APPEARANCE AT THE SURFACE i2i 



A similar though more remarkable change in the respiratory rhythm was obser\^ed (series B) in 

 a school of six or seven whales on 3 February. At 11. 15 hr. whales were sounding for long periods 

 (4-6 min.) and between whiles were blowing a few times at short intervals in apparent unison. 

 After many and tisually fruitless attempts had been made to approach them, at 12.15 hr. they suddenly 

 altered their behaviour in a stampede towards the south. They no longer remained below for long 

 periods and as we slowly overhauled them, hopes of marking rose. At 13.00 hr., however, their be- 

 haviour again changed. Their complacence returned and they sounded for lengthy periods. 



The rhythm demonstrated in Table i confirms the belief that individual behaviour may be studied 

 in collective behaviour, for their sounding together would be unlikely if the whales' actions were 

 unrelated. It may be helpful to compare the lengths of time the whales remained below water when 

 sounding (interval of sounding) and the interim periods during which breaths were taken (i.e. the 

 total of the periods occupied by successive intervals of blowing). The probability of being able to 

 distinguish an interval of sounding from an interval of blowing is likewise important. 



Two records of the latter already cited (B), were 115 and 140 sec. and they compared with sounding 

 periods of 3 min. 8 sec, 3 min. 35 sec, 4 min. 10 sec. and 4 min. 23 sec. These figures imply that 

 sometimes at least the sounding periods exceed the length of the interim periods. 



For the purposes of comparison, an arbitrary length of time may be chosen to distinguish between 

 the ' interval of sounding' and the ' interval of blowing'. On the basis of the data collected during the 

 observations of 19 December, according to which the whales blew several times during the course of 

 140 sec, an arbitrary limit of i min. is liberal as an allowance for the single ' blowing interval' and any 

 longer period of submergence may be regarded as a ' sounding interval '. When classified into intervals 

 of less than a minute and of more than a minute, and summed, the data (A) in Table 3 give the following 



Interval of blowing : Interval of sounding : : 64 min. : 103 min. 

 (<imin.) (>imin.) (38%) (62%) 



Over all the periods of observation, therefore, whales were ' sounding ', according to this empirical 

 definition, for 62 % of the time. The rhythm demonstrated in Table I suggests that, as often as not, 

 the respiratory needs of the animals were similar ; and although they did not always blow synchronously, 

 they chose the same periods to visit the surface and the same periods to sound. It follows that a pair 

 or school of whales may be expected to act in unison, in this sense, for at least 62 % of the time 

 (or more if the normal ' blowing interval ' is less than i min.). The timing data are therefore shown 

 not to be vitiated by whales blowing out of time. 



It became of interest to know whether the shorter and longer intervals were physiologically distinct 

 or whether they are merely length variants of the same process. If the latter we might expect the 

 longer and shorter intervals to merge and the intervals of medium length to be in the majority. The 

 frequencies of the observed intervals are given in Table 2, showing the greatest frequency among 

 the short intervals and a diminution with increasing length of interval. The figures suggest no obvious 

 discontinuity between the shorter and longer breaths but that the intervals of blowing merge 

 imperceptibly into intervals of sounding. If a distinction can be drawn between the two, the normal 

 limit of the former is likely to be between 40 and 50 sec. A curve made up of eight-second groupings 

 of the frequencies of the intervals of breathing is given in Fig. 3. The peak which shows at 50-54 sec. 

 suggests that this is a frequent and well-defined interval. Intervals of 24-28 sec. were frequently 

 found in the isolated observations (B). An interval of 18 sec. may represent a true interval of blowing, 

 but the intervals of shorter length almost certainly do not, for the manoeuvre of breaking surface 

 alone takes 4-7 sec. The shorter intervals are probably brought about by the overlapping of the 

 breathing intervals of diff"erent whales. 



