We analyzed 175 calls of 91 individual Winter (Troglodytes hiemalis) and Pacific (Troglodytes pacificus) wrens by measuring characteristics such as peak frequency, frequency range, and complexity. We found considerable overlap in most measurements, but metrics such as peak frequency and trace shape are useful for distinguishing the two species. With these results, we recommend a standard for acceptance of extralimital Winter and Pacific wrens through evaluation of spectrograms quantifying the call’s peak frequency (higher in the Pacific, lower in the Winter), the shape and symmetry of the trace at the lowest frequency (more symmetrical in the Winter), and whether the lowest-frequency trace is tightly coupled with a second trace (favoring the Pacific).