481 



speeds, or analyzed by machine, turn 

 out to be a series of pulses or rapidly 

 sequenced, discrete tones. In such 

 cases, we will call each discrete pulse 

 or tone a "subunit.") A series of units 

 is called a "phrase." An unbroken se- 

 quence of similar phrases is a "theme," 

 and several distinct themes combine to 

 form a "song." Finally, a series of songs 

 within which there is no pause longer 

 than 1 minute is termed a "song ses- 

 sion." Some sessions last for hours. 



In summary: subunit < unit < 

 phrase < theme < song < song ses- 

 sion. A diagram is shown in Fig. 1. 



The shortest complete humpback 

 song we have yet timed lasts 7 minutes, 

 and the longest more than 30 minutes. 

 Since these two songs are quite dif- 

 ferent in form and were recorded in 

 different years, they are probably from 

 different whales. But even the same 

 whale, repeating its own song, will 

 show different cycle lengths during a 

 song session. For example, two succes- 

 sive songs of whale III (Fig. 4) last 

 7 minutes and ll'/z minutes, respec- 

 tively. In spite of such variations in 

 length, we call these vocalizations 

 "songs" because they differ primarily 

 in the number of times the phrases of 

 a given theme are repeated. In our 

 sample, the sequence of themes is in- 

 variable, and no new themes are intro- 

 duced or familiar ones dropped during 

 a song session. Except for the precise 

 configuration of some units and the 

 number of phrases in a theme, there is 

 relatively little variation in successive 

 renditions of any individual hump- 

 back's song. Yet, although we will not 

 deal with it in detail here, we must 

 not overlook this variation, for it is 

 obviously an important feature of the 

 songs. 



Besides the variation among succes- 

 sive songs of one individual, there are 

 often large differences among songs 

 sung by different individuals. This 

 raises the question of whether there is 

 a single, species-specific song pattern, 

 or whether each humpback sings its 

 own pattern. All songs of humpback 

 whales that we have heard consist of 

 the following three main sections: (i) 

 trains of rapidly repeated pulses that 

 often alternate with sustained tones; 

 (ii) many short, high-frequency units, 

 most of which abruptly rise in fre- 

 quency; and (iii) lower, more sustained 

 notes that are monotonously repetitious 

 in rhythm and frequency and contain 

 many units that fall in frequency. We 

 feel that these three sections constitute 



a very general, species-specific song 

 pattern. 



Within this very general framework, 

 the many variations sung by individ- 

 uals seem to sort naturally into several 

 distinct categories or song types, the 

 number of which is still unclear. In 

 all song sessions in our sample, each 



whale adheres to its own song type 

 throughout the session. We consider 

 here two song types (designated as 

 types A and B). As will become clear, 

 these two song types have strong sim- 

 ilarities, even though they depart in 

 form markedly at one point. 

 We include three examples of type 



r^'-n 



"-n 



:zr3 



Whale I 



L^r.-:-. 



Ll^L 



J •-' 



1^ 





Whale E 



Zl. 



Whale in ^=^ 





Fig. 6. Theme 1. In this figure, as in Figs. 7 to 9, the enlarged top view shows diagram- 

 malically a typical example of the phrases of which the theme is composed. Beneath, 

 at reduced scale, are tracings of all phrases in each of two songs of whales I, II, and 

 in. No phrases or other sounds are omitted or changed in order, and no lime is left out. 

 Observe, by referring to the enlarged top view, the slow evolution of this phrase. 

 Note that the short pulse train becomes longer and higher in frequency with each 

 repetition. We have aligned each phrase so that each moment of onset of sound is 

 brought out to the left edge of the column. The sequence of phrases within the theme 

 reads from lop lo bottom. Note that in song 1 of whale III, theme I contains more than 

 twice as many phrases as does theme 1 of song 2 of the same whale. 



