Acrocephalus 93 (162/163): 165-169, 2014
nove poti za slovensko obrockanje New paths for Slovenian bird ringing
V	poročilu o obročkovalni dejavnosti (Vrezec et al. 2014) avtorji poleg običajnih podatkov o številu obročkanih ptic in pregleda najdb iz tujine podajajo dve novosti, ki si zaslužita podrobnejšo predstavitev. S pregledom in oceno delujočih obročkovalnih lovišč v Sloveniji so postavili temelje za vzpostavitev mreže lovišč s stalnim naporom (CES — Constant Effort Sites), ki so drugod po Evropi že dalj časa močno orodje za monitoring populacij pogostih vrst. Z objavo najzanimivejših lokalnih najdb, ki so prvič tako podrobno predstavljene v tovrstnem poročilu, pa so napravili korak proti večjemu zanimanju za te podatke, ki dajejo vpogled v ključne elemente življenja ptic.
Zamisel o obročkanju s stalnim naporom je vzniknila v 60. letih 20. stoletja v Veliki Britaniji in na Irskem, kjer so obročkovalci-prostovoljci razmišljali, kako bi s svojimi podatki lahko prispevali k monitoringu populacij pogostih vrst ptic, ki se je tedaj ravno začenjal. Poskusi na lokalni ravni so se množili, podatki združevali, poskusna shema obročkanja s stalnim naporom je bila uvedena leta 1981, od leta 1986 pa je sestavni del obročkovalne dejavnosti na Britanskem otočju (Robinson et al. 2009B). Odtlej se je praksa razširila v več evropskih držav in celo čez Atlantski ocean v Severno Ameriko (DeSante 1995). Ta način obročkanja temelji na strogi standardizaciji: lov poteka na stalnih lokacijah, v predpisanem obdobju s predpisanim številom lovnih dni in z vselej enakim številom mrež (Balmer et al. 2004). Ptic ni dovoljeno privabljati s posnetki oglašanja ali hrano, v bližini lovišča naj se tudi ne bi postavljalo gnezdilnic. Vsi ti ukrepi zagotavljajo primerljivost znotraj istega leta in med leti, kar je ključno za kasnejšo analizo.
Obročkanje s stalnim naporom je usmerjeno predvsem v preučevanje gnezdilk in rabi trem medsebojno povezanim ciljem: monitoringu, raziskovanju in upravljanju. Podatki, pridobljeni z obročkanjem, so dobro dopolnilo drugim popisom, predvsem za ptice trstišč, ki jih je s transektnimi popisi težje zajeti. Korelacija med trendi, ugotovljenimi z obročkanjem, ter trendi drugih popisov ni bila dokazana le na državni (Peach 1998), temveč celo na celinski ravni (Saracco 2008). Podatki, zbrani na CES-loviščih, omogočajo tudi izračun osnovnih demografskih indeksov, ki so temelj za razlago populacijske dinamike.
V	Veliki Britaniji so okrog leta 1990 zabeležili občuten upad populacije severnega kovačka Phylloscopus trochilus, predvsem na jugu države. Gnezditveni uspeh je bil v vsej državi enak dolgoletnemu povprečju, preživetje odraslih osebkov, izračunano iz obročkovalnih podatkov, pa je s 45 upadlo na 24 %, kar je bil najverjetneje tudi neposredni vzrok za upad (Peach et al. 1995). Z letom 1993 se je preživetje odraslih osebkov vrnilo na nekdanjo raven, upad se je ustavil, vzrok za spremembo v preživetju pa je ostal nepojasnjen.
Kljub usmerjenosti v zbiranje podatkov na nacionalni in mednarodni ravni je obročkanje s stalnim naporom lahko učinkovito orodje tudi na lokalni ravni. Analiza podatkov s CES-lovišča, kjer so v nekaj letih odstranili velik del okoliških vrbovih (Salix sp.) sestojev, je pokazala, da je bila velika večina sprememb v številčnosti med leti v skladu s trendi na državni ravni, dve vrsti pa sta bili izjemi (Harrison et al. 2000). Število bičjih trstnic Acrocephalus schoenobaenus
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in srpičnih trstnic A. scirpaceus je upadlo, četudi je bil v celotni državi trend izrazito pozitiven. Kasnejši podrobnejši popisi so pokazali, da število trstnic ni upadlo, temveč so se iz vrbovja, kjer so gnezdile prej, prerazporedile v trstičje. Metoda je dobro sledila lokalnim spremembam, kar je pomembno za lokalne varstvene ukrepe in upravljanje, hkrati pa ta primer opozarja tudi na pomen zadostnega števila lovišč na nacionalni ravni.
