Siivonen L. Does the Willow Warbler, Phylloscopus trochilus (L.), belong to those species of birds fluctuating greatly in number. Ornis Fenn [Internet]. 31 december 1949 [citerad 18 maj 2024];26(4):89–97. Tillgänglig vid: https://ornisfennica.journal.fi/article/view/132521