Author/Editor		Denac, Damijan
Title		Prehranjevalna dinamika in pojav znotrajvrstnega kleptoparazitizma v koloniji navadne čigre Sterna hirundo na Ptujskem jezeru (SV Slovenija)
Translated title		Common tern Sterna hirundo feeding dynamice and intraspecific kleptoparasitism in the colony on Ptuj reservoir (Drava river, NE Slovenia)
Type		članek
Source		Acrocephalus
Vol. and No.		Letnik 25, št. 123
Publication year		2004
Volume		str. 201-5
Language		slo
Abstract		Feeding dynamic, choice of foraging sites and intraspecific kleptoparasitism in the Common Tern Sterna hirundo colony on a concrete power line base on Ptuj reservoir (river Drava, NE SLovenia) were studied on 3 Jul 2004. A group of ornithologists performed a whole day colony observation using prepared protocols. Times, directions of arrival of terns with food and terns' behaviour were registered. On the actual observation day we counted 10 chicks, 15 incubating adults and 11 fledged young in the colony. Breeding density was low, maximum 0.14 nests/m2. The highest frequency of feeding chicks was recorded early in the morning (between 5 and 6 AM). During the day their activity decreased and in the evening (from 18 to 20 PM) their feeding frequency increased again. Terns arrived to the colony mostly from the NW direction (41 %), 32% of them arrived from the SE, and 27% were observed hunting on Ptuj reservoir close to the colony. In 35% of the observations, the terns with food were attacked by conspecific kleptoparasitic terns. Attacks were performed by four terns, attacking alone or in group. Kleptoparasitic terns were either attacking others with food in the air or in the colony when terns attempted to feed their young. Attacking in the air was the mosr frequent tactic (90%). Kleptoparasitic terns were feeding their young with the stolen fish. None of the incubating terns were fed by their partners. This was most probably adaptation to the strong kleptoparasitic pressure. Adult birds tried to avoid attacks by delivering fish very quickly to the chicks. We presume that strong kleptoparasitism was caused by a food shortage. It is possible that kleptoparasitism was only a functional response to the temporary suboptimal hunting conditions as the water was muddy to earlier havy rains.
Summary		Dne 3.7.2004 smo opravili celodnevni popis kolonije navadnih čiger Sterna hirundo na betonskem daljnovodnem podstavku na Ptujskem jezeru. Zanimala nas je časovna prehranjevalna dinamika čiger, ki so hranile mladiče, in morebitno pojavljanje znotrajvrstnega kleptoparazitizma. Čigre so najaktivneje hranile mladiče zgodaj zjutraj (med 5.00 in 6.00 uro), čez dan je aktivnost padla in se vnovič povečala proti večeru (med 18.00 in 20.00 uro), a je dosegla le kako četrtino jutranje frekvence. Večina čiger s plenom (41%) je priletela v kolonijo iz smeri SZ, sledile so čigre iz smeri JV (32%), 27% čiger se je hranilo na Ptujskem jezeru v neposredni bližini kolonije. V koloniji smo opazili izrazit kleptoparazitizem, saj je bil zabeležen kar pri 35% prinosa plena. Na takšen način pridobivanja hrane so se specializirale štiri čigre, ki so z ukradenim plenom potem hranile lastne mladiče. Drugim čigram so kradle ribe posamič ali v skupini, med letom in pri predajanju hrane mladiču. Najpogosteje so kradle plen med letom (90%). Hranjenja odraslih valečih čiger nismo opazovali, kar je najverjetneje prilagoditev na močno znotrajvrstno krajo plena. Mladiči in odrasle ptice so se kraji pri predaji hrane skušali izogniti z bliskovito predajo ribe. Močan kleptoparazitizem je najbrž sprožilo pomanjkanje hrane.
Descriptors		BIRDS FEEDING BEHAVIOR BEHAVIOR, ANIMAL ECOSYSTEM