Eno prvih lovišč s stalnim naporom za monitoring selivk je bilo odprto leta 1974 v Illmitzu ob Nežiderskem jezeru. Podatki od tod in še z dveh podobnih lovišč v Nemčiji so bili eno prvih opozoril o populacijskem upadu številnih evropskih selivk (Berthold 1986). Podatki o vse manjšem številu vračajočih se bičjih trstnic na britanska gnezdišča pa so pokazali povezavo med vremenskimi razmerami v Sahelu in velikostjo gnezdečih populacij v Evropi (Peach 1991). Tovrstne raziskave so še toliko bolj aktualne v luči podnebnih sprememb, saj je pričakovati, da bo njihov vpliv na selivke še posebno velik (Robinson 2009A).
Domala vsa dela, ki povzemajo in predstavljajo obročkovalno dejavnost, v naslovu nosijo besedi "atlas" in "selitev". Če prvi zaradi obstoja zemljevidov ne moremo oporekati, bi drugi lahko očitali, da, vsaj v ožjem pomenu besede, zanemarja pomemben del premikov ptic. Nekatere varstveno pomembne gozdne vrste vsako leto delajo le kratke premike, ki niso za njihovo ekologijo nič manj pomembni, kot je "prava" selitev za kmečko lastovko Hirundo rustica, vendar ostajajo v na videz manj zanimivi kategoriji "lokalnih najdb". Nenazadnje je tudi najdba bele štorklje Ciconia ciconia, obročkane leta 2002 v Beli krajini, ki v vmesnem času ni bila ujeta zunaj Slovenije, lokalna: v posmeh nekaj deset tisoč preletenim kilometrom. K sreči administrativna kategorija ne more biti ovira za radovednost. Obročkanje v Sloveniji se bliža začetku nove in razburljive poti!
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In the latest bid ringing report (Vrezec et al. 2014), its authors present two novelties — apart from usual data on the numbers of ringed birds and an overview of finds of foreign-ringed birds — that deserve a more detailed presentation. With an overview and assessment of the active ringing sites in Slovenia, they laid the foundation for establishing a CES (Constant Effort Sites) network, which has long been a powerful tool for monitoring common species populations elsewhere in Europe. By publishing the most interesting local finds, presented in this report in such detail for the first time, they made a step towards greater interest in these data, which offer an insight into the key elements of the life of birds.
The idea of constant effort (CE) ringing emerged in the 1960s in Great Britain and Ireland, where volunteer ringers were pondering how to contribute, with their data, to the monitoring of populations of common bird species, which had just been launched there. Attempts at the local level were multiplying, data was compiled and in 1981 a trial CE ringing scheme was was launched. Since 1986 it has been an integral part of bird ringing on the British Isles (Robinson et al. 2009B). Since then, this practice has spread to several European countries and even across the Atlantic to North America (DeSante 1995). This mode of ringing is based on strict standardization: trapping takes place at permanent sites, within a prescribed period of time, with a prescribed number of trapping days and always with the same number of nets (Balmer et al. 2004). Birds
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Acrocephalus 95 (162/163): 165-169, 2014
are not allowed to be attracted with the use of playback or food, and there should be no nest boxes placed in the vicinity of trapping grounds. All these measures enable comparability within the same year and between years, which is of course crucial for eventual analyses.
CE ringing is aimed mainly at studying breeding birds and serves the following three interrelated objectives: monitoring, research and management. The data acquired through ringing complement other surveys, particularly for reed bed species, which may be poorly covered with transect surveys. Correlation between trends, ascertained with ringing, and trends of other surveys has not only been proven at a national level (Peach 1998), but even at continental level (Saracco 2008). The data gathered at CE sites also enable calculation of basic demographic indices, which are crucial for the explanation of the birds' population dynamics. Around 1990, a major decline of the Willow Warbler Phylloscopus trochilus was noted in Great Britain, especially in its southern part. In the entire country, the breeding success equalled the long-term average, while the survival of adult individuals, calculated from ringing data, fell from 45% to 24%, which was most probably the direct cause of their decline (Peach et al. 1995). With the year 1993, the survival of adult individuals returned to the former level; the decline stopped, while the cause of the change in their survival remained unexplained.
