Zadrževalnik Medvedce v mreži evropskih mokrisč - danes in jutri
Medvedce reservoir in the network of European wetlands -today and tomorrow
V	dosedanjih treh desetletjih izhajanja glasila Acrocephalus je izšlo devet tematskih številk (neupoštevajo~ dveh bibliografskih številk), od katerih je {est prakti~no v celoti posve~enih mokriš~em. To spri~o velikega ornitološkega in naravovarstvenega pomena mokriš~ ni presenetljivo. Podatki iz Evrope namre~ pravijo, da so ptice kontinentalnih mokriš~ danes med najbolj ogroženimi ekološkimi skupinami ptic, saj jih po številu vrst z nazadujo~imi populacijami prekaša le kmetijska krajina (BirdLife International 2004). O~itno smo se slovenski ornitologi tega dejstva za~eli zavedati zelo kmalu. Tako smo v inventar Mednarodno pomembnih obmo~ij (IBA) do leta 2004 uvrstili najpomembnejše nižinske reke, poplavne ravnice in gozdove ter obalna mokriš~a (Polak 2000, Božič 2003) - skupaj kar 12 obmo~ij, ki jih vsaj delno v najširšem pomenu besede lahko obravnavamo kot mokriš~a. Vendar pa so le na treh, morda štirih obmo~jih (obe obalni mokriš~i in reka Drava, pogojno presihajo~e Cerkniško jezero) dejansko v ospredju vodne ptice, kot jih definira Wetlands International (glej Delany & Scott 2006) in jih ve~inoma razumemo tudi mi. Kosca Crex crex, travniško ptico, ki v celotnem življenjskem ciklu naseljuje veliko bolj suhe habitate kot ve~ina drugih predstavnikov družine tukalic Rallidae (SchAffer & Koffijberg 2004), v tem kontekstu težko uvrstimo med vodne ptice.
V	minulem desetletju sistemati~no zbrani podatki na zadrževalniku Medvedce in okolici pa so nas privedli do to~ke, ko smo spoznali, da premoremo še eno mokriš~e izjemnega mednarodnega in nacionalnega pomena za vodne ptice. In to takšnega tipa, kot je pravzaprav najve~ mokriš~, vklju~enih med obmo~ja IBA v Evropi — celinsko, stoje~e vodno telo (57% vseh obmo~ij IBA, opredeljenih kot mokriš~a; Heath & Evans 2000). Pomemben del tega tipa mokriš~ so v današnjem ~asu ribniki, torej vrsta rabe, ki se je v zadnjih letih opravljala tudi na zadrževalniku in je pravzaprav odgovorna za nastanek vodnega telesa znotraj visokovodnega nasipa, v obliki, kot jo poznamo danes. Polnaravni, ekstenzivno upravljani ribniki so zna~ilni za Srednjo in Vzhodno Evropo (Petkov 2006), tudi Slovenijo, kjer pa ne premoremo takšnih ogromnih ribogojskih kompleksov, kot jih imajo na primer na Hrvaškem, Madžarskem in v Srbiji (glej LovAszi 2002, Radovic et al. 2005, Heath & Evans 2000). Kljub temu pa so varstveno najpomembnejše gnezdilke na zadrževalniku Medvedce podobne kot na teh obmo~jih. Med temi velja posebej omeniti kostanjevko Aythya nyroca, vrsto globalne varstvene pozornosti, ki je zna~ilna gnezdilka plitvih in zaraš~enih celinskih stoje~ih voda s težiš~em populacije v JV Evropi. Kostanjevka je v Sloveniji donedavna veljala za neredno gnezdilko, vendar se je v zadnjih letih izkazalo, da na zadrževalniku redno gnezdi, število gnezde~ih parov pa se je v letu 2009 povzpelo na 12. Zadrževalnik je s tem trenutno skrajna SZ to~ka bolj ali manj zveznega gnezditvenega areala kostanjevke v tem delu Evrope. Ob sedanjem trendu je pri~akovati, da bo populacija na zadrževalniku v nekaj letih dosegla kriterij za globalno pomembno obmo~je te ptice (20 parov).
