1. Overview
29
4. Changes in songs are not due to forgetting during the summer months,
which are nonsinging months, since songs recorded early in the winter
breeding season are nearly the same as songs recorded late in the previous breeding season.
5. Songs from consecutive years are very similar but songs across nonconsecutive years will have fewer similarities.
6. Singers are most probably only males, since no females have been
observed singing.
7. Some singing also occurs during the summer and fall.
8. Singing whales are often alone, although they have been occasionally
observed singing in the presence of other humpback whales.
9. Singers tend to remain stationary, however, they have also been observed
singing while swimming.
An example of a humpback whale song is given by Tyack and Clark
(Chapter 4). They also discuss hypotheses on why humpback whales sing.
One of the interesting findings of the study by Mercado (1995) is the fact
that several sounds that seemed perceptually continuous to human listeners were found to be pulsed when their waveforms were examined more
closely. The pulse repetition rate of ratchet sounds typically increased as the
ratchet theme progressed, causing the spectrogram to look increasingly like
a continuous wave signal with harmonics. Examples of two ratchet sounds
are shown in Figure 1.12, with a portion of the waveform in the top panel
and the corresponding spectrogram in the middle and bottom panels.
Examples of other sound types with a portion of the waveforms above the
spectrograms are shown in Figure 1.12. From the figure, it seems as if there
is a graded structure in the waveform. At a slow repetition rate, the pulsed
nature of the waveform is obvious. The repetition rate can increase to the
point where the signal converges into a more sinusoidal form. Mercado
(1995) stated that all the signals he analyzed had a pulse structure and suggested that humpback whale songs may be more pulselike than previously
believed.
5.1.2 Other Mysticetes
Bowhead whales, B. mysticetus, emit a variety of different types of simple
and complex sounds that sound like moans to the human ear. They also
emit sequential sounds that contain repeatable phrases that can be classified as songs during their spring migration (Ljungblad et aI., Moore 1982)
but not during summer or autumn (Wursig and Clark 1993). The bowhead
song had just one theme with basically only two sounds repeated over and
over. Ljungblad et al. (1982) reported that songs were very tonal with
clear pitch even though they were produced by pulsive moans, whereas
Cummings and Holliday (1987) described songs as sounding like raucous
elephant roars and trumpeting in discrete repetitions or phrases that were
put together to form longer sequences. Differences in the songs recorded
29
4. Changes in songs are not due to forgetting during the summer months,
which are nonsinging months, since songs recorded early in the winter
breeding season are nearly the same as songs recorded late in the previous breeding season.
5. Songs from consecutive years are very similar but songs across nonconsecutive years will have fewer similarities.
6. Singers are most probably only males, since no females have been
observed singing.
7. Some singing also occurs during the summer and fall.
8. Singing whales are often alone, although they have been occasionally
observed singing in the presence of other humpback whales.
9. Singers tend to remain stationary, however, they have also been observed
singing while swimming.
An example of a humpback whale song is given by Tyack and Clark
(Chapter 4). They also discuss hypotheses on why humpback whales sing.
One of the interesting findings of the study by Mercado (1995) is the fact
that several sounds that seemed perceptually continuous to human listeners were found to be pulsed when their waveforms were examined more
closely. The pulse repetition rate of ratchet sounds typically increased as the
ratchet theme progressed, causing the spectrogram to look increasingly like
a continuous wave signal with harmonics. Examples of two ratchet sounds
are shown in Figure 1.12, with a portion of the waveform in the top panel
and the corresponding spectrogram in the middle and bottom panels.
Examples of other sound types with a portion of the waveforms above the
spectrograms are shown in Figure 1.12. From the figure, it seems as if there
is a graded structure in the waveform. At a slow repetition rate, the pulsed
nature of the waveform is obvious. The repetition rate can increase to the
point where the signal converges into a more sinusoidal form. Mercado
(1995) stated that all the signals he analyzed had a pulse structure and suggested that humpback whale songs may be more pulselike than previously
believed.
5.1.2 Other Mysticetes
Bowhead whales, B. mysticetus, emit a variety of different types of simple
and complex sounds that sound like moans to the human ear. They also
emit sequential sounds that contain repeatable phrases that can be classified as songs during their spring migration (Ljungblad et aI., Moore 1982)
but not during summer or autumn (Wursig and Clark 1993). The bowhead
song had just one theme with basically only two sounds repeated over and
over. Ljungblad et al. (1982) reported that songs were very tonal with
clear pitch even though they were produced by pulsive moans, whereas
Cummings and Holliday (1987) described songs as sounding like raucous
elephant roars and trumpeting in discrete repetitions or phrases that were
put together to form longer sequences. Differences in the songs recorded