Schaub, M., M. Müller & G. Pasinelli
(* = Kurzbeitrag)
Demografie einer Population des Neuntöters Lanius collurio bei Ramosch.
(von 1994 bis 2006 vergeben)
Bestandsentwicklung, Bruterfolg, Beringung, Fekundität, Überlebensrate, Emigration, Immigrationsrate, integriertes Populationsmodell
Unterengadin, Graubünden, Schweiz
Demography of a population of the Red-backed Shrike Lanius collurio at Ramosch. Changes in population size of a species are determined by the four key demographic rates fecundity («breeding success»), survival, emigration and immigration. Despite their importance in ecology and conservation biology, and with the exception of fecundity, these key vital rates are hardly known for most species. For a population of the Red-backed Shrike Lanius collurio studied intensively from 1988 to 1992 in eastern Switzerland, we estimated survival rate, breeding success, immigration rate and the composition in terms of age classes and sex with an integrated population model. Number of breeding pairs varied from 58 to 99. Local survival rate showed little temporal variation and was on average for first-year males 0.15 (95 % confidence interval: 0.08–0.31), for first-year females 0.09 (0.06–0.12), for adult males 0.50 (0.42–0.59) and for adult females 0.43 (0.32–0.54). 38 % of all breeding pairs failed to produce fledglings (ntotal = 348), and the mean number of fledglings per breeding pair ranged from 2.48 (2.14–2.83) in 1990 to 3.54 (3.08–4.03) in 1988. Mean immigration rate was 0.36 (0.09–0.66) in females and 0.23 (0.01–0.49) in males. In females, the relative shares of immigrants (42 %) and of surviving adults (46 %), respectively, was similar, while the share of local recruits was considerably lower (12 %). In males, surviving adults made up the largest relative share of the population (56 %), followed by immigrants (25 %) and local recruits (19 %). This population of Red-backed Shrikes was thus demographically open and received individuals from other populations, to which it likely also contributed emigrants. In the discussion, we also compare our findings with a study conducted in southern Germany that had used similar field and analytical methods.
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