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Digitale Literatur/Digital Literature

Zeitschrift/Journal: Ornithologischer Anzeiger

Jahr/Year: 2000

Band/Volume: 39_2-3

Autor(en)/Author(s): Vogrin Milan, Vogrin Nusa

Artikel/Article: Mute Swan Cygnus olor in 227-230 V o g r in & V o g r i n : Mute© Ornithologische Swan Cygnus Gesellschaft olor Bayern, in Slovenia download unter www.biologiezentrum.at 227

Orn. Anz. 39: 227-230

Mute Swan Cygnus olor in Slovenia

Milan Vogrin & Nusa Vogrin

Zusammenfassung

Es wird ein Überblick über den Status des Höckerschwans in Slowenien gegeben. Die erste Freibrut fand 1982 im Norden statt. Zur Zeit beträgt der Brutbestand ca. 50 Paare, davon die Hälfte entlang der Drau. Zwischen 400 und 700 Vögel überwintern in Slowenien, die Mehrzahl im nordöstlichen Landesteil.

Introduction

M u te S w a n Cygnus olor is a com m on bree­ increased and was recently estimated at ding species in north-western Europe, about 45 000 individuals (D e l a n y e t al. whereas during winter Mute Swans may 1 9 9 9 ). migrate south to Central and Southern In Slovenia Cygnus olor is a less studied Europe (e.g. B e a m a n & M a d g e 1 9 9 8 , W ie ­ species with only a few published papers l o c h et al. 1998). In the last thirty years the (e.g. B r a c k o 1 9 9 6 , H u d o k l in 1 9 9 6 ). Accor- breeding population of Mute Swans ding to W ie l o c h ( 1 9 9 1 ), Slovenian bree­ increased and expanded to the south and ding swans belong to the so-called south- east (e.g. W ie l o c h 1984, 1991). The win- east European or west Ukrainian-Hunga- tering population in the East M editerrane- rian group. an and in the region also

Breeding

According to the Atlas of Slovene bree­ olor in the wild comes from the Dravograd ding birds (G e is t e r 1 9 9 5 ) , the Mute Swan reservoir along the river , near the is distributed mainly in north-eastern border with Austria, from 1 9 8 2 (V r e S & Slovenia along the river Drava. The bree­ V r h o v n ik 1 9 8 4 ) . From this year on bree­ ding population was estimated in 1 9 9 5 at ding occurred regularly in the north-east 3 0 - 5 0 pairs, the recent one at 5 0 breeding and the population increased to about 22 pairs (pers. obs.). One of the most im­ pairs (B r a c k o 1 9 9 6 ) . Before this confir­ portant reasons for the increase of the med breeding only nesting of so-called breeding population in Slovenia were new park swans was known. Today most birds reservoirs on rivers and gravel pits along breed on reservoirs along Drava river, the rivers, feeding of the birds by people and rest nests also on gravel-pits and on fish­ eutrophication of water (higher producti- ponds situated along rivers Drava and vity). Mura. The first confirmed breeding of Cygnus Very probably many birds breeding in 228 © Ornithologische Gesellschaft Bayern, download unter www.biologiezentrum.at Orn. Anz. 39, 2000

Slovenia are descendants of naturalised (north-western Slovenia) (Ja n & S l iv n ik birds and, to a minor degree, birds from 1996) and at river near Otocec (south- north-eastern countries. The first swans eastern Slovenia) around 1970 (H u d o k l in were released in 1902 at the Lake 1996).

