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The vocal behavior of ziphiid whales is very poorly known. Free-swimming northern bottlenose whales, Hyperoodon ampullatus, have been recorded producing 3-16 kHz whistles and chirps (Winn et al. 1970; linear equipment frequency response 500 Hz-14 kHz) and 20-30 kHz ultrasonic clicks (Fauchner and Whitehead, unpublished data; equipment response to 35 kHz). A free-swimming mesoplodont beaked whale (probably Mesoplodon hertori) produced ultrasonic clicks (Ljungblad, unpublished data; equipment frequency response to 32 kHz). Sounds have been recorded from a stranded Blainville's beaked whale, Mesoplodon densirostris (Caldwell and Caldwell 1971; equipment frequency response 40 Hz-20 kHz) and a post-stranding, captive Hubb's beaked whale, Mesoplodon carlhubbsi (Lynn and Reiss 1992; equipment frequency response 70 Hz-40 kHz). The latter two species produced low-frequency pulses (mostly < 2 kHz). The Hubb's beaked whale also produced broadband clicks extending beyond the limit of the recording gear (> 40 kHz) and a few weak whistles (< 10.7 kHz). During cetacean survey cruises conducted by the National Marine Fisheries Service off the coasts of Oregon, U.S.A., and Baja California, Mexico, we recently made what we believe to be the first recordings of Baird's beaked whales (Berardius bairdii).
On 27 July 1994 the NOAA Ship Snrveyor encountered a group of 30-35 Baird's beaked whales about 225 nmi west of Hecata Head, Oregon (at 44°10'N, 129°10'W). Two sonobuoys (ex U.S. Navy, type 57B) were deployed. The first was deployed 1.6 nmi away from the animals, before a rigid-hulled inflatable boat (RHIB) was launched. The second was deployed 55 min later from the RHIB, within tens of meters from the animals. To relocate the animals after each dive, a continuous search was maintained by two observers searching the forward quadrants with 25X binoculars and two or more additional observers searching all quadrants with 7X binoculars and unaided eyes. The only other cetacean seen during this time was one large sperm whale 6-10 nmi away. Sounds were recorded using a Nagra IV-SJ analog tape recorder, for a total system response from 20 Hz to 20 kHz. We filtered these recordings at 20 kHz (low pass) and digitized them at 44.1 kHz (16 bit). Spectrograms (4096 pt FFT, 1024 pt frame length, 87.5% overlap, 174.85 Hz analyzing filter bandwidth) were generated using Canary™ signal processing software (v. 1.2.1; Cornell University), running on a Power Macintosh™ 760011 20.