The myrtle and Audubon’s warblers are genetically and morphologically distinct subspecies of the yellow-rumped warbler (Setophaga coronata) that share a geographical hybrid zone. Although bird watchers know that these taxa are separable by ear based on “chip” call, there has been no systematic examination of the nature of this call variation. We screened 203 recordings of myrtle and 134 recordings of Audubon’s warblers obtained from Xeno-Canto, and selected 10 high-quality recordings from each subspecies for analysis. We then performed waveform and spectrogram analyses to identify quantitative features of selected exemplar calls using Raven Lite. “Chip” calls of the two subspecies were distinct in starting frequency, frequency range, duration, and shape. Specifically, Audubon’s calls began at an average frequency of 3565 Hz, higher than the myrtle call at 3313 Hz. The total duration was longer for Audubon’s calls (0.0272 seconds) than for myrtle (0.0180 seconds). At 0.0091 seconds into the call, myrtle warblers attained an average peak frequency of 6278 Hz and then abruptly dropped in pitch, while Audubon’s frequency increased throughout the call to a peak of 5870 Hz at the end. The frequency range was thus greater for myrtle (3313-6278 Hz) than for Audubon’s warblers (3565-5870 Hz), and myrtle calls rose and then fell in pitch, whereas Audubon’s calls only rose. This study provides a basis for examination of geographic vocal variation across the range of each taxon, and our approach should be considered when looking for hybrid individuals, which may produce intergrade calls. Similar analyses of simple, innate calls of other species with multiple subspecies may prove fruitful.