Ce lahko pomen zadrževalnika za gnezdilke nedvomno pokažemo, pa to kljub odli~nim kvantitativnim ornitološkim podatkom, predstavljenim v pri~ujo~i
številki glasila, težko naredimo za vrste, ki se čez območje le selijo. Tukaj moramo takoj povedati, da se po teh podatkih tu ne pojavlja več kot 1% biogeografske populacije nobene vrste, kar je eden izmed kriterijev za opredelitev območja IBA za negnezdeče vrste. Morda nam bo s celodnevnimi štetji v času selitve to v prihodnjih letih uspelo potrditi za pribo Vanellus vanellus, ali pa bo ta kriterij navsezadnje dosegla velika bela čaplja Casmerodius albus katere številčnost se še vedno povečuje. Ob tem ni nepomembno dobro znano dejstvo, da tako majhna območja, kakršno je zadrževalnik Medvedce z okolico, omenjene kriterije, ki so za večino vrst zelo visoki, v praksi težko dosegajo. Kaj pa druge vrste? Za primer vzemimo močvirskega martinca Tringa glareola. Vrsta gnezdi večinoma v Severni Evropi in se seli v širokem pasu čez celoten kontinent, kjer se ustavlja predvsem na kontinentalnih mokriščih. Redko se združuje v večje jate, zato je v Evropi zunaj območja gnezdenja znano le eno samo območje, kjer se pojavlja 1% biogeografske populacije (10 500 os.) (Delany et al. 2009). Jasno je, da koncept varstva, skoncentriran na razmeroma majhno število najpomembnejših območij, pri tej vrsti povsem odpove. Nedavno objavljena raziskava z majhnega umetnega mokrišča v Avstriji je s pomočjo individualnega označevanja pokazala, da so postanki močvirskih martincev na spomladanski selitvi zelo kratki. Število sočasno pojavljajočih se osebkov na območju je bilo majhno, turn-over pa velik. Poleg tega je za močvirskega martinca značilna strategija selitve s t.i. poskakovanjem (angl. »hopping«), pri kateri seleče se ptice na mah preletijo le kratke razdalje s številnimi vmesnimi postanki. Sporočilo je, da je za takšne vrste ohranjanje goste mreže mokrišč, četudi majhnih, vzdolž selitvene poti ključnega pomena za njihovo ohranitev (Muraoka et al. 2009). Podobnih vrst je gotovo še veliko, mokrišč pa v Srednji Evropi žal ne več, saj so bila številna uničena v preteklih desetletjih. Enako lahko rečemo tudi za širšo okolico zadrževalnika Medvedce oziroma Dravsko in Ptujsko polje. Tudi zato je zadrževalnik Medvedce tako zelo pomemben.
BirdLife International je leta 2008 zadrževalnik Medvedce z okolico pod imenom »Crete« uvrstil med Mednarodno pomembna območja za ptice (IBA). S tem je tudi pripravljena podlaga za razglasitev Posebnega območja varstva (SPA) po Direktivi EU o pticah (79/409/EGS) in uvrstitev med območja Natura 2000, na katero še čakamo. Ze leta 2006 se je na Biogeografskem seminarju za celinsko regijo izkazalo, da bi moral biti zadrževalnik Medvedce razglašen tudi kot potencialno posebno ohranitveno območje (pSCI) za habitatne tipe (Zagmajster & Skaberne 2006), ki so pomembni tudi za ptice. Tudi to do danes še ni bilo narejeno, čeprav je vzpostavitev ustreznih oblik institucionalnega varstva nadvse potreben prvi korak pri ohranjanju območja. Na zadrževalniku in bližnji okolici so v zadnjih letih tako po obsegu kot intenzivnosti v porastu številni dejavniki ogrožanja. Slišati je bilo tudi različne pobude, ki bi v primeru realizacije povsem spremenile značilnosti območja in drastično povečale obseg motenj. Cas za ukrepe za dolgoročno ohranitev tega enkratnega območja je zdaj, saj je že jutri lahko prepozno! Ta tematska številka našega glasila, v celoti posvečena zadrževalniku Medvedce in okolici, ima torej širši pomen. Namenjena je tudi vsem upravljavcem in aktivnim uporabnikom tega prostora ter tistim, ki o tem odločajo — lovcem, ribogojcem, gozdarjem, občinam, državnim naravovarstvenim službam itd. Brez njihovega sodelovanja ga bomo izgubili za vedno.
