Comment and update to Frontiers in Zoology 2006, 3: Matina Kalcounis-Rueppell, University of North Carolina at Greensboro 13 January 2014 In Kalcounis-Rueppell et al 2006 (Frontiers in Zoology) we placed ultrasound-recording devices in the field in the presence of resident Peromyscus mice for several weeks during December 2004 and January 2005. In Kalcounis-Rueppell et al 2006, we attributed 7 sound types (or motifs) to Peromyscus mice. Since that publication, we have conducted long-term and intensive field studies at the same field site. In these studies, we have examined the behavioral context of ultrasound production from individual Peromyscus mice from two different species [Peromyscus boylii: Petric and Kalcounis-Rueppell 2013 (Behaviour 150: 1747-1766) and P. californicus: Briggs and Kalcounis-Rueppell 2011 (Animal Behaviour 82:1263-1273)]. We have also compared the ultrasound produced by P. californicus in the field to ultrasound produced by the same species in the laboratory (Kalcounis-Rueppell et al 2010). Overall, our subsequent studies have validated the work in Kalcounis-Rueppell et al 2006. Of the 7 motif types described in Kalcounis-Rueppell et al 2006, 5 are regularly attributed to individual Peromyscus mice in both the field and the lab (motifs a, b, c, f, g in Figure 1 of Kalcounis-Rueppell et al 2006). However, in our subsequent work we have never had individual Peromyscus vocalizations attributed to motifs d and e, and the evidence therefore indicates that mice may not produce these motifs. Rather, we have recorded bat vocalizations that clearly resemble motifs d and e. Thus, although motifs a, b, c, f, g in Figure 1 of Kalcounis-Rueppell et al 2006 are produced by Peromyscus, motifs d and e may be produced by bats. In addition, we have two more updates to Figure 1 in Kalcounis-Rueppell et al 2006 as they relate to motifs a, b, c, and g. Reflecting the fact that none of these motifs are true whistles, we renamed these general forms of motifs as single- or multi- syllable vocalizations (SV). This renaming is described in Kalcounis-Rueppell et al 2010. Accordingly, in Figure 1 of Kalcounis-Rueppell et al 2006, motif a is a 1 syllable vocalization (1SV), motif b is a two syllable vocalization (2SV) and motifs c and g are both 3 syllable vocalizations (3SV). We also recognize motif g as a less modulated version of motif c. For updated, species-specific panels of common USVs produced by wild Peromyscus, we direct the reader to Figure 1 of Petric and Kalcounis-Rueppell (2013) for Peromyscus boylii and Figure 1 of Briggs and Kalcounis-Rueppell (2011) for Peromyscus californicus. Competing interests No competing interests.