Song Characteristics of Different Baleen Whales : A New Approach to Sound Analysis. Pranab Kumar Dhar, Jong-Myon Kim

Transcription

1 Song Characteristics of Different Baleen Whales : A New Approach to Sound Analysis Pranab Kumar Dhar, Jong-Myon Kim

2 90 > Abstract This paper presents the characteristics of different baleen whale songs in terms of time domain, frequency domain, and spectrogram representation. The song characteristics for each whale are analyzed with four parameters including peak frequency, frequency range of song, song duration, and pattern of song production. Experimental results for six different baleen whales (humpback, fin, blue, right, minke, and bowhead) indicate that each whale song has unique characteristics that can be quantified. The whale songs used in this study are recorded from different oceans of the world. Humpback whales of Cordell North Canyon produce the highest peak frequency (1348 Hz), whereas blue whales of North Eastern Pacific produce the lowest peak frequency (18 Hz). The humpback whales generate the maximum frequency range of song from 600 Hz to 2800 Hz, whereas fin whales generate the minimum frequency range of song from 10 Hz to 40 Hz. This paper also analyzes the pattern of song production for each whale. Humpback, Minke, and right whales produce similar repeated base unit of song, whereas bowhead, blue, and fin whales produce same repeated base unit of song. These evaluation techniques can provide solutions for characterizing specific features of whale songs. Key words : Whale Song ( ), Whale Song Analysis ( ), Baleen Whales ( ) Over the past decade, there has been an increased effort to understand the characteristics of marine mammals (Green et al., 1994 and Richardson et al., 1995). Many marine mammals rely on sound for communication, navigation, or detection of predators. Whales are one of the marine mammals which use sound to attract mates, repel rivals, communicate within a social group or between groups, navigate, or find food. Different species of baleen whales produce distinct sounds, such as songs, moans, clicks etc. The word song is used to represent the pattern of regular sounds produced by whale. It has a predictable structure with a series of sounds. The whale can sing a song for more than 30 minutes on repeat. The songs, which can last up to 30 minutes, probably communicate species, location, mate status, and readiness to compete with other males for mates. More analysis of the behavior and song is needed before the true function of whale songs is known. Humpback whales are the best known of all the baleen whales for their songs and found in all oceans of the world. These whale sounds were recorded in shallow water, low-latitude, and breeding areas as well as at high latitude feeding areas in deep water. They produce high intensity and low frequency sound (Clapham and Mattila, 1990). Generally, humpback whale can produce sound for long period (Chu,1988).

3 < 91 Right whales have occurred historically in all the world's oceans from temperate to sub polar latitudes. Their vocalizations are categorized into up, down, high and hybrid calls based on the various physical characteristics including pulsiveness of the sounds and frequency modulation characteristics (Clark, 1982). In a study of the northern right whale, Kraus (1991) observed that they have a high rate of vocalizations (average 12 per minute) in active groups in which a female was identified as the centre of activity. Blue whales are found along or offshore of the continental shelf in all oceans of the world. Clark and Fristrup (1997) provided the descriptions and illustrations of blue whales sound from different oceans. Edds (1982) described the sound of the North Atlantic whale based on single recording of seven sounds. Mellinger and Clark (2003) reported that the blue whale sound has infrasonic frequency range, and it occurred in the pattern of sequence variations. They can produce organized sound sequence known as song. Bowhead whales are found in five separate populations in the Arctic Ocean, migrating north and south with the seasonal movement of the edge of the pack ice. Cummings and Holliday (1987) described that these whale sounds have been recorded from Canadian Beaufort Sea. These sounds consist of various lowfrequency (25 to 900 Hz) moans and well defined sound sequences organized into songs ( Hz). Fin whales are distributed worldwide, and they are usually found in higher latitudes in the summer. These whale sounds are relatively simple compared to most other baleen species. The most common fin whale sound is referred to as "20-Hz pulse". This sound is loud and low frequency (15-30 Hz). It has a duration on the order of second (Watkins, 1981). There is variability in the specific acoustic characteristics of pulses (e.g., frequency, duration, and intensity) and in the timing pattern of pulses within a sequence (Patterson and Hamilton, 1964, Edds, 1988). Minke whales are mostly found in north Atlantic, north pacific oceans, and the dwarf subspecies in the Antarctic. Schevill and Watkins (1972) described that the Antarctic minke whale sounds have been recorded in the Ross Sea, and they make low-frequency down swept vocalization. These sounds were described as sweeping from over 100 Hz down to 90 Hz (St. Lawrence Estuary) or 60 Hz (Ross Sea). Prior studies have primarily focused on a single whale in isolation and have analyzed the characteristics for its sound, whereas we study six different types of baleen whale songs in this paper. Our contribution is unique as we do not focus exclusively on a single whale, and we study the characteristics of six different baleen whale songs in terms of time domain, frequency domain, and spectrogram representation. In addition, we identify the different features such as song duration, peak frequency (frequency with peak energy), frequency range of song, and pattern of song production of each whale song. The time domain representation of song represents the base unit of song duration and pattern of song production where we define the smallest unit of song as base unit; the frequency domain representation of song represents the peak frequency and frequency range of song; the spectrogram represents the complex time-frequency representation of song. The rest of this paper is organized as follows. Section II describes analysis parameters of the sampled

