112 JOTTINGS ABOUT BIRDS. 



Bittern, and the signals of the Goatsucker. Again, 

 we find those birds that haunt dense thickets and 

 other close vegetation utter very clear and metallic 

 call-notes. We may mention the sharp note of the 

 Blackcap or the Whitethroat, resembling the striking 

 of two pebbles together, which instantly conveys 

 the bird's whereabouts to its mate or companions, 

 when the keenest powers of vision would fail to do 

 so. Nor must we fail to mention the various 

 distinct notes which are peculiar to one sex alone, 

 usually the male, which serve to indicate his presence 

 to the female ; the special cries of triumph which so 

 often celebrate the victory over a rival ; or the very 

 distinct note which conveys the approach of danger 

 to the gathered iiock, and wiiich is often well under- 

 stood by many stranger species, which profit by 

 the warning cry. What I wish to impress upon 

 the reader is the fact, the very obvious fact, that 

 all these varied notes have been undoubtedly pro- 

 duced, intensified, and differentiated through the 

 subde action of natural selection ; they are beneficial 

 acquirements, in some cases of absolutely vital im- 

 portance to a species. That they have also suffered 

 much modification by the isolation of individual 

 birds I am also bound to believe, although the data 

 bearing on this part of the question is so utterly 



