Acoustic properties of humpback whale songs

Abstract

A vertical array of five hydrophones was used to measure the acoustic field in the vertical plane of singing humpback whales. Once a singer was located, two swimmers with snorkel gear were deployed to determine the orientation of the whale and position the boat so that the array could be deployed in front of the whale at a minimum standoff distance of at least 10 m. The spacing of the hydrophones was 7 m with the deepest hydrophone deployed at a depth of 35 m. An eight-channel TASCAM recorder with a bandwidth of 24 kHz was used to record the hydrophone signals. The location (distance and depth) of the singer was determined by computing the time of arrival differences between the hydrophone signals. The maximum source level varied between individual units in a song, with values between 151 and 173 dB re 1 microPa. One of the purposes of this study was to estimate potential sound exposure of nearby conspecifics. The acoustic field determined by considering the relative intensity of higher frequency harmonics in the signals indicated that the sounds are projected in the horizontal direction despite the singer being canted head downward anywhere from about 25 degrees to 90 degrees. High-frequency harmonics extended beyond 24 kHz, suggesting that humpback whales may have an upper frequency limit of hearing as high as 24 kHz.

Source levels of social sounds in migrating humpback whales (Megaptera novaeangliae)

“…This was close to levels estimated by both Winn et al (1971) andFrankel (1994). One of the latest and most comprehensive studies to date used a vertical hydrophone array deployed close to the whale (about 10 m) and therefore should have had minimal errors in TL estimations between the source and the receiver (Au et al, 2006). This study found song unit source levels (broadband, 100 Hz to 15 kHz) to range from 144 to 173 dB re 1 lPa @ 1 m (rms) close to the range of levels found by Levenson (1972).…”

“…This study found song unit source levels (broadband, 100 Hz to 15 kHz) to range from 144 to 173 dB re 1 lPa @ 1 m (rms) close to the range of levels found by Levenson (1972). The Au et al (2006) study also found evidence of intraspecific variation (due to difference in source levels of different units) as well as interspecific variation and therefore reported levels for various different song units within each of the three recorded singers. To date, there is only one published study that reports source levels of social sounds in humpback whales.…”

Using accelerometers to determine the calling behavior of tagged baleen whales

“…Most of these methods are problematic for analyzing baleen whale sound production when conspecifics are present because tagged whale sounds cannot be easily distinguished from those of nearby animals given the typical long-range propagation of low-frequency calls. Another potentially complicating factor is that individuals may vary the source level of generated sounds (Au et al, 2006;Parks et al, 2011), making received level an unreliable indicator of range to the caller. However, recent increases in the sampling capacity of digital recording tags provide new opportunities to assess the calling behavior of individual whales.…”

Humpback whale, <i>Megaptera novaeangliae</i>, song during the breeding season in the Gulf of Tribugá, Colombian Pacific

“…Three distinct themes (Figure 1) were found in each song, and these were composed of 11 units (Figure 2,Table S1 (modeled after the approach of Au et al 2006)). In total, approximately 158.5 minutes of theme 1, 42.5 minutes of theme 2, and 18 minutes of theme 3 were recorded.…”