W inter

Wintering data mainly come form surveys About 15 years ago, wintering on river which were carried out in mid January as Drava was only about 10-30 % of todays part of the International Waterbird Cen- numbers (pers. obs.). Numbers of win­ sus. General surveys were presented by tering Mute Swan on river Drava increased St u m b e r g e r (1997,1998,1999) and G e is t e r also in the last years as elsewhere in Euro- (1997). pe (D e l a n y et al. 1999). During mid-win- Winter distribution of Mute Swan is very ter the proportion of young in north-ea- similar to summer distribution (S o v in c stern Slovenia was about 20-40 % (pers. 1994). Mute Swans were found almost obs.). On the Krka river H u d o k l in (1996) exclusively on big rivers, except during found that the proportion of young throu- autumn and spring migration when swans ghout the year was between 3 (winter) and were recorded also on various standing 29 % (spring). water s. Peak numbers of Mute Swans oc- Numbers of wintering swans on river curred between December and January. In Drava in last years are close to 1 % thres- February followed a slow reduction (ac- holds for East Mediterranean / Black Sea cording to author’s estimation by 10 %) (450 birds) where Slovenia belongs to, and in March a strong reduction. becoming an area of international im- In the last years wintering Mute Swans portance for wintering Mute Swans (D e l a ­ in Slovenia numbered between 400 and n y et al. 1999). 700 (Table 1). The maximum total winter First data about wintering on the coast count in Slovenia reached 725 birds in come from 1993 (S k o r n ik 1996) where 8 January 1999. The majority of birds were birds were present. However, from 1997 recorded in the north-east, first of all on Mute Swans were not present during mid- river Drava and their reservoirs, where winter counts. more than half of the Slovenian wintering Birds tend to be gregarious in winter. population was recorded (Table 1). The largest flocks with up to 200 birds were found on the reservoir Ptuj (pers. Table 1: Numbers of wintering Mute Swan obs.). Here they benefit from food provi- Cygnus olor in Slovenia. Data from national sioned by the public. mid-winter waterfowl counts. - Zahlen über­ Observed ringed swans indicate that winternder Höckerschwäne in Slowenien. Mute Swans which winter in Slovenia are those which breed in Slovenia as well as Year River Drava Whole country birds from north-eastern Europe (e.g. 1996 110 206 Austria, Slovakia, Hungary, Poland) (S e r e 1997 202 397 1996, pers. obs.). From observations of 1998 245 389 ringed swans in larger flocks during win­ 1999 408 725 ter I estimate that about 5-10 % of swans V o g r in «Sc V o g r i n : Mute© Ornithologische Swan Cygnus Gesellschaft olor Bayern, in Slovenia download unter www.biologiezentrum.at 229

were ringed in foreign countries (see abo- year with him was also a mate and young. ve). “Polish Swan” Cygnus olor “immutabi- According to some ringed birds winter- lis” a domesticated form also occurs in ing in the same area for many years, it Slovenia. According to W ie l o c h & C z a p u - seems that Mute Swans have strong win­ l a k (1991) this form in Europe occurs in ter site fidelity. For example an adult male rates from 2-100 %. The rate of this form which was ringed in 1993 in Austria (AA among breeding swans is not known, while 1058) was observed on Vrbje pond in Low­ during winter in the last years about 20- er valley each year from 1994-1999 30 % of adult birds belong to the immuta- (V o g r in 1996, pers. obs.). Moreover, every bilis form (pers. obs.).

Threat

Relatively few Mute Swans were found swan, though this is thought to be rare dead (see also G eister 1997). M ost of these (Ja n «Sc S l iv n ik 1996, pers. obs.). Moreover, birds die as a direct result of vandalism, we must take into account also lead poi- shooting and predation. The M ute Swan is soning which is mostly neglected. Inge- protected by law but a few are still shot by sted lead affects the neuromuscular sy- vandals. Vandalism of nests or young also stem of the swans (and other waterfowl) occurs (e.g. VreS & Vrhovnik 1984, B r a k - and inhibits the normal functioning of the k o 1996, J a n «Sc S liv n ik 1996, pers. obs.). gizzard. In some areas lead poisoning was The species has a few natural predators in responsible for more then 50 % of deaths Slovenia. Only domestic dog and fox Vul- of swans (K ir b y et al 1994). pes vulpes are capable of taking an adult

Acknowledgements

We thank Dr. M. Wieloch for additional literature and T. Mischler for checking the manuscript.

Abstract

An overview of the status of the Mute Swan breeding pairs are present in the country, about Cygnus olor in Slovenia is presented. First bree­ half of them along river Drava. During the ding in the wild took place in 1982 in the winter between 400 and 700 birds stay in Slove­ northern part of the country. Today about 50 nia, mainly in the north-eastern part.

Literature

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Milan Vogrin* & Nusa Vogrin Zg. Hajdina 83c, SI-2288 Slovenia E-mail: [email protected] * corresponding author