Avtor/Urednik		Ciglič, Henrik; Geister, Iztok
Naslov		Spolna sestava in gnezditvena uspešnost velikega žagarja Mergus merganser na Trbojskem jezeru
Prevedeni naslov		Sex structure and breeding success of the goosander Mergus merganser at Trbojsko jezero
Tip		članek
Vir		Acrocephalus
Vol. in št.		Letnik 16, št. 73
Leto izdaje		1995
Obseg		str. 181-6
Jezik		slo
Abstrakt		From 1993 to 1995, a small population of the Goosader Mergus merganser was monitored during 116 observation days at Trbojsko jezero (Mavčiče Reservoir) on the Sava river, the only known breeding habitat of this bird in Slovenia. In late autumn the bird's wintering community settles at Trbojsko jezero and by the end of February leaves their wintering quarters with already formed pairs. Roughly at the same time (end of February, early March), a breeding community settles there (where new pairs are formed), which is in spring (April) joined by sexually immature individuals. The number of sexually immature males decreases from March onwards, the last one disappearing in mid-May. This is due to moulting, which in sexually mature males takes place, as well known, outside their breeding habitat. Sexually immature individuals of both sexes, however, evidently stay with females. Sex structure of the bird's population and its breeding success were established. In the last two years there were about twice as many females (including sexually immature individuals) as males: 5:4 (1993), 10:4 (1994) and 13:6 (1995), the surplus representing sexually immature individuals of both sexes: 1 (1993), 3 (1994) and 8 (1995). The greatest number of chicks was recorded in 1994: 47 (compared with 25 in 1993, and 26 in 1995), when the breeding success reached its peak (6.7 young per tending female); the breeding was last successful in 1995 (5.5 young per tending female). Considering that in 1994 the number of sexually immature individuals in increased in commparison with the previous year, a greater number of females with the young can be expected in 1996. The males perhaps behaved polygamously in 1994, when the young were led by 7 females in company of males.
Deskriptorji		BIRDS ECOSYSTEM POPULATION DENSITY SEX FACTORS