J. Ulfvens, “Population and colony site dynamics in Black-headed Gulls Larus ridibundus breeding on the Finnish west coast”, Ornis Fenn, vol. 70, no. 2, pp. 96–101, Jul. 1993, Accessed: Nov. 25, 2025. [Online]. Available: https://ornisfennica.journal.fi/article/view/133369