Berkut. Vol. 8. Is. 2. 1999. P. 150-154.

 

 

The impact of landscape structure

on occurrence of White Stork’s nests

 

C. Latus, K. Kujawa

Влияние структуры ландшафта на встречаемость гнезд белого аиста. - К. Латус, К. Куява. - Беркут. 8 (2). 1999. -  Целью работы было определение показателей структуры ландшафта, влияющие на встре­ча­емость гнезд белого аиста. Исследования проведены на участке в 660 км2 в Восточной Германии (долина р. Одер), где плотность гнездования достигает 4 пар на 100 км2. Предпочтение местообитаний белым аистом определялось путем исследования структуры ландшафта в радиусе 1 км от гнезда. В населенных пунктах было случайным образом выбрано 56 “гнездовых участков” и 34 “контрольных участка” (без гнезд). Структура ландшафта (соотношение местообитаний, индекс разнообразия Шеннона H', плотность границ и т. д.) измерялись по аэрофотоснимкам (1:10000). “Гнездовые участки” характеризовались более высокой долей травянистых биотопов и водоемов и большим значением H': 1,37 по сравнению с 0,95 на “контрольных участ­ках” (P < 0,01). Аисты явно предпочитали более разнообразные местообитания – 80 % “гнездовых участков” имели высокую степень разнообразия (0,81-1,70), в то время как 80 % “контрольных участков” в намного более низком классе разнообразия (0,21-0,80). Травянистые биотопы также имели значительное влияние. Аисты предпочитали для гнездования прилегающие и умеренно фрагментированные участки.

 

Abstract. The objective of the study was to determine the landscape structure indices influencing the occurrence of  White Stork’s (Ciconia ciconia) nests. The analyses were performed for the MOL-district (660 km2) in East Ger­many (Oder valley) where the density of breeding pairs as high as to 4 per 100 km2. White Stork habitat preferences were determined by investigating landscape structure within a 1 km radius of nesting locations, ‘breeding sites’ (N = 56), within  and for ‘control sites’ (N = 34), randomly selected points  in the villages without stork’s nests. The land­scape structure (habitat proportions, Shannon’s diversity index H’, density of edges, etc.) was measured by evaluating aerial photographs (1:10000). Breeding sites were characterised by a higher proportion of grasslands and inshore waters as well as by a significantly higher (P < 0,01) value of H’ 1,37 compared to 0,95 for ‘control sites’. Storks clearly preferred more differentiated landscapes – 80 % of ‘breeding sites’ were localised in very high diversity classes (0,81-1,70), while 80 % of ‘control sites’ were in much lower diversity classes (0,21-0,80). Also grasslands were found to have a strong influence. Storks preferred contiguous and moderately fragmented grasslands as nesting habitats.

 Key words: White Stork, East Germany, habitat preference, landscape structure.

Address: Claudia Latus, ZALF, Institute of  land-use systems and landscape ecology, Eberswalderstr. 84, 15374 Müncheberg, Germany. e-mail: clatus@zalf.de.

Krzysztof Kujawa, Research Center for Agricultural and Forest Environment, Polish Academy of Sciences, Field Station, Szkolna 4, 64-003 Turew, Poland. e-mail: ortolan@priv7.onet.pl.

 

 

Introduction

 

Intensive land-use management affects  the structural arrangement of agricultural land­scapes and influences the occurrence of species leading to change or serious loss of bio­diversity (Mc Laughlin, Mineau 1995). Additional information is needed concerning abiotic (physical and chemical) landscape features and connections between landscape and the biota  to help forecast ecological threats and support efforts to protect biodiversity. The White Stork (Ciconia ciconia) was selected for an investigation of the integration of a species into a landscape due to its large area-habitat preferences and ability to adapt to farmland. The objective of our study was to determine the landscape parameters strongly associated with  the occurrence of White Stork’s nests and, therefore those which should be considered as essential for effective protection of the species.

