Pakkala, T., J. Tiainen, M. Piha, and J. Kouki. “Nest Tree Characteristics of the Old-Growth Specialist Three-Toed Woodpecker Picoides Tridactylus”. Ornis Fennica, vol. 95, no. 3, Sept. 2018, pp. 89–102, doi:10.51812/of.133933.