1916 J ii.vii.i.EY, Bird-watching and Biological Science. 149 



takes place. At the same time nest-building starts, and very 

 shortly the eggs begin to be laid ; and then follow in turn the period 

 of incubation and the period when the young are still unfledged 

 and must be constantly fed. Then the nest is left, and a period of 

 family association starts, during which the fledged young are being 

 taught to find their own food and fend for themselves. This 

 family life may break up very soon (e. g. in August; the English 

 Robin) or may last right on through the winter until the next 

 pairing-season (many Paridse). 



Most of this is common knowledge. Recent work, however, is 

 extending our knowledge in two ways. First, it is becoming clear 

 that in many species pairing-up is even earlier than was supposed, 

 sometimes even in November or December, and also that in a good 

 many species which were supposed to pair for the season only, 

 the union is really for life, the pair preserving its identity through 

 the winter, sometimes even when flocks are formed.^ 



In the second place, we are beginning to understand the relation 

 of the so-called "Courtship-actions" — ^ the displays and dances 

 and songs — to the annual history. For example; there is often 

 no display at all previous to the period of pairing-up; then — most 

 interesting point of all — there may be a long period when " Court- 

 ship" (in the sense of active display by one or both sexes) may be 

 very much in evidence, although the birds have already paired-up 

 into couples, but coition has not yet taken place. 



However, I think that it will be as well to look at some concrete 

 examples of the various sorts of sex-relationship found in birds. I 

 will take three, all more or less non-typical, to illustrate the great 

 variety that exists in this matter of courtship. 



I make no apology for beginning with a life-history which I have 

 myself investigated — that of the great Crested Grebe ^ — for here 

 I am sure of every fact. 



In this aquatic species the two sexes are almost identical. Both 

 are adorned with a beautiful crest, composed of two black ear-tufts 

 and a ruff of chestnut, black, and pure white; this crest is very 

 slightly less developed in the hen than in the cock, but is used 

 exclusively in courtship, and used equally by both sexes. 



1 e. g. the Dabchick (Podiceps fluvialilis) . as reported by Mr. Mottram in a letter to me. 

 "Huxley ('14). 