Despite focusing on data gathering at the national and international levels, the constant effort ringing can be an effective tool at the local level as well. The analysis of data from a CE site, where most of the surrounding Willow (Salix sp.) stands were removed in a few years, has shown that the great majority of changes in abundance of birds between years were in accordance with trends at the national level, while two species were an exception (Harrison et al. 2000). The number of Sedge Warblers Acrocephalus schoenobaenus and Reed Warblers A. scirpaceus fell, even though the trend was unequivocally positive in the entire country. Eventual detailed surveys showed that the number of these two species was not reduced, but that they moved from willow stands where they had bred earlier to the reed beds. The method detected local changes well, which is significant for local conservation measures and management. At the same time, this example calls our attention to the importance of a sufficient number of trapping grounds at the national level.
One of the first CE sites for the monitoring of migratory birds was opened in 1974 at Illmitz along Neusiedl Lake. The data from here and two similar sites in Germany were one of the first warnings about the population decline of numerous European migratory birds (Berthold 1986). The data on the increasingly low number of returning Sedge Warblers to their British breeding grounds indicated a correlation between weather conditions in the Sahel region and the size of breeding populations in Europe (Peach 1991). This kind of research is even more topical in the light of climate change, for it can be expected that its impact on migratory birds will be particularly significant (Robinson 2009A).
Virtually all works that summarize and present ringing activities carry in their titles the words "Atlas" and "Migration". If the first cannot be disputed due to the presence of maps, the other word could be "reproached" on the grounds that it neglects, in the strict sense of the word at least, a significant part of the birds' movements. Some of the conservationally important forest species make
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only short movements each year which, however, are no less significant for their ecology than the "true" migration for the Barn Swallow Hirundo rustica, but remain in the seemingly less interesting category of "local finds". After all, the recovery of a White Stork Ciconia ciconia, which was ringed in 2002 in Bela krajina, but was not caught outside Slovenia in the meantime, is local: in the derision of the tens of thousands of kilometres covered flying back and forth. Luckily, the administrative category cannot be an obstacle to curiosity. Ringing in Slovenia is nearing the beginning of a new and exciting path!
Jurij Hanzel
Literatura / References
Balmer D., Wernham C., Robinson R. (2004): Guidelines for constant effort ringing in Europe. — [http://www.euring.org/research/ces_in_europe/euro_ces_ guidelines210904.pdf], 25/11/2014. Berthold P., Fliege G., Querner U., Winkler H. (1986): Die Bestandsentwicklung von Kleinvogeln in Mitteleuropa: Analyse von Fangzahlen. — Journal of Ornithology 127 (4): 397-437.
DeSante D. F., Burton K. M., Saracco J. F., Walker B. L. (1995): Productivity indices and survival rates estimates from MAPS, a continent-wide program of constant-effort mist-netting in North America. - Journal of Applied Statistics 22: 935-947.
Harrison N. M., Whitehouse M. J., Prince P. A., Huin N. (2000): What problems do local habitat change represent for the Constant Effort Site ringing scheme? — Ringing & Migration 20: 1—8. Peach W., Baillie S., Underhill L. (1991): Survival of British Sedge Warblers Acrocephalus schoenobaenus in relation to West African rainfall. — Ibis 133 (3): 300— 305.
Peach W. J., Crick H. Q. P., Marchant J. H. (1995): The demography of the decline in the British willow warbler population. — Journal of Applied Statistics 22 (5/6): 905—922.
Peach W. J., Baillie S. R., Balmer D. E. (1998): Long-term changes in the abundance of passerines in Britain and Ireland as measured by constant effort mist-netting. —
Bird Study 45: 257—275. Robinson R. A., Crick H. Q. P., Learmonth J. A., Maclean I. M. D., Thomas C. D., Bairlein F., Forchhammer M. C., Francis C. M., Gill J. A., Godley B. J., Harwood J., Hays G. C., Huntley B., Hutson A. M., Pierce G. J., Rehfisch M. M., Sims D. W., Begona Santos M., Sparks T. H., Stroud D. A., Visser M. E. (2009A): Travelling through a warming world: climate change and migratory species. — Endangered Species Research 7: 87—99. Robinson R. A., Julliard R., Saracco J. F. (2009B): Constant effort: studying avian population processes using standardised ringing. — Ringing & Migration 24: 199— 204.
Saracco J. F., DeSante D. F., Kaschube D. R. (2008): Assessing landbird monitoring programs and demographic causes of population change. — Journal of Wildlife
Management 72: 1665—1673. Vrezec A., Fekonja D., Sere D. (2014): Obrockovalna dejavnost in pregled najdb obrockanih ptic v Sloveniji v letu 2013. — Acrocephalus 35 (160/161): 25—58.
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