Avtor/Urednik		Vrezec, Al; Kohek, Ksenja
Naslov		Nekaj gnezditvenih navad kozače Strix uralensis v Sloveniji
Prevedeni naslov		Some breeding habits of the Ural owl Strix uralensis in Slovenia
Tip		članek
Vir		Acrocephalus
Vol. in št.		Letnik 23, št. 115
Leto izdaje		2002
Obseg		str. 1779-83
Jezik		slo
Abstrakt		The Ural Owl Strix urctlensis breeding phenology, use of nest-site types, clutch and brood size are presented for Slovenia. The data from 33 nests were analysed. The most common nest-site types are tree holes, semi-holes, and tree stumps, which are usually 8 m high from the ground mostly on the beech Fagus sylvatica. Only exceptionally, Ural Owls bred on the ground, in a raised hide or in a nest box, which suggests that there are sufficient natural nest-sites sdll available in Slovenian forests. The mean clutch size was 2.4 eggs per nest, which is quite low according to other European data. There are two possible explanations for that: (1) high breeding density, which usually means lower breeding success; and (2) low food availabiliry in the prebreeding period, which decreases the clutch size. Fat Dormouse Glis glis seems to be the Ural Owl's main prey in Slovenia, and it reaches its population maximum as late as in July and August. The brood size (2.0 fledglings per brood) is within the range of other European data, suggesting high survival rate of the young. In Slovenia, the Ural Owl starts to breed very late according to data from other countries in Europe; nests with eggs were found between April 1"` and June 11 `", and the last nonflying fledglings outside their nest in August. One of the explanations for such late breeding of the Ural Owl can be the so-called "waiting strategy hypothesis", according to which the female postpones egg laying in anticipation of better food conditions, in Slovenia until the occurreriče of Fat Dormouse in the summer.
Izvleček		Predstavljena je fenologija gnezdenja, gnezditveni prostori, velikost legla in zaroda kozače Strix uralensis v Sloveniji. Zbrani so bili podatki za 33 gnezd. Najpogostejši tip gnezditvenega prostora so dupla, poldupla in drevesni štrclji, ki so v povprečju 8 m visoko, največkrat na bukvi Fagus sylvatica. Izjemoma so kozače gnezdile na tleh, na lovski opazovalnici ali v gnezdilnici, kar kaže na dovoljšno razpoložljivost naravnih gnezdišč v slovenskih gozdovih. Velikost legla je v povprečju 2,4 jajca na gnezdo, kar je malo v primerjavi z drugimi evropskimi podatki. Za to avtorja navajata dva možna vzroka: (1) velika gnezditvena gostota, ki posledično vpliva na manjši gnezditveni uspeh; in (2) slabe prehranske razmere v predgnezditvenem obdobju, ki znižujejo velikost legla. Polh Glis glis, ki je verjetno glavni plen kozače v Sloveniji v gnezditvenem obdobju, namreč doseže svoj populacijski višek šele v juliju in avgustu. Uelikost zaroda s povprečno 2,0 mladiča na zarod je primerljiva z evropskimi podatki, kar kaže na visoko preživetje mladičev. Glede na Evropo začne kozača v Sloveniji gnezditi razmeroma pozno, saj so bila gnezda z jajci najdena med 1. aprilom in 11. junijem, zadnji neleteči mladiči zunaj gnezda pa šele v avgustu. Razlaga za pozno gnezdenje kozače v Sloveniji je lahko t.i. hipoteza o "čakalni strategiji", ko samica čaka na ugodnejše prehranske razmere v okolju, torej na pojav polha poleti.
Deskriptorji		BIRDS ECOSYSTEM NESTING BEHAVIOR SLOVENIA