Martinez, N. & S. Zingg
(* = Kurzbeitrag)
Zweitbruten beim Gartenrotschwanz Phoenicurus phoenicurus in der Schweiz.
(von 1994 bis 2006 vergeben)
Brutbiologie, Zweitbrut, Brutperiode, Bruterfolg, Nestkarten
Schweiz, Bern, Basel-Stadt, Basel-Landschaft, Solothurn
Second broods in the Common Redstart Phoenicurus phoenicurus in Switzerland. The Common Redstart is generally considered as being a single-brooded species in Switzerland although detailed data are lacking. However, several records of two broods per season from other Central European countries do exist. A few studies conducted in Central Europe have even demonstrated that Common Redstarts frequently have two broods per season, contrarily to birds from Fennoscandia who strictly breed once per year. If these findings represent constant differences between single-brooded populations in the north and partly double-brooded populations in the south, second broods would be expected to be more frequent in Switzerland, too. We evaluated the percentage of second broods in two geographically separated Common Redstart populations in Berne and North-western Switzerland using two different methods. In a first step we estimated the proportion of second broods using egg-laying data and assuming early clutches to be first broods and late clutches to be second broods. For 10 out of 50 clutches from North-western Switzerland egg-laying started after 25 May, the date we used for the differentiation between first and second broods. The proportion of second broods would thus be 20 %. Considering that this approach could be falsified, partly due to an unknown proportion of replacement clutches, we searched for true second broods in territories where young of a first brood had successfully been raised in North-western Switzerland as well as in Berne. Here, from a total of 34 pairs with a successful first brood, 12 pairs started a second brood, meaning that 35 % of the pairs finally bred twice. Differences between regions and years were considerable with an observed range of 25 to 57 % of pairs. Still, our results show that a significant proportion of Common Redstarts in Switzerland readily start with a second brood after the first brood has been raised successfully.
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