for nest sites. The selected environmental factors studied in parallel were the acorn production, density changes in field and forest rodents, meteorological conditions in winter and density of martens (Martes spp.). At the start of the study period 20 nest boxes designed for tawny owls were placed out in the study area. This number was enlarged by additional 27 nest boxes placed in 2012. The number of owls in the area remained stable-in the range of 26−29 pairs, despite changes in nesting sites availability. However, moderate influence of rodent density and winter conditions on population abundance was detected. Also, peak in the rodent population coincided with greater clutch size and numbers of young owls reared. Densities of martens remained relatively stable throughout the study period, and there were no reported cases of these carnivores killing tawny owls, despite the former taking shelter in the owl-boxes. ARTICLE INFO Regular research paper Pol.
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The study on the abundance, distribution and habitat selection of selected species of Owls (Strigiformes) described in this article was conducted in 2016 and 2017 in Kozłówka Forest, situated near Lublin (51º 30’ N, 22º 35’ E) in eastern Poland. Kozłówka Forest is part of the Kozłówka Landscape Park (established in 1990) and it’s a typical commercially used tree coverage. 70% of its area is covered with coniferous and mixed forests, 20% with deciduous forests. Approximately 70% of tree stands were more than 60 years old.The total area in which the study was conducted was 55 square km.. The research was carried out with the use of the standard playback method and covered the following species: Eagle Owl (Bubo bubo L.), Pygmy Owl (Glaucidium passerinum L.), Little Owl (Athene noctua Scopoli), Tawny Owl (Strix aluco L.), Ural Owl (Strix uralensis L.), Long – Eared Owl (Asio otus L.) and Tengmalm’s Owl (Aegolius funereus L.). Tawny Owl Strix aluco was the only species detected.Its 27 territories were detected in 2016 and 34 in 2017. Overall density of was 4,9 territories /10 km2 in 2016 and 6,18 territories /10 km2 in 2017, both comparable to the species’ typical density in coniferous woodlands in Poland and Europe. The lack of other owls’ detection probably resulted from the deficiency of suitable habitats in Kozłówka Forest, strong general decline of certain owl species in Poland, as well as several methodical difficulties.
The risk of overestimating the number of nocturnal owls during a census is substantial when the territory density is high and no individual signature is available. The tawny owl voice was demonstrated to be individual, but no statistical technique evaluated to date is suitable for a census of this species. To overcome the problem, the combination of two methods is suggested in this study: (1) the Visual Spectrographic Comparison (VSC), a bioacoustics tool which tries to separate owls’ voices classifying the spectrograms of their calls based on their visual characteristics, and (2) the extensively used technique of Mapping Method (MM). The technique was applied to a dense population of tawny owls living in an isolated deciduous wood of northern Italy. Fourteen territorial males were individuated in the area, resulting a density of 6.0 pairs/km². Most of the home ranges seem to overlap substantially, an evidence not in step with the common idea of high territoriality of the species. Since the technique is believed to be exhaustive, a future monitoring of this population could be precise, cheap and very informative. This technique could be easily extended to other elusive species that show individual vocal cues.
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Słowa kluczowe: Strix aluco, zagęszczenie, pokarm, pogoda, gospodarka leśna. Analizowano wpływ na liczebność badanej populacji puszczyka Strix aluco takich czynników, jak: intensywność prac leśnych, typ siedliska, dostępność pokarmu, temperatura oraz liczba dni z opadami śniegu. Cenzusy populacji puszczyka prowadzono z wykorzystaniem standardowej metody stymulacji głosowej w latach 2007–2014 na powierzchni 50 km 2 , zlokalizowanej w La-sach Kozłowieckich koło Lublina (51°30′N, 22°35′E), na terenie Nadleśnictwa Lubartów (RDLP Lublin). Dominującym gatunkiem drzewostanów na całej powierzchni badawczej była sosna zwy-czajna. Bory porastały 70% powierzchni, a 20% grądy. W każdym sezonie od lutego do kwietnia wykonano trzy nocne kontrole. Stwierdzono łącznie 181 terytoriów puszczyka. Wykazano zna-czące fluktuacje zagęszczeń terytoriów pomiędzy kolejnymi sezonami. Liczba terytoriów wahała się w poszczególnych latach od 3,8 do 6,2/10 km 2. Mimo przewagi siedlisk borowych na analizo-wanej powierzchni puszczyki preferowały grądy. W latach z intensywnymi opadami śniegu oraz niskimi temperaturami (2010 i 2013) liczba zajętych terytoriów była niższa, jednak zależność ta nie była istotna statystycznie. Podobnie gospodarka leśna nie miała znacząco negatywnego wpły-wu na liczebność terytoriów puszczyków. Ponad połowa (54%) zajętych terytoriów znajdowała się w sąsiedztwie miejsc, gdzie prowadzono prace leśne (rębnie i trzebieże). W latach nasiennych dębów (2009, 2011 i 2012), kiedy drobne gryzonie (podstawowy pokarm puszczyków) miały pod dostatkiem pokarmu, liczba terytoriów była wyższa. Spośród wszystkich analizowanych czynni-ków jedynie obfitość pokarmu związana z latami nasiennymi dębów miała wpływ na zagęszczenie lęgowej populacji puszczyków (r = 0,98, p = 0,000015).
