Acoustic recordings from Palmyra Atoll, northern Line Islands, central Pacific, showed upsweep frequency modulated pulses reminiscent of those produced by beaked whales. These signals had higher frequencies, broader bandwidths, longer pulse durations and shorter inter-pulse intervals than previously described pulses of Blainville’s, Cuvier’s and Gervais’ beaked whales [
Zimmer et al. (2005). J. Acoust. Soc. Am. 117, 3919–3927
Johnson et al. (2006). J. Exp. Biol. 209, 5038–5050
Gillespie et al. (2009). J. Acoust. Soc. Am. 125, 3428–3433
]. They were distinctly different temporally and spectrally from the unknown beaked whale at Cross Seamount, HI [
McDonald et al. (2009). J. Acoust. Soc. Am. 125, 624–627
]. Genetics on beaked whale specimens found at Palmyra Atoll suggest the presence of a poorly known beaked whale species. Mesoplodon sp. might be the source of the FM pulses described in this paper. The Palmyra Atoll FM pulse peak frequency was at 44 kHz with a −10 dB bandwidth of 26 kHz. Mean pulse duration was 355 μs and inter-pulse interval was 225 ms, with a bimodal distribution. Buzz sequences were detected with inter-pulse intervals below 20 ms and unmodulated spectra, with about 20 dB lower amplitude than prior FM pulses. These clicks had a 39 kHz bandwidth (−10 dB), peak frequency at 37 kHz, click duration 155 μs, and inter-click interval between 4 and 10 ms.