(1)
Bensch, S.; Nilsson, L. G. R.; Nothagen, P.; Olsson, P.; Åkesson, M. A Chiffchaff Phylloscopus C. Collybita With Mixed Chiffchaff and Willow Warbler Ph. Trochilus song—genetic Evidence. Ornis Svec 2001, 11, 108-111.