4 92 > waveform data of whale songs in term of time domain, frequency domain and spectrogram representation. Section III analyzes the experimental results of six different baleen whale songs. Section IV summarizes and discusses the results of whale songs, and Section V concludes this paper. Time domain, frequency domain, and spectrogram representation of each whale song form the basis of the analysis study. More details for these analysis methods are described below. For time domain analysis, we calculate the number of base unit of song as well as the pattern of song production for each whale song. We also calculate the maximum and minimum amplitude value as well as the duration for each base unit of whale song. A particular song of each whale is represented in a form of frequency spectrum. This analysis employs a fast Fourier transform (FFT) of whale song. We calculate the peak frequency (the frequency with peak energy) as well as the frequency range of song. Each whale song is represented in spectrogram. The spectrogram parameters consist of a discrete Fourier transform (DFT) size of 512 points, a Hanning window, and an overlap size of 50% in which we analyze the energy distribution for each whale song in complex time-frequency domain. This section presents analysis of songs of six different baleen whales: humpback, right, blue, bowhead, fin, and minke.

5 < 93 We study the humpback whale song which was recorded from one of the feeding ground on Cordell Bank Canyon, off the cast of San Francisco, CA. The duration of the selected acoustic file for the humpback whale is 13.4 second, and four base units of humpback whale songs are detected for this duration as shown in Figure 1. We select and analyze the first one for this study. The sampling rate and the number of samples of the acoustic file are 11 khz and , respectively. Experimental results in the time domain representation indicate that the humpback whale produces similar repeated base unit of song and its song duration is nearly 2.75 second. The maximum and minimum normalized amplitude value of the song is and respectively. The results in the frequency domain representation of the selected song indicate that the highest peak frequency is at 1348 Hz. In addition, the song has three sharp peak frequencies: 673 Hz, 2015 Hz, and 2669 Hz. We observe that the frequency components between 600 Hz to 2800 Hz are significant; the other frequency components are not significant. Thus, the frequency range of the selected humpback whale song is from 600 Hz to 2800 Hz approximately. The results in the spectrogram representation indicate that there are four horizontal banding with equally spaced and higher energies are distributed in these bands. Figure 1 shows the time domain, spectrogram, and frequency domain representation of the humpback whale song. We study the right whale song which was recorded at the North Atlantic Ocean. The duration of the selected acoustic file for the right whale is 10.4 second, and two base units of right whale song are detected for this duration as shown in Figure 2. We select and analyze the last one for this study. The sampling rate and the number of samples of the acoustic file are 11 khz and , respectively. Experimental results in the time domain representation indicate that the right whale produces similar repeated base unit of song and its song duration is almost 2.40 second. The maximum and minimum normalized amplitude value of the song is and respectively.