In the last three decades, nine thematic numbers of the journal Acrocephalus (excluding two bibliographical numbers) have been published, six of which have been more or less fully dedicated to wetlands. Owing to the great ornithological and conservation significance of these wet habitats, this is not at all surprising, for the data coming from Europe tell us that birds of continental wetlands are currently among the most endangered ecological groups of birds, given that, in terms of the number of species with declining populations, they are surpassed only by agricultural landscapes (BirdLife International 2004). It is obvious that we, Slovenian ornithologists, became aware of this fact fairly early. Prior to 2004, we managed to include into the IBA inventory our most important lowland rivers, floodplains, riverine forests and coastal wetlands (Polak 2000, BoŽIČ 2003) -altogether no less than 12 areas that can be dealt with, at least partially in the widest sense of the term, as wetlands. But the fact is that waterbirds, as defined by Wetlands International (see Delany & Scott 2006) and are mostly understood by us as well, are actually in the foreground only in three, perhaps four areas (the two coastal wetlands and the Drava River and, conditionally, the intermittent Lake Cerknica). In this context, the Corncrake Crex crex, a grassland bird that in its entire life cycle inhabits much drier habitats than the majority of other representatives of the family Rallidae (SchAffer & Koffijberg 2004), can hardly be considered a waterbird.
The data we have systematically gathered during the past decade at Medvedce reservoir and its vicinity brought us, however, to the point at which we suddenly became aware that we were in possession of yet another wetland of exceptional international and national importance for waterbirds and, on top of it all, of the type that in fact constitutes the highest number of wetlands included in IBAs in Europe — a continental, standing water body (57% of all IBAs defined as wetlands Heath & Evans 2000). Today, a significant part of this type of wetlands consists of fishponds, therefore of that particular type of use that has been carried out in the last few years at the reservoir as well and is, as a matter of fact, responsible for the origin of the water body inside the highwater levee, in the shape as known today. Semi-natural, extensively managed fishponds are characteristic of Central and Eastern Europe (Petkov 2006), including Slovenia, where we do not possess, however, such huge fishfarming complexes as can be found in Croatia, Hungary and Serbia (see LovàSZI 2002, Radovic et al. 2005, Heath & Evans 2000). Nonetheless, the breeding birds of the greatest conservation importance at Medvedce reservoir are similar to those found in the above-mentioned countries. A special mention should be made of the Ferruginous Duck Aythya nyroca, a species of global conservation concern and a characteristic breeding bird of shallow and overgrown standing waters with its largest population in SE Europe. In Slovenia, the Ferruginous Duck has been until recently considered an irregular breeding bird. In the last few years, however, it has turned out that it breeds regularly at Medvedce reservoir and, in 2009, the number of its breeding pairs rose to twelve. The reservoir is currently the extreme NW point of the Ferruginous Duck's more or less continuous breeding range in this part of Europe. Considering the present trend, it can be expected that in a few years its population at the reservoir will reach the criterion for Medvedce becoming a globally important area for this species (20 pairs).
If, on the one hand, we can substantiate the significance of the reservoir for breeding bird with all certainty, it is difficult to do the same for the species that merely migrate over this area, in spite of the excellent quantitative ornithological data presented in this issue of our journal. Here we must underline that according to these data no species occurs here with more than 1% of a biogeographic population, which is one of the criteria for declaring an IBA for non-breeding
species. With daylong counts during the migration period, however, we may succeed in confirming this in the ensuing years for the Lapwing Vanellus vanellus, eventually, the Great Egret Casmerodius albus whose numbers are still increasing. A fairly pertinent and well known fact is that for such small areas, as is Medvedce reservoir with its immediate surroundings, it is difficult to meet — in practice — the above-mentioned criteria that happen to be very high for the majority of species. And what about other species? As an example, let us take the Wood Sandpiper Tringa glareola. The species breeds mostly in Northern Europe and migrates along a wide belt across the entire continent, where its stops mainly at continental wetlands. As it very rarely congregates in large flocks, only one area is known in Europe outside its breeding range, where 1% of its biogeographic population (10,500 individuals) is known to occur (Delany et al. 2009). It is obvious that the conservation concept, which is concentrated on a relatively small number of most important areas, proves a complete failure for this particular species. The recently published research from a small artificial wetland in Austria, aided by individual marking, has shown that the stops by Wood Sandpipers during their spring migration are very short. The number of simultaneously occurring individuals in the area was low, while the turnover was high. A characteristic feature of this species is also its »hopping« migration strategy, when the migrating birds cover, only short distances at a time, with numerous intermediate stops. The message is that for this kind of species the preservation of a thick network of wetlands, small though as they may be, along their migration routes is of utmost importance for their survival (Muraoka et al. 2009). There are certainly more species of this kind, but unfortunately no similar wetlands have been preserved in Central Europe, for many have been destroyed during the past few decades. The same can be said of the wider surroundings of Medvedce reservoir, as well as of Dravsko and Ptujsko poljes. This is yet another reason, therefore, why Medvedce reservoir is of such exceptional significance for this part of the world.
