Hromada, M., L. Kuczynski, A. Krištín, och P. Tryjanowski. ”Animals of Different Phenotype Differentially Utilise Dietary Niche- the Case of the Great Grey Shrike Lanius Excubitor”. Ornis Fennica, vol. 80, nr 2, juli 2003, s. 71–78, https://ornisfennica.journal.fi/article/view/133594.