 

Study area

 

The study was carried out on a 660 km2  area in the district MOL (Brandenburg), located in the Oder river valley. In the 1990s, the density of White Stork reached as high as  4 pairs/100 km2 (Mitteilungsblatt..., 1995). The district MOL has a typical land use composition for agricultural regions: agricultural use (62 % ) (92 % crop fields and 7 % grasslands), woodlands (24 %), inshore waters (3 %), settlements (9 %) and other land uses (2 %) (LDS Bran­den­burg, 1995). Fifty-one percent of the crop fields is used for grain. The land is intensively cultivated: the annual applications of NPK reach 200 kg per ha, the wheat yield is 45-55 dt/ha and  pesticides are sprayed from 2-6 times/year (Amt für Landwirtschaft, 1995). The district MOL has 82 inhabitants/km2. The density of human settlement is 6/100 km2. The annual mean precipitation is approx. 500 mm; the mean temperature is  +18 °C in July and  –1 °C in January (LDS Brandenburg, 1995).

 

Methods

 

The landscape structure in the proximity of nests occupied by breeding pairs within last five years (“breeding sites”: BS, N = 56)  was compared to the landscape structure of areas without White Stork’s nests (“control sites”: CS, N = 34). Because nearly all of the  nests are localised in the settlements (Ranner, Tie­fen­bach 1994), CS were taken as randomly se­lected points in settlements without  White Stork’s nests, close to the border of the settlements. The landscape structure was investigated within a 1 km  radius around BS and CS, based on a finding by Creutz (1988) who noticed that during the earliest stage of fledgling development their parents need view-contact with the nests. The landscape structure was measured with the aid of black and white aerial photographs at a 1:10 000 sale. The measurements were focused on the patches and boundaries between patches. A “patch” was defined as a homogeneous area of land (according to photograph sensitivity) and classified according to six land-use classes: woodlands, crop fields, grasslands, inshore waters (seas, ponds etc.), bushes (cemeteries, gardens etc.), settlements.

The chosen variables can be split into three groups:

1. Variables based on the main land-use classes  proportions: a) the percentages of crop fields, woodlands, grasslands, inshore waters, bushes, settlements, b) landscape diversity in­dex defined as Shannon’s diversity index , in which is the proportion of i-th habitat and c) the openness of a landscape. The openness of landscape is a good indicator for birds to determine a free view of the nest surroundings to recognise possible feeding areas as well as dangers. We defined an open land as covered by crop fields and/or grasslands (Andries, 1984), thus the open­ness of landscape is the percentage of open land.

2. Variables based on the linear structures: the densities of different types of boundaries (between crops and grasslands, woodlands and grasslands, etc.) as well as their total.

3. Variables based on the distances: a) the distance from BS (CS) to the nearest patch determined separately for all land-use classes, b) the distance between the same type of land-use patches.

 

Results

 

Impact of  land-use types composition

The land-use of the area at BS and CS differed markedly. BS’s area was charac­terised by a smaller percentage of crop fields (52 % and 71 %, respectively), and much higher percentage of grasslands (11 % and 4 %) as well as inshore waters (6 % and 1 %). According to Chi-square test the differences are statistically significant at P<0,001 (Fig. 1). The difference in land­scape diversity between BS and CS (1,37 and  0,95, respectively) is statistically significant at P<0,01 (Poole, 1979). In addition, the difference in the frequency distribution between BS and CS in relation to the  H’ index is statistically signi­fi­cant (cc2 test, P<0,001). Eighty percent of BS were localised in high diversity clas­ses of 0,8-1,7 while 80 % of CS were found in lower diversity classes of 0,2-0,8.

 

 

Fig. 1. Land-use of the area around breeding sites (BS) and control sites (CS).

Рис. 1. Использование земель вокруг гнездовых (BS) и контрольных (CS) участков.

 

Special consideration was given to some types of land-uses important for White Storks for nesting and feeding purposes. Crop fields and grasslands may be regarded as potential feeding areas but woodlands as a possible indicator for disturbance. The frequency distributions of BS and CS varied (cc2 test, P<0,001) in relation to crop field coverage (Fig. 2a) as well as to grassland percentage (Fig. 2b). Sixty percent of BS were localised in places characterised by crop fields covering areas in a range of 20-60 %, while up to 80 % of CS were surrounded by areas covered by 60-100  % of crop fields. Seventy-five percent of BS were found in the places where grasslands cover  from 5 % to more than 30 % of the land surface, while about 85 % of CS were found in areas with a very low percentage (0-10 %) of grasslands. These results correspond with the grassland/open land rate analyses which showed a significantly higher value of the rate  (U-test, P<0,001) for BS. Regarding woodlands, 80 % of BS were found in the areas with 0-20 % woodland coverage,  while 60 % of CS were surrounded by 10 % to more than 30 % woodland coverage (Fig. 2c). The differences are statistically significant (cc2 test, P < 0,001).

