A population study of Dipper Cinclus cinclus in the Italian Prealps

Fracasso G., Tasinazzo S., Faccin F.

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he Dipper population breeding in a 12.5 km stretch of the River Posina (Vicenza Prealps, northeastern Italy) was studied during 1991-1996 and results were compared with those from other researches throughout Europe. The breeding density (mean = 1.46 ± 0.04 pairs/km) was relatively constant through years, but it was highly variable along the stream. A total of 127 nests were located, most of them (81.1%) built in artificial sites. The median laying date was 9 March for first breeding attempts and 23 April for second ones. Laying dates of first clutches were influenced by pair age and habitat features of the different stream stretches. The overall mean clutch size was 5.11 ± 0.54, comparable with values observed in northern populations of continental Europe. Clutch size did not vary during the season, apart from a sharp decrease in May. Of 54 successful first nestings, 25 (46.3%) were followed by a genuine second brood. The overall percentage of nests producing at least one young was 80.8%, second clutches being more successful than first and replacement ones. Young from clutches laid in different periods showed different recapture rates, nestlings hatched around mid-May showing the highest recapture rate. The annual adult survival rate, estimated from between-year recaptures, was 56.8%. Posina Dippers exhibited a strong territory fidelity both during the breeding season and in the following years.