U. Wiktander, I. N. Nilsson, S. G. Nilsson, O. Olsson, B. Pettersson, and A. Stagen, “Occurrence of the Lesser Spotted Woodpecker Dendrocopos minor in relation to area of deciduous forest”, Ornis Fenn, vol. 69, no. 3, pp. 113–118, Sep. 1992.