The acoustic calls of blue whales off California are described with visual observations of behavior and with acoustic tracking. Acoustic call data with corresponding position tracks are analyzed for five calling blue whales during one 100-min time period. Three of the five animals produced type A-B calls while two produced another call type which we refer to as type D. One of the animals producing the A-B call type was identified as male. Pauses in call production corresponded to visually observed breathing intervals. There was no apparent coordination between the calling whales. The average call source level was calculated to be 186 dB re: 1 Pa at 1 m over the 10 – 110-Hz band for the type B calls. On two separate days, female blue whales were observed to be silent during respective monitoring periods of 20 min and 1 h.

To understand cetacean ecology and habitat, a new component has been added to the CalCOF1 ecosystein studies that have beer) conducted offshore of southern California over the last half century. In 2004, we initiated visual and acoustic line-transect surveys during)(1 CalCOFI cruises and long-term acoustic monitoring at selected CalCOFI stations. Visual monitoring provides excellent data for highly visible species in calm to moderate weather. The most commonly sighted species oil visual surveys conducted between July 2004 and November 2005 were blue, fill, humpback, and sperm whales, and Pacific white-sided, short-beaked common, and long-beaked common dolphins. Blue, fin, and sperm whales were sighted more frequently in summer to fill months, while northern right whale dolphins and Dall's porpoises were sighted more frequently in winter and spring. Spatial patterns of occurrence are evident for all species within the study area.

We assessed the behavioral context of calls produced by blue whales Balaenoptera musculus off the California coast based on acoustic, behavioral, and dive data obtained through acoustic recording tags, sex determination from tissue sampling, and coordinated visual and acoustic observations. Approximately one-third of 38 monitored blue whales vocalized, with sounds categorized into 3 types: (1) low-frequency pulsed A and tonal B calls, in either rhythmic repetitive song sequences or as intermittent, singular calls; (2) downswept D calls; and (3) highly variable amplitude-or frequency-modulated calls. Clear patterns of behavior, sex, and group size are evident for some call types. Only males were documented producing AB calls, with song produced by lone, traveling blue whales, and singular AB calls were more typically produced by whales in pairs; D calls were heard from both sexes during foraging, commonly from individuals within groups. The sex bias evident in AB callers suggests that these calls probably play a role in reproduction, even though the calls are produced year-round. All calls are produced at shallow depth, and calling whales spend more time at shallow depths than non-calling whales, suggesting that a cost may be incurred during D calling, as less time is spent feeding at deeper depths. This relationship between calling and depth may predict the traveling behavior of singing blue whales, as traveling whales do not typically dive to deep depths and therefore would experience little extra energetic cost related to the production of long repetitive song bouts while moving between foraging areas.