Common tern Sterna hirundo breeding population

• Main Author: Denac, Damijan
• Format: Other/Unknown Material
• Language: English
• Published: Društvo za opazovanje in proučevanje ptic Slovenije 2015
• Subjects: Lurus Ridibundus; Sterna Hirudo; info:eu-repo/classification/udc/57; Common tern; Sterna hirundo; Black-headed Gull; Larus ridibundus
• Online Access: https://repozitorij.uni-lj.si/IzpisGradiva.php?id=63092; https://repozitorij.uni-lj.si/Dokument.php?id=63103&dn=; http://www.cobiss.si/scripts/cobiss?command=DISPLAY&base=cobib&rid=18726361&fmt=11

A colony of Common Terns Sterna hirundo and Black-headed Gulls Larus ridibundus formed in 1981 in the wastewater basins of the sugar factory in Ormož. From than on, the colony has been monitored regularly by direct counting. The site was flooded in 1994 and, in 1995 and 1996, Common Terns andBlack-headed Gulls did not breed. In 1997> the first artificial breeding raft (surface area 12.5 m2) was placed, followed in 1998 and 2001 by additional rafts (14 m2 and 96 m2, respectively). All rafts were placed with the intention of preserving the Common Tern, since this species is highly endangded in Slovenia. As a result, the biggest mixed Common Tern and Black-headed Gull colony in Slovenia has been established on the artificial brecding rafts. In 2002, 64 pairs of Common Tern and 113 pairs of Blackheaded Gull bred on rafts, amounting to 45% and 50% respectively of the Slovene breeding population. Black-headed Gulls started to breed in higher numbers on the largest rafts, placed in 2001, and, for that reason, the percentage of Terns breeding on the rafts decreased. In 2000 all the Terns, but in 2001 only80% of those in the basins were breeding on rafts. It is most probable that the bigger rafts, with special breeding structures for Common Terns, weremore attractive for Black-headed Gulls. Obviously they liked thc heterogeneous raft surface, because they built their nests on the breeding structures planned to increase the breeding success of Common Terns. Leta 1981 so navadne čigre Sterna hirundo in rečni galebi Larus ridibundus oblikovali novo kolonijo v bazenih za odpadne vode Tovarne sladkorja v Ormožu.Število gnezdečih rečnih galebov in navadnih čiger redno spremljamo z metodo večkratnega štetja s teleskopom. Leta 1994 je zaradi dviga vodne gladine v bazenih kolonijo preplavilo. V letih 1995 in 1996 navadne čigre in rečni galebi v bazenih niso gnezdili. Leta 1997 je bil v bazenih postavljen prvi gnezditveni splav površine 12,5 m-', leta 1998 drugi s površino 14 m` in leta 2001 trije med seboj povezani enaki splavi s skupno površino 96 mz. Postavili smo j ih z namenom, da bi se oblikovala nova kolonija navadne čigre in da bi se ta ptica ohranila kot gnezdilka na tem območj u. Na gnezditvenih splavih je tako nastala največja mešana kolonija navadnih čiger in rečnih galebov v Sloveniji. Leta 2002 je na splavih gnezdilo 64 parov navadnih čiger in 113 parov rečnih galebov. To je 45% slovenske populacije navadnih čiger in 50% rečnih galebov. Rečni galebi so začeli množično gnezditi na splavih šele leta 2001, ko smo namestili tri največje splave. Odstotek gnezdečih čiger na splavih se je zmanjšal: leta 2002 jih je 20% gnezdilo na naplavinah in blatnihpolojih, leta 2000 pa so vse gnezdile na splavih. Menim, da so rečni galebi množično zasedli nove splave zaradi njihove velikosti in heterogene površine. Na splave smo namestili večje število gnezditvenih struktur (strešnike, veje, štore - za kritje mladičem pred dežjem, vročino in plenilci)za navadno čigro. Na teh strukturah so gnezdili rečni galebi.