6 94 > The results in the frequency domain representation of the selected song indicate that the highest peak frequency is at 328 Hz. The song has other small peak frequencies: 1 Hz, 657 Hz and 990 Hz. We observe that the frequency components between 0 Hz to 1300 Hz are significant; the other frequency components are not significant. Thus, the frequency range of the selected right whale song is from 0 Hz to 1300 Hz approximately. The results in the spectrogram representation indicate that there are some horizontal bandings and higher energies are distributed in these bands. Figure 2 shows the time domain, spectrogram, and frequency domain representation of the right whale song. We study the blue whale song which was recorded at the North Atlantic Ocean. The duration of the selected acoustic file for the blue whale is 3.10 min, and four base units of blue whale songs are detected for this duration as shown in Figure 3. We select and analyze the first one for this study. The sampling rate and the number of samples of the acoustic file are 1100 Hz and , respectively Experimental results in the time domain representation indicate that the blue whale produces same repeated base unit of song and its song duration is nearly 18 second. The maximum and minimum normalized amplitude value of the song is and , respectively. The results in the frequency domain representation indicate that it has only one peak frequency at 18 Hz. We observe that the frequency components between 0 Hz to 0 Hz are significant; the other frequency components are not significant. Thus, the frequency range of the selected blue whale song is from 0 Hz to 40 Hz approximately. The results in the spectrogram representation indicate that the whale song has one horizontal banding and most of the energies are distributed

7 < 95 within the band. Figure 3 shows the time domain, spectrogram, and frequency domain representation of the blue whale song. We study the bowhead whale song which was recorded at the Arctic Ocean. The duration of the selected acoustic file for the bowhead whale is 16.5 second. We select and analyze the second one for this study. The sampling rate and the number of samples of the acoustic file are 11 KHz and , respectively. Experimental results in the time domain representation indicate that the bowhead whale produces same repeated base unit of song and its song duration is nearly 2.80 second. The maximum and minimum normalized amplitude value of the song is and , respectively. The results in the frequency domain representation indicate that the highest peak frequency is 245 Hz. The whale song has some small peak frequencies: 170 Hz, 345 Hz, 416 Hz, 725 Hz, 761 Hz, 938 Hz, and 1096 Hz. We observe that the frequency components between 100 Hz to 1900 Hz are significant; the other frequency components are not significant. Thus, the frequency range of the selected bowhead whale song is from 100 Hz to 1900 Hz approximately. The results in the spectrogram representation indicate that the bowhead whale song has some curve bandings and higher energies are distributed within these bands. Figure 4 shows the time domain, spectrogram, and frequency domain representation of the bowhead whale song. We study the fin whale song which was recorded from Eastern North Atlantic Ocean. The duration of the selected acoustic file for the fin whale is 83 second, and five base units of fin whale song are detected for this duration as shown in Figure 5. We select and analyze the third one for this study. The sampling rate and the number of samples are 1100 Hz and 91520, respectively. Experimental results in the time domain representation indicate that the fin whale produces same repeated

8 96 > base unit of song and its song duration is nearly 1.20 second. The maximum and minimum normalized amplitude value of the selected song is and , respectively. The results in the frequency domain representation indicate that the highest peak frequency of the song is 22 Hz. We observe that the frequency components between 10 Hz to 40 Hz are significant; the other frequency components are not significant. Thus, the frequency range of the selected fin whale song is from 10 Hz to 40 Hz approximately. The results in the spectrogram representation indicate that most of the energies of the fin whale song are concentrated around the peak frequency (represented as a black spot in spectrogram). Figure 5 shows the time domain, spectrogram, and frequency domain representation of the fin whale song. We study the minke whale song which was collected near Hawaii. The duration of the selected acoustic file for the minke whale is 27.4 second, and four base units of the minke whale song are detected for this duration as shown in Figure 6. We select and analyze the second song for this study. The sampling rate and the number of samples of the sound are 11 KHz and , respectively. Experimental results in the time domain representation indicate that the minke whale produces almost similar repeated base unit of song and its maximum song duration is about 4 second. The maximum and minimum normalized amplitude value of the minke whale song is and , respectively. The results in the frequency domain representation indicate that the highest peak frequency is 33 Hz and the whale song has many peak frequencies: 22 Hz, 50 Hz, 60 Hz, 91 Hz, 121 Hz, 175 Hz, and 234 Hz etc. We observe that the frequency components between 0 Hz

