242 DISCOVERY REPORTS 



of high-frequency vibrations'.^ This again, especially at night, if they feed at night, would help them 

 to locate their prey. Fraser and Purves (1959) also call attention to the recent discovery that whales 

 use echo-location.- They write: ' The echo-location method consists of the transmission and reception 

 of an intermittent pulse with a variable recurrence frequency comparable with that used by bats. 

 There is evidence also that cetaceans can discriminate the quality of echoes with a high degree of 

 accuracy. Judged by the great development of the brain of these animals it would not be surprising 

 if it is found that they have a complete sound picture derived from purely auditory sensations'. 

 In effect, as Gray (1953) has remarked of bats, the whales 'have evolved a very efficient echo-sounding 

 equipment', and as Griffin (1955) more recently has said, its employment 'either to maintain orienta- 

 tion with respect to the bottom, surface, or large obstacles, or possibly to locate fish or other prey in 

 the water as bats appear to do in the air ', seems a distinct possibility. 



From the results of his recent experiments with bottle-nosed dolphins Kellogg (1958) concludes 

 that the ' location and discrimination of submerged objects by reflected sound signals is without doubt 

 a necessary and fundamental perceptual avenue for these cetaceans', and there seems every reason 

 therefore to believe, as Jonsgard (1959) has just written, that 'both the sounds which cetaceans 

 produce and their well-developed auditory organs play a large part in the welfare of this group of 

 animals '. 



Lillie, who originally described the wax plug in 1910, suggests that the 'whale probably receives 

 sound-vibrations by means of vibrating bony surfaces, after the manner of fishes ', the tympanic bulla, 

 fastened to the periotic bone by two thin pedicles, being a relatively dense and heavy sounding-box 

 that could easily be set in motion. 



In a recent review of sensory perception in the Cetacea Slijper (1961) concludes that it may well 

 be that 'whales and dolphins in search of food are attracted by the sound of their prey'. 



Hardy (1956) states that sometimes in the Antarctic, large swarms of krill show up in the dark as 

 phosphorescent patches in the water, adding that 'perhaps the whale is more easily able to find the 

 best feeding place when it is lit up like a restaurant ! ' I question however if the night swarms normally 

 light up the surface of the sea, personal observation over many years and a search through the litera- 

 ture suggesting that such a phenomenon, although it may happen, is far from common. I have never 

 seen the krill behave so myself nor have I heard mention of such behaviour by the whalers, and they 

 perhaps would be the most likely to know about it. Antarctic literature contains surprisingly few 

 references to night phosphorescence whatsoever, and fewer still, if indeed any, to massive displays 

 such as might be expected from large swarms of krill. The 'uncommonly white ' water (p. 40, note i) 

 reported by Cook in February 1775 could it is true have been caused by a luminescent krill patch^ 

 and so too perhaps could the 'gleaming' sea reported by Bellingshausen (1945) south of Kerguelen in 

 February 1820. Luminescence in the krill was observed by Murray (1895) in the 'Challenger' in 

 February 1874 and by Wilton (1908) in the ' Scotia' in February 1903, and they, so far as I am aware, 

 are the only observers (other than Hardy) to have recorded it. Murray writes, 'The above surface 

 organisms were collected by Mr Murray in a boat, Eiiphausia superba being especially abundant (the 

 supplementary eyes of which were in the evening observed to be phosphorescent) '. There is some 

 doubt however as to whether this refers to a natural display in the sea or to an exhibition of lumi- 

 nescence by a sample brought back alive on board. For if Murray was close enough to see it was the 



1 The whale's ear in fact is said to be so sensitive that it can even detect the ultrasonic beam emitted by the modern ' echo 

 whale-finder' (Crisp, 1954). It is interesting, therefore, to record that during recent survey operations by a Royal Naval 

 Ilydrographic unit in West Graham Land over-inquisitive killer whales were readily 'discouraged from taking an unhealthy 

 interest in the motor-boat' by switching on the echo-sounder (Wynne-Edwards, i960). 



- Klumov (1961) suggests that they come upon their food mainly by echo-location. 



^ It was sighted round about midnight, near Candlemas Island in the South Sandwich group. 