 

a)

 

b)

 

c)

 

Fig. 2. Frequency distribution of breeding sites and control sites.

Рис. 2. Частотное распределение гнездовых и контрольных участков:

a) – в зависимости от площади полей;

b) – в зависимости от площади лугов;

c) – в зависимости от площади лесов.

 

Impact of boundaries

BS were more frequently localised in the range of 12,1-24 km of all boundaries per circle while CS were found to be markedly most frequent in the range of  12,1-16 km per circle (Fig. 3). The difference reported here is statistically significant (cc2 test, P < 0,01). Special attention was focused on the fragmentation of grasslands the main feeding areas for White Stork. Nests were found more frequently in the areas characterised by significantly higher density of grassland boundaries (cc2 test, P < 0,001) (Fig. 3).

 

Fig. 3. Frequency distribution of BS (thick line) and CS (thin line) in relation to density of boundaries (in km/circle).

Рис. 3. Частотное распределение гнездовых (толстая линия) и контрольных (тонкая линия) участков в зависимости от плотности границ (в км на круг).

 

Discussion

 

Most studies on the distribution of White Stork’s nest were based on singular habitat ana­lyses, for example on the influence of  grass­­land percentage on the density of breeding pairs (Thomsen, 1995, Schneider, 1988). The re­sults reported here show much more compli­cated relationships between the species and pre­ferred habitat and support previous findings that investigations of the species must be carried out in landscape contexts as other authors have already noticed (Flather, Sauer 1996).

The main factors responsible for survival of a given species are the possibility for nest building and sufficient food supply for its brood. The importance of food supply for White Stork in his breeding region was showed e. g. by Pinowska et al. (1989) and the influence of food supply on breeding success has been analysed by Löhmer et al. (1980), Profus (1986), Struwe and Thomsen (1991). Although results are based on the ana­lysis of landscape structure characteristics, clear preferences for special landscape features outside of the one km radius can be easi­ly recognised. The landscape structure around BS and CS differed depending on the percentages of crop fields, grasslands and woodlands as well as on the diversity of landscape. Indeed­ variables based on distances are of less impor­tance within 1 km around nest, but variables based on linear structures are  significant different and provide more comprehensive infor­mation about the degree of landscape frag­men­tation determined by the density of bound­a­ries. These preferences are surely linked with the feeding biology of White Stork. The species is a generalist in food intake. As Lakeberg (1995) described, this species changes its food during the breeding season from earthworms and amphibians in the first phase to small mam­mals preferred later during breeding older fledg­lings, probably because of a higher energy content (Profus, 1986). But decisive role for White Stork is played not by the potential food supply by itself, but food availability (Alon­so et al.,1991). The species as a stepper bird with quick sight reacts on small moving animals (Creutz, 1988). White Stork looks for mice and other animals in open land, espe­ci­al­ly with low vegetation, harvested crop fields and grasslands, which can be found much mo­re easily (and on the average closer to the nest) in diversified landscape compared to unified one. So, it seems that diversified, mosaic-like landscapes consisting of many patches of different land-use types (incl. small woods, small water bodies etc.) but with some minimum area of grasslands (10-20 %) as main feeding area and moderate density of all boundaries as well as boundaries of grassland patches are an optimal breeding habitat for White Stork in intensively used farmland in Europe.

Acknowledgement: The investigation was executed in co-operation between ZALF, Institute of Land-use Systems and Landscape Ecology in Germany and RCAFE PAS in Poland supported by BML (Project No. 84). Many thanks for the data on White Stork  to N. Wenzel, W. Trebesch and W. Schmidt from NABU, Germany as well as to M. Röhl for technical help.

 

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