ii8 ESSAYS OF A BIOLOGIST 



symbol. The other bird knows what is meant ; it 

 raises its head from beneath its wing, gives a sleepy, 

 barely discernible shake — and replaces the head. 

 In so doing it puts back the possibility of the cere- 

 mony and the thrill into its slumbers ; for it takes two 

 to make love, for Grebe as for human. The cock 

 swims off ; but he has a restless air, and in a minute 

 or so is back again, and the same series of events is 

 run through. This may be repeated three or four 

 times. 



If now another hen bird, unaccompanied by a mate, 

 reveals herself to the eye of the restless and disappointed 

 cock, he will make for her and try the same insinuating 

 informative head-shake on her 5 and, in the cases that 

 I have seen, she has responded, and a bout of shaking 

 has begun. Flirtation — illicit love, if you will ; for 

 the Grebe, during each breeding season at least, is 

 strictly monogamous, and the whole economics of its 

 family life, if I may use the expression, are based on 

 the co-operation of male and female in incubation 

 and the feeding and care of the young. On the other 

 hand, how natural and how human ! and how harm- 

 less — for there is no evidence that the pretty thrills 

 of the head-shaking display ever lead on to anything 

 more serious. 



But now observe. Every time that I have seen 

 such a flirtation start, it has always been interrupted. 

 The mate, so sleepy before, yet must have had one 

 eye open all the time. She is at once aroused to 