In 2008, BirdLife International proclaimed Medvedce reservoir, under the name of »Crete«, an Important Bird Area (IBA). Together with this, the basis for the proclamation of a special protection area (SPA) was prepared according to the EU Bird Directive (79/409/EGS) and its inclusion into Natura 2000 sites which, however, we are still waiting for. At a Biogeographical Seminar for the Continental Region, held in 2006, it became evident that Medvedce reservoir should also have been proclaimed a potential site of community interest (pSCI) for habitat types (Zagmajster & Skaberne 2006), which are important for birds as well. This, too, has not been implemented to date, even though the establishment of suitable forms of institutional protection is the first indispensable step in the conservation of a particular area. At Medvedce reservoir and its immediate surroundings, increasing threats have been noted in the last few years, both in terms of their extent and intensity. Certain initiatives have also been heard that would, in the event of their implementation, drastically increase the extent of disturbances in the area under consideration. The time to act in favour of a long-term conservation of this unique habitat is now, for tomorrow it could be too late! This thematic number of our journal, which is dedicated in its entirety to Medvedce reservoir, thus has a wider significance. It is also intended for all managers and active users of this area as well as various decision makers — hunters, fishfarmers, councils, national nature conservation services, etc. Without their participation, it will no doubt be lost for good.
Luka Božič
Literatura / References
BirdLife international (2004): Birds in Europe: population estimates, trends and conservation status. — BirdLife Conservation Series No. 12. BirdLife International, Cambridge.
Božič, L. (2003): Mednarodno pomembna obmo~ja za ptice v Sloveniji 2. Predlogi Posebnih zaš~itenih obmo~ij (SPA) v Sloveniji. - Monografija DOPPS št. 2. Društvo za opazovanje in prou~evanje ptic Slovenije DOPPS, Ljubljana.
Delany, S. & Scott, d. (2006): Waterbird population estimates. Fourth Edition. -Wetlands International, Wageningen.
Delany, S., Scott, D., Dodman, T. & Stroud, D. (eds.) (2009): An Atlas of Wader Populations in Africa and Western Eurasia. - Wetlands International, Wageningen.
Heath, M.F. & Evans, M.I. (eds.) (2000): Important Bird Areas in Europe. Priority sites for conservation. — BirdLife Conservation Series No. 8. BirdLife International, Cambridge.
LovâSZI, P. (ed.) (2002): Proposed Special protection areas in Hungary. - MME / BirdLife Hungary.
Muraoka, Y., Schulze, C.H., Pavličev, M. & Wichmann, G. (2009): Spring migration dynamics and sex-specific patterns in stopover strategy in the Wood Sandpiper Tringaglareola. - Journal of Ornithology 150 (2): 313-319.
Petkov, N. (2006): The importance of extensive fishponds for Ferruginous Duck Aythya nyroca conservation. pp. 733-734 In: Boere, G.C., Galbraith, C.A. & Stroud, D.A. (eds.): Waterbirds around the world. - The Stationery Office, Edinburgh.
Polak, S. (ed.) (2000) : Mednarodno pomembna obmo~ja za ptice v Sloveniji. Important Bird Areas (IBA) in Slovenia. - Monografija DOPPS št. 1. Društvo za opazovanje in prou~evanje ptic Slovenije DOPPS, Ljubljana.
Radovic, D., Kralj, J., Tutiš, V., Radovic, J. & Topic, R. (2005): Nacionalna ekološka mreža - važna podru~ja za ptice u Hrvatskoj. - Državni zavod za zaštitu prirode, Zagreb.
SchäFFER, N. & Koffijberg, K. (2004): Crex crex Corncrake. - BWP Update 6 (1/2): 55-76.
ZagmajsTER, M. & Skaberne, B. (2006): Pregled kon~nih odlo~itev Biogeografskega seminarja - Celinska regija, z vklju~enimi NVO stališ~i. - Darova (CZ), 26.-28. 4. 2006.