Populationsutveckling och häckningsframgång för brunand Aythya ferina vid Angarnsjöängen, Uppland, 1995—2005

Abstract

Abundance of wildfowl has been censused annually since 1978 at Angarnsjöängen, a shallow formerly drained eutrophic lake near Stockholm, Sweden. It was extensively restored 1992—1993. Breeding success has been monitored since 1995. Here breeding data on Pochard Aythya ferina, collected 1995—2005, are presented. The population showed large fluctuations between 1978 and 2005 and they were not related to the status of the lake. The population varied between 2 and 14 breeding pairs. In four of the eleven years no broods were observed. It is suggested that the main causes for an absence of reproductive success are water level and/or lack of nesting sites. Mean brood size per successful pair was 5.6 pulli, similar to that in Central Europe. Breeding success (number of broods or pulli per breeding pair) was not related to the number of breeding pairs. Mean brood size was positively correlated with breeding success, but mean brood size was not related to the number of breeding pairs, neither was there a correlation between the total production of pulli and the number of breeding pairs.