556 SCHEVILL, BACKUS, AND HERSEY [CHAP. 14 



(Everest, Young and Johnson, 1948). The "rasping" sound of the langouste, 

 Panulirus argus, has components from 40 c/s to 9000 c/s, with most energy at 

 800 c/s and in the band from 2500 to 7700 c/s. The "slow rattle" covers fre- 

 quencies between 500 c/s and 3300 c/s, with most energy at 600 c/s (Moulton, 

 1957). 



The spectrum of cetacean sounds is in general very broad, reaching right 

 across the scale of such measuring instruments as we have used, say, from less 

 than 30 to about 200,000 cycles per second. This highest figure (Schevill and 

 Lawrence, 1953, p. 163) is probably not biologically significant, being very 

 likely ultrasonic even to the porpoises which produced it, but it is cited to 

 remind us that there may be acoustic energy beyond the reach of our ordinary 

 instruments. Many of these do not reach above 20 kc/s, and so hear at least as 

 well as humans ; at Woods Hole we have sometimes employed systems that 

 were useful to 30 kc/s. Most of the energy of cetacean sounds is within this 

 band ; it is not known how high these animals hear. One experiment (Schevill 

 and Lawrence, 1953) indicates that Tursiops, at least, responds readily to 

 frequencies as high as 120 kc/s. 



We have, unfortunately, no good figures for the intensity of cetacean sounds. 



There are probably of the order of a hundred species, or kinds, of cetaceans. 

 Of these only about a dozen have so far been firmly demonstrated to be soni- 

 ferous, although a good many more figure in unscientific accounts most of 

 which appear to allude to respiratory noises heard at the surface through the 

 air. (These adventitious sounds are only rarely heard under water even by 

 sensitive equipment.) Tomilin (1955), it is true, reports hearing the underwater 

 sounds of many more species than we have, but gives no particulars either of 

 the sounds or of the means by which he heard them. Accordingly, we confine 

 ourselves to the species of which we have particulars, and await further details 

 from him. 



The sounds of the mysticetes (baleen whales) are very poorly known, only 

 Euhalaena and Megaptera having been reliably recorded. The rather sonorous 

 "moans" and strident screeches of Euhalaena (right whale, Nordcaper) have 

 been repeatedly recorded in Cape Cod waters ; Fig. 9 is a spectrogram of one of 

 these calls, showing that the fundamental is below 200 c/s. Megaptera (hump- 

 back whale) also concentrates on low frequencies, albeit a little higher, 300 to 

 400 c/s. We know of no other instrumental data, although older authors (e.g. 

 Aldrich, 1889, pp. 32-35, including "Kelley's Band") have given vivid subjective 

 accounts. 



The sounds of the odontocetes (toothed whales) are better known. In general 

 they appear to consist of whistle-like squeals and impulsive clicks. The clicks 

 may be made singly or in bursts at a repetition rate as high as 400 per second 

 (Schevill and Lawrence, 1956); at these various rates sounds of different 

 characteristics are produced, which have been described as "creaks", "barks", 

 "snores", etc. by various authors (e.g. McBride and Hebb, 1948; Kritzler, 

 1952 ; Wood, 1954). These clicks cover a wide band of frequencies, and may be 

 called at least "pale grey" if not actually "white". It is true that in our analyses 



