Magpie Pica pica nest sites in farmland in

Jerzak L., Kavanagh B.P., Tryjanowski P. (red.)
Ptaki krukowate Polski [Corvids of Poland]
Bogucki Wyd. Nauk., Poznań 2005
Grzegorz Orłowski
Magpie Pica pica nest sites in farmland in vicinity
of Wrocław city (SW Poland)
Gniazdowanie sroki Pica pica w krajobrazie rolniczym
okolic Wrocławia
ABSTRACT: In winter 2001/2002 in intensively managed farmland (57.5 km ; 91% occupy
by arable land) in the in vicinity of Wrocław city (Lower Silesia Province, south-western Poland) 56 nests of Magpie Pica pica were found. Eighty-two percent (46 nests) were located in
the villages. The remaining 10 (18%) were found in open agricultural areas. The mean density of nests in built-up areas was 53 times higher that in crop fields (10.1 pairs/km2 – villages vs. 0.19 pairs/km2 – open farmland). Nests were found in 24 of 26 settlements examined. Density in particular settlements ranged from 0 to 200 pairs/km2. Nests were located
on 14 tree and 2 bush species. Nearly 22% of the nests were located in poplar trees Populus
spp. The mean height of nests location in village areas was nearly twice that in open farmland (mean ± SD = 11.1 ± 3.7 m in villages vs. 5.7 ± 2.9 m in open farmland). Compared
previous data from 1977–79 originating from an area of 15.8 km2 situated in the middle part
of the area studied, a 2–3-fold decrease in magpie population was recorded (decrease in density, from 0.63–1.07 to 0.32 pairs/km2 in the respective period). This would indicate a withdrawal of the species from open agricultural areas, while remaining at the former level in villages.
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KEY WORDS: Magpie, Pica pica, nest sites, farmland birds, agricultural intensification
STRESZCZENIE: W ostatnich kilkudziesięciu latach na terenach zurbanizowanych Europy
zanotowano znaczny wzrost liczebności sroki. Dane z krajów Europy zachodniej jak i Polski
wskazują także na wzrost liczebności sroki na obszarach wsi, przy równoczesnym wyraźnym
spadku liczebności w obrębie agroekosystemów, skąd gatunek ten wycofuje się. W krajach
Grzegorz Orłowski, Department of Agricultural Bases for Environmental Management,
Agricultural University of Wrocław, pl. Grunwaldzki 24, 50-363 Wrocław. Poland, e-mail:
[email protected]
510
Grzegorz Orłowski
Europy zachodniej regres liczebności sroki w obrębie pól uprawnych obserwowany jest od
lat sześćdziesiątych XX wieku. Współcześnie, w wielu rolniczych rejonach Europy zachodniej sroka już nie występuje.
Zimą 2001/2002 roku na intensywnie użytkowanej rolniczo powierzchni (57,5 km2, w tym
91% zajmowały pola uprawne) położonej w okolicach Wrocławia (południowo-zachodnia
Polska) zlokalizowano 56 gniazd sroki. Spośród 26 skontrolowanych osiedli gniazda sroki
stwierdzono w 24 (92%) z nich. Średnie zagęszczenie gniazd na obszarze zabudowanym
było 53-krotnie wyższe w porównaniu z terenami rolniczymi (10,1 pary/km2 – wsie vs. 0.19
pary/km2 – tereny rolnicze). Gniazda ulokowane były na 13 gatunkach drzew i krzewów.
Średnia wysokość umieszczenia gniazd na terenie wsi była blisko dwukrotnie wyższa w porównaniu z otwartym krajobrazem rolniczym.
W porównaniu z latami 1977–1979, na 15,8 km2 powierzchni zlokalizowanej wewnątrz obszaru badanego na przełomie lat 2001/2002, zanotowano 2–3-krotny spadek zagęszczenia
populacji lęgowej sroki. Gatunek ten wycofał się głównie z terenu pól uprawnych, a pozostał
w niezmienionej liczbie we wsiach. Podobnie jak w przypadku innych gatunków ptaków występujących w agroekosystemach zanik „śródpolnych populacji” sroki spowodowany jest
najprawdopodobniej zmianami w jakości środowiska, w tym zanikiem bazy pokarmowej, w
wyniku intensyfikacji produkcji rolniczej. W świetle wyników uzyskanych w krajobrazie rolniczym okolic Wrocławia i innych rejonach Polski, można spodziewać się dalszego wycofywania się sroki z terenów pól uprawnych. Sroka jednak, w przeciwieństwie do innych
ptaków związanych z agroekosystemami, nie jest gatunkiem potencjalnie zagrożonym, zważywszy na jej liczne występowanie na obszarach zurbanizowanych i postępujący wzrost liczebności w tym środowisku.
SŁOWA KLUCZOWE: sroka, Pica pica, miejsca gniazdowe, krajobraz rolniczy, intensyfikacja
rolnictwa
Introduction
There has been a considerable increase in the numbers of magpies Pica pica across
Europe since the end of the second world war (Birkhead 1991, Jerzak 2001). Data
from Western Europe and Poland indicate at an increase in magpie populations in
the urban areas, concurrent with a decrease within agroecosystems (Gregory &
Marchant 1995, Dombrowski 1997, Górski 1997, Siriwardena et al. 1998).
