BRITISH WARBLERS 



of arrival of the females is often the cause of much quarrelling ; 

 for although she seems to pair with the owner of the territory 

 in which she first makes an appearance, yet throughout the 

 first morning or the first day of her arrival she does not 

 confine herself so strictly to the boundaries as she is wont to 

 do later on. It is clearly impossible for her to know the limits 

 of the territory in which she has settled ; she must learn by 

 experience ; and this experience is probably gained under 

 compulsion, for a male can sometimes be seen pursuing a female, 

 who has crossed the boundary, and driving her back again into 

 his territory. Her arrival in a territory is the cause of extreme 

 sexual excitement on the part of the male who is its owner, 

 and, if she crosses the boundary, on the part of the adjoining 

 male. This excitement expresses itself similarly in both 

 sexes, and results in much pursuing and frequent mock con- 

 flicts. During the pursuit the flight is often rapid, the birds 

 twist and dart in and out of the bushes, momentarily settling, 

 but only to commence their round again. These outbursts of 

 excitement are by no means continuous, but spasmodic, and 

 may be commenced by one sex or the other. Thus the female 

 at one moment appears to call the male by singing, when he 

 either approaches her slowly, or flies at her more abruptly, 

 uttering at the same time a quiet purring sound. This act of 

 flying at her is of common occurrence, and when it takes place 

 she may on his approach spread her tail, assuming an attitude 

 of defence which results in a fluttering of tiny wings and a 

 momentary clicking of bills. Or he may fly towards her 

 apparently with the object of presenting her with food — an 

 attention on the part of the male which is common amongst 

 many species — and he then warbles quietly or rather sings his 

 song continuously. When the male overtakes her during the 

 pursuit, both birds may fall fluttering to the ground in their 

 excitement. 



The manner in which sexual emotion is expressed varies 

 in different, and even in closely allied, species. Why it should 

 be so we cannot tell ; yet the difference is often striking. I 



16 