9 < 97 to 1900 Hz are significant; the other frequency components are not significant. Thus, the frequency range of the selected minke whale song is from 0 Hz to 1900 Hz approximately. The results in the spectrogram representation show that the minke whale song has some horizontal bandings and higher energies are distributed in these bands. Figure 6 shows time domain, spectrogram, and frequency domain representation of the minke whale song. We have analyzed the characteristics of different baleen whale songs in term of time domain, frequency domain, and spectrogram representation. Experimental results indicate that different whales produce different songs in both time and frequency domain. We also observe that the sound duration is distinct for each whale song and each whale produces different peak frequency (the frequency with peak energy). The results in the time domain representation indicate that the blue whale produces the maximum duration of base unit of song (18 second), whereas the fin whale produces the minimum duration of base unit of song (1.20 second). We can group the whales in terms of pattern of song production. The fin, blue, and bowhead whales produce same repeated songs, whereas the humpback, minke, and right whales produce almost similar repeated songs. The results in the frequency domain representation indicate that the humpback whale produces the highest peak frequency of 1348 Hz, whereas the blue whale produces the lowest peak frequency of 18 Hz. The humpback whale produces the maximum frequency range of song from 600 to 2800 Hz, whereas the fin whale produces the minimum frequency range from 10 to 40 Hz. Table I summarizes the characteristics of different baleen whale songs.

10 98 > In this paper, we have presented and analyzed the characteristics of different types of baleen whale songs in terms of time domain, frequency domain, and spectrogram representation. We have also identified specific features for each whale such as base unit of song duration, frequency range of song, peak frequency (frequency with peak energy), and pattern of song production. Experimental results indicate that each whale song has unique characteristics. The blue whale produces the longest duration of base unit of song (18 second), whereas the fin whale produces the shortest duration of base unit of song (1.20 second). The humpback whale produces the highest peak frequency (1348 Hz), whereas the blue whale produces the lowest peak frequency (18 Hz). The humpback whale produces the maximum frequency range of song from 600 to 2800 Hz, whereas the fin whale produces the minimum frequency range from 10 to 40 Hz. These evaluation techniques can provide solutions for characterizing the features of whale songs. This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government(mest) (No. R ). [1] K. C. Chu, Dive times and ventilation pattern of singing of humpback whales (Megaptera novaeangliae), Can. J. Zoology, Vol. 66, pp , [2] P. J. Clapham, and D. K. Matilla, Humpback whale songs as indicators of migration routes, Mar. Mamm. Science, Vol. 6, No 2, pp , [3] C. W. Clark, The acoustic repertoire of the Southern right whale, a quantitative analysis, Anim. Behavior, Vol. 30, pp , [4] C. W. Clark and K. M. Fristrup Whales '95: A combined visual and acoustic survey of blue and fin whales off Southern California, Rep. Intl. Whal. Communication, Vol. 47, pp , [5] W. C. Cummings and D. V. Holliday, Sounds and source levels from bowhead whales off Pt. Barrow, Alaska, J. Acoust. Soc. America, Vol. 82, pp , [6] P. L. Edds, Vocalizations of the blue whale, Balaenoptera musculus, in the St. Lawrence River, J. Mammal, Vol. 63, pp , [7] P. L. Edds, Characteristics of finback Balaenoptera physalus, vocalizations in the St. Lawrence River, Bioacoustics, Vol. 1, pp , 1988.

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