In Poland the abundance of the magpie population in urban areas, mainly
towns, has been well documented (Jerzak 2001, Tomiałojć & Stawarczyk 2003). In
spite of the large number of quantitative data from farmland of Poland (review by
Dombrowski 1997), there has been a lack of long-term studies on changes in the
numbers of that species in such areas. In the period of intensive transformations in
farming systems in Poland, it seems necessary to determine the present state of
natural resources, including the bird fauna of farmland areas, and to monitoring
the ongoing qualitative and quantitative changes in their structure.
The aim of this work was to determine the abundance of the magpie population and characterize its nesting sites (used tree species, height of nest sites) in a
fragment of the Wrocław Plain under the intensive of agricultural practises.
Magpie Pica pica nest sites in farmland in vicinity of Wrocław city (SW Poland)
511
Study area and methods
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The study area (57.5 km ) is situated within two mezoregions of Primordial Valley of the Odra and Wrocław Plain, which belong to a greater physiographic unit of
Silesian Lowland (Kondracki 1988). The predominant land use was arable land,
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which occupied about 91% of the area (52.32 km ). This area was characterized by
the lowest share of forests and woodlots in Poland, which amounted to 1.3%. The
26 villages surveyed occupy an area of 4.56 km2 (7.9% of all surveyed area). Their
area ranged from 0.005 to 1.01 km2 (average ± SD = 0.19 ± 0.23 km2). Owing to
the good and very good quality of the soil, most of the area is under intensive farming. Commodity farms prevail, at times exceeding 100 ha, especially in the western
and southern parts of the study area. Medium size, farms of a few hectare remained
mostly around the villages. In the year 2000, the largest crop area was wheat
(50%), rape (25%), root crops (10%) and maize (8%).
The location of Magpie nests (including species of nesting tree and height of
nest) was recorded in the winter of 2001/2002. Nests were counted as originating
from the last breeding season (2001), if a “roof ” or its remnants could be seen.
Searching for occupied nests, conducted on part of the area (15.8 km2 – see Fig. 1)
in the consecutive breeding season (2002), indicated that the number of nests occupied was the same (n = 5) as in winter season. This may indicate that the number of nests spotted in winter season corresponds to actual number of breeding
pairs. According to Fassola and Brichetti (1983), data on the numbers of magpie
nests collected in winter time after a breeding season can be by 5% lower than actually existing. However, in that period it is markedly easier to spot the nests in
trees devoid of leaves (Górski 1989).
Results
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A total of 56 nests was located (density – 0.97 pairs/km ), including 46 nests
(82%) located in village (settlements) areas (Fig. 1). The remaining 10 (18%)
nests were found outside built-up areas. Magpie nests were found in 24 (92%) of
the 26 surveyed settlements. The difference in the number of nests located in
built-up areas and open spaces was statistically significant (c2 = 46.29; df = 1, p <
0.001). A positive, statistically significant correlation was found between village
area and the number of nests located in its precincts (rs = 0.66, p < 0.001, n = 26).
The mean density of nests in built-up areas was 53 times higher that in agricultural
areas (10.1 pairs/km2 – villages vs. 0.19 pairs/km2 – farmland). Density in particular
settlements ranged from 0 to 200 pairs/km2 (for 26 villages the mean ± SD was
33.7 ± 61.6 pairs/km2). A negative statistically significant correlation was found
between village area and density of nests localized in its precincts (rs = –0.67, p <
0.001, n = 26).
Nests were located on 14 tree and 2 bush species (Table 1). Nearly 22% of the
nests were located in poplar trees Populus spp. (hybrids of poplars). Nests in villages were located at the height of 5 to 20 meters, and most of them (n = 32, 70%)
were over 10 meters high. Outside built-up areas, the height was 3 to 12 meters,
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Grzegorz Orłowski
and 70% of them (n = 7) were built below 5 meters. The mean height of nests in
village areas was nearly twice that in open farmland (mean ± SD = 11.1 ± 3.7 m in
villages vs. 5.7 ± 2.9 m in open areas). This difference was statistically significant
(Mann-Whitney test, U = 52.50, Z = 3.80, p < 0.001). Nests in open land were at a
distance of 200 to 850 meters from the nearest buildings, the average (± SD) distance being 382 (± 198) m.
Fig. 1. Distribution of magpie nests (N=56) in agricultural landscape of the Wrocław Plain.
