T. Laskemoen, O. Kleven, F. Fossøy, ja J. T. Lifjeld, ”Intraspecific variation in sperm length in two passerine species, the Bluethroat Luscinia svecica and the Willow Warbler Phylloscopus trochilus”, Ornis Fenn, vsk. 84, nro 3, ss. 131–139, syys 2007.