Isler, M.L., Isler, P.R., Whitney, B.M., Zimmer, K.J. & Whittaker, A. (2009) Species limits in antbirds (Aves: Passeriformes: Thamnophilidae): an evaluation of Frederickena unduligera (Undulated Antshrike) based on vocalizations. Zootaxa, 2305 (1), 61–68.