Avtor/Urednik		Božič, Ivo A
Naslov		Gnezditvena biologija rakarja Acrocephalus arundinaceus na ribnikih v Dragi pri Igu na Ljubljanskem barju (Slovenija)
Prevedeni naslov		Breeding biology of the great reed warbler Acrocephalus arundinaceus at Draga fish-ponds near Ig (Ljubljansko barje, Slovenija)
Tip		članek
Vir		Acrocephalus
Vol. in št.		Letnik 20, št. 97
Leto izdaje		1999
Obseg		str. 177-88
Jezik		slo
Abstrakt		During 1981-1999, the breeding biology of the Great Reed Warbler was monitored at the 16.6 ha large system of discharge fish-ponds at Draga near Ig at Ljubljansko barje. 328 nests were found during the entire period. In the breeding season I visited the fish-ponds 25 times on average per year. The annual breeding success oscillated between 24% and 86%, while in the entire period its average was 56%. The smallest distance between two occupied nests was 3 ni. The majority of the nests were built in common reed Phragmites australis above the water level and only in two cases above solid earth; once it was built in great reedmace Typha sp. and once in rush Juneus sp. The nests were situated SS cm above the water level on average and supported by 5-6 reed stalks. The average depth of the water under the nests was 64 cm. The average height of the nests was 11.8 cm, the average diameter 10.2 cm, and the average depth of the nest cup 7 cm. The first eggs were laid on May 3rd, the majority of them on May 15th. The average size of the 1,027 measured eggs was 22.8 x 16.4 mm, their average weight reaching 2.9 g. Most of the nests contained 5 eggs (2-6), or 4.8 on average. Only about 6% of the Great Reed Warbler pairs built the second nest as well. The number of eggs in the 27 second clutch nests was 2-5, or 3.4 on average. The hatched young weighed about 2.3 g; in three days they doubled this figure and after a week reached the weight of their parents. After 10-12 days they left their nests, even before being able to fly. There were normally 4 or 5 (even 6) young in the nests, exceptionally a single chick (3.9 on average). The successfully fledged nests contained 3.7 chicks, or 2:2 young per all found nests 655 chicks were ringed in their nests. (Abstract truncated at 2000 characters)
Izvleček		V obdobju 1981 - 1999 sem spremljal gnezditveno biologijo rakarja na 16,6 ha velikem sistemu pretočnih ribnikov v Dragi pri Igu na Ljubljanskem barju. V celotnem obdobju sem našel 328 gnezd. V gnezditvenem obdobju sem ribnike obiskal v povprečju 25-krat na leto. Gnezditveni uspeh je nihal med 24% in 86% na leto, v celotnem obdobju pa je bil v povprečju 56%. Najmanjša razdalja med dvema zasedenima gnezdoma je merila 3 m. Večina gnezd je bila zgrajena med stebli navadnega trsta Phragmites australis nad vodo, le v dveh primerih nad trdimi tlemi in po enkrat na rogozu Typha sp. in bičku Juncus sp. V povprečju je bilo gnezdo 55 cm nad vodo in podprto s 5-6 stebli trsta. Povprečna globina vode pod gnezdom je bila 64 cm. Povprečna višina gnezda je merila 11,8 cm, premer 10,2 cm in globina gnezditvenega lončka 7 cm. Prva jajca v gnezdu so bila izležena 3.5., večina pa okrog 15.5. Povprečna velikost 1027 izmerjenih jajc je znašala 22,8 x 16,4 mm, povprečna teža pa 2,9 g. V večini gnezd je bilo 5 jajc (2 - 6), povprečno 4,8. Le okoli 6% parov je zgradilo tudi drugo gnezdo. število jajc v 27 gnezdih drngega legla je bilo 2 - 5, povprečno 3,4. Izvaljeni mladiči so tehtali okrog 2,3 g, v treh dneh so težo podvojili in po dobrem tednu dosegli telesno težo odraslih ptic. Po 10-12 dneh so mladiči še pred letenjem gnezdo zapustili. V gnezdu je bilo običajno 4 ali 5 mladičev, tudi 6, izjemoma en sam mladič (povprečno 3,9). Ob speljavi je bilo v gnezdu v povprečju 3,7 mladiča na uspešno izpeljano gnezdo oziroma 2,2 mladiča na vsa najdena gnezda. Na ribnikih sem v gnezdih obročkal 655 mladičev. število gnezdečih parov rakarja na ribnikih v Dragi od leta 1989 upada (slika 3). Vzroki so predvsem v neprimerni košnji in požiganju trsta, naseljevanju rastlinojedih rib (beli amur Ctenopharyngodon idella), umetno povzročeni prenizki gladini vode v obdobju gnezditve in v prekomernem vznemirjanje rekreativcev.
Deskriptorji		BIRDS ECOSYSTEM POPULATION DYNAMICS BEHAVIOR, ANIMAL NESTING BEHAVIOR EGGS SEASONS