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L. Karlsson, S. Ehnbom, and G. Walinder, “A comparison between ringing totals at Falsterbo, SW Sweden, ringing totals at Ottenby, SE Sweden, and point counts from the Swedish Breeding Bird Census during 20 years (1980—1999)”, Ornis Svec, vol. 15, no. 4, pp. 183–205, Oct. 2005.