Eriksson, K. (1969) “On the occurrence of the Grasshopper Warbler (Locustella naevia) and River Warbler (L. fluviatilis) in Finland related to the bird watching activity”, Ornis Fennica, 46(3), pp. 113–125. Available at: https://ornisfennica.journal.fi/article/view/132768 (Accessed: 20April2025).