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The diet composition of the Tawny Owl Strix aluco breeding in the Kozłówka Forest in eastern Poland was analysed. Materials were collected from seven nest-boxes in 2007. The material contained the food remains of 24 species: twelve rodent, two insectivore, one bat, three bird, two fish, as well as three insects and frogs. Among 286 identified prey items, small mammals were represented as dominant group in a food (78.7%). Frogs to made 13.6% all of prey, birds (2.8%), fishes (1.7%), insects (3.2%). The main components of food were forest species of rodents (Apodemus and Clethrionomys). Frogs and fishes in the food were only presence in the wet territories with fish ponds and meadows in the small river valleys. Food from the Kozłówka forest contained 8.5% fishes by biomass. To our knowledge, it is the highest level of this food component recorded in European literature.
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1. The aim of this study was to examine tawny owls Strix aluco in continuous and fragmented woodland habitats to determine the effect of fragmentation on behaviour, breeding success and turnover. 2. Information on home range and territorial behaviour was obtained from 23 radio-tagged individuals. Eight of these were in one large wood (continuous) and the rest in an area containing < 0.5% woodland (fragmented). Measures of breeding success and turnover were assessed in up to 67 territories in woods ranging from 0.1 ha to 196 ha. 3. Owls occurred in all woods > 4 ha and in up to 45% of wood < 4 ha. 4. Home range size was inversely related to wood size. For male owls, wood isolation and wood size accounted for 80% of the variation in horne range size. 5. In the fragmented woodland area tawny owl home ranges contained more woodland than expected from random. Within horne ranges, usage of habitat was such that woodland > buildings > grassland > arable areas. Owls utilized the grassland and arable areas by hunting from the ground. 6. In continuous woodland owl horne ranges overlapped more and they were more often involved in territorial behaviour than those in fragmented woodland. 7. There was a negative relationship between small mammal abundance and wood size. 8. For all years combined there was a quadratic relationship between wood size and breeding success, suggesting that owls perform better in intermediate-sized woods. 9. Turnover was highest in the smallest woods and lowest in the intermediate woods. 10. It is concluded that the intermediate woods, where food is abundant and energetic costs are not great, present an optimum habitat for tawny owls in this area. 11. The study indicates that data on breeding success and turnover are essential in determining the effects of habitat fragmentation and that these effects may not be easy to predict, given information from non-fragmented areas.
Density of Strix aluco was 4.7-5.6 pairs/10km² of the forest area, whereas in old tree stands it was 13.0 pairs/10km². Athene noctua occurred only in the vinicity of a village; this species was not recorded on meadows, with density 0.6 pairs/10km² of the total area and 1.5 pairs/10km² of woodless areas. Asio otus occurred only on dense woodland areas with a density of 3.5 pairs/10km² of the total area and 4.3 pairs/km² of the forest. -from English summary
In 1977-1980 the breeding population of tawny owl was censused in three plots. Density varied between 5.5-14.9 pairs/km². High lability of territories was found, with single males and females holding their own territories. Average territory size for 11 pairs was 61ha (30-93ha). -from English summary
Calculated a density of 1.2-1.6 pairs/10km² in the centre of the city and 0.8-1.0 pairs/10km² in the whole city area. The total number of tawny owls in Warsaw (485km²) was c40-60 pairs. During the last 20-30yr, tawny owl density has increased. -from English summary
In farmland (80km 2) the density fo Strix aluco was 1.0 pair/10km 2 (4.5 pairs/10km 2 of forest); Asio otus: 0.6 and 2.8 respectively; Athene noctua and Tyto alba, 0.4 pairs/10km 2. In a forest areas the density of Strix aluco was 2 pairs/10km 2; Asio otus, 0.4 pairs/10km 2. Distribution of Strix aluco was irregular and it was connected with old tree stands, Asio otus was distributed evenly, although preference towards the edge in large forest was evident. -from English summary
We correlated breeding density and proportion of wooded area per territory of Tawny Owl Strix aluco measured in four deciduous forest types with forest elevation and song-bird abundance, both regarded as estimators of forest productivity. The proportion of wooded area was positively correlated to forest elevation, being low in coastal thermophilous oak woods and increasing in hilly mesophilous oak woods and in mountain beech woods. Songbird abundance showed a reverse pattern as the proportion of wooded area per owl territory was negatively correlated to songbird abundance. No correlation was observed between these variables and the breeding density of owls. The low proportion of wooded area per territory in coastal thermophilous oak forests likely depends on that this wood type provides old trees with suitable cavities for nesting and large prey availability, thus representing the optimal habitat for the Tawny Owl in central Italy. We suggest that wooded area per owl territory may be used to predict the quality of different forest types.
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