Pulliainen, E., Helle, P. and Tunkkari, P. 1981. Adaptive radiation of the digestive system, heart and wings of Turdus pilaris, Bombycilla garrulus, Sturnus vulgaris, Pyrrhula pyrrhula, Pinicola enucleator and Loxia pytyopsittacus. Ornis Fennica. 58, 1 (Mar. 1981), 21–28.