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Thick grey line indicates borders of the area (15.8 km ) studied from 1977–79 by Ławniczak
(1980)
Ryc. 1. Rozmieszczenie gniazd sroki (N=56) w krajobrazie rolniczym Równiny Wrocław2
skiej. Grubą szarą linią zaznaczono granicę powierzchni (15,8 km ) badanej w latach
1977–79 przez Ławniczak (1980)
Magpie Pica pica nest sites in farmland in vicinity of Wrocław city (SW Poland)
513
Table 1. Nest-tree species in agricultural landscape of Wrocław Plain
Tabela 1. Drzewa gniazdowe sroki w krajobrazie rolniczym Równiny Wrocławskiej
Tree species/Gatunek drzewa
Number of nests/Liczba gniazd Percentage/Udział (%)
Poplar Populus sp.*
12
21.5
Small-leaved lime Tilia cordata
7
12.5
Common ash Fraxinus excelsior
7
12.5
Pedunculate oak Quercus robur
4
7.1
European alder Alnus glutinosa
4
7.1
Black locust Robinia pseudacacia
4
7.1
Silver birch Betula pendula
3
5.3
Crack willow Salix fragilis
3
5.3
Lombardy poplar Populus nigra ‘Italica’
2
3.6
3.6
European white elm Ulmus laevis
2
London plane tree Platanus x acerifolia
2
3.6
Apple Malus sp.
1
1.8
European plum Prunus domestica
1
1.8
Mulberry Morus alba
1
1.8
Grey willow Salix cinerea
1
1.8
Blackthorn Prunus spinosa
1
1.8
Unidentified fruit trees
Total/Razem
1
56
1.8
100
*Hybrids of the native black poplar Populus nigra with north-american species
*Hybrydy rodzimej topoli czarnej Populus nigra z gatunkami północnoamerykańskimi
Discussion and conclusions
The data obtained indicated that in the Wrocław Plain, the magpie population is
mainly found in village areas. In western Europe (Scotland, Denmark, Germany,
Great Britain) in the sixties and eighties in agricultural areas from 40 to 100% of
the nests was located in settlements (compiled by Jerzak 1988). Also in the
Lubusian Region (NW Poland) the share of nests located in villages was from
76–90% (Jerzak 1988).
The total density of magpie nests in the Wrocław Plain, was in the range recorded from other Polish agricultural areas (i.e. from 0.2 to 1.4 pairs/km2)
(Dombrowski 1997). A marginally higher density (1.5 pairs/km2) was found in
1994 on cultivated fields (6.7 km2) situated in the outskirts of Wrocław (Orłowski
et al. 2002).
On six plots in the farming landscapes around the town of Koszalin there was a
large differences in density between village areas and the open agricultural landscape (density from 4.7 to 29.6 pairs/km2), similar to that recorded in the Wrocław
Plain. In one of the plots the density was found to be 129 times higher in the village
area than in the neighbouring agricultural fields (Górski 1997). The overall density
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Grzegorz Orłowski
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in village areas of Wrocław Plain (10.1 pairs/km ) is close to results given for urban
areas in Poland (compiled by Orłowski et al. 2002). In 1994 in the urban area of
south-west part of Wrocław (19.46 km2) the density was found to be 12.6
pairs/km2 (Orłowski et al. 2002).
In the agricultural landscape of the Wrocław Plain, like in urban areas in Poland
(Jerzak 1997) the largest percentage of nests was situated on poplar hybrids Populus
spp. (21.5% – Wrocław Plain vs. 31% – Poland) which are characterized by broadly
spreading crowns. Also in the south-western part of Wrocław poplar hybrids were
the most favoured nesting tree (34.5%) (Orłowski et al. 2002). Up to the present,
mid-field magpie populations tended to nest in tussocks of blackthorn and hawthorn
along country roads and field margins (Ptaszyk 2000). In spite of the presence of
such biotopes in the area studied, only one nest was found in blackthorn.
In the Wrocław Plain the mean height of nest sites in villages was close to that
reported by Jerzak (1988) for that environment in Poland (12.3 m – Poland vs. 11.1
– Wrocław Plain). However, in the Wrocław Plain the nests were built slightly
higher outside built-up areas compared with data for the rest of Poland (5.7 –
Wrocław Plain vs. 4.1 – Poland). This also influenced the lack of nests in low
bushes (blackthorn, hawthorn, bushy willows). Outside town areas as many as
64.1% nests were situated 2.6–2.7 m above the ground, on low willows Salix spp.
and blackthorn bushes (Jerzak 1988).
Compared to the data from 1977–79 originating from an area of 15.8 km2
(Ławniczak 1980) situated in the middle of the area studied (Fig. 1), a 2–3-fold decrease in the magpie population was recorded. In the seventies 17.5, 10 and 14.5
magpie pairs breed there, successively; and in winter of 2001/2002 there were 5
nests (this represented a 2–3-fold decrease in density, from 0.63–1.07 to 0.32
prs/km2 in the respective period). During this period the density remained stable
at the former level in villages (Smardzów and Łukaszowice – Fig. 1).
In western Europe a decrease in magpie populations within agricultural fields
has been observed since the 1960s (Cooke 1979, Gregory and Marchant 1995).
In the light of the results obtained, and in view of the intensification of agricultural production, one can expect a further withdraw of the magpie from farmland.
Most probably that process will further extend to eastern Europe. The magpie, however, contrary to other farmland birds is not a potentially endangered species, as its
populations are abundant in urban areas and on the increase in that environment.
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