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Dispersal and survival of adult Eurasian Spoonbills in Croatia

The colour-ringing of Eurasian Spoonbill Platalea leucorodia in Croatia started in 2003 and until 2017, 785 birds were ringed. About 700 observations were processed, together with almost 350 observations of birds ringed in other countries, mostly Hungary and Serbia. The migration and stopover sites of juvenile and immature birds have already been studied, while analysis of data for adult birds has not been undertaken yet. Observations of adult birds (fourth year and older) during the breeding period (April July) were analysed. In total, there were 104 observations of 41 individuals. Eight birds (nine recoveries) were reported as breeding, while additional 11 birds (19 recoveries) were observed in the close vicinity of breeding colonies. Although some of these observations might indicate prospecting rather than breeding, they all indicate the dispersal range of Croatian Spoonbills and were analysed together. Spoonbills hatched in Croatia disperse in Croatia, Hungary, Serbia, Czechia and Italy, and were found breeding in these countries, at distances of up to 510 km. At Croatian colonies, Spoonbills hatched in Hungary, Serbia, Italy and France (Camargue) were observed. The survival of Croatian birds was modelled based on live encounters using Cormack-Jolly-Seber (CJS) models in programme MARK. Only birds with at least one recovery were included in the analysis, therefore the survival rate of first-year birds was not calculated. 701 recoveries of 193 individuals were entered in the model. The most parsimonious model had 18 parameters. It showed that survival differed between three age classes and was constant, while observation probabilities were time-dependent. Apparent survival rates calculated on the basis of the most parsimonious model were 0.67 2± 0.33 for immatures and 0.808 ± 0.042 for adults. The oldest bird was in its fifteenth year. Although the amount of records collected during the breeding period is still limited, this analysis gives preliminary data about the dispersal and survival rates of adult Spoonbills from Croatian population

Dispersal ; Survival, CJS Model

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