Wallgren, H. “On the Dependence of Standard Metabolism Upon Enviromental Temperature in the Yellow Bunting (Emberiza Citrinella L.), and the Ortolan Bunting (E. Hortulana L.)”. Ornis Fennica, vol. 29, no. 2, July 1952, pp. 44–48, https://ornisfennica.journal.fi/article/view/132546.