BRITISH WARBLERS 



are complete in themselves, and both birds are equally good 

 imitators of the songs of other species. Between these two 

 extremes there are a large number of notes uttered by different 

 species which are very similar, and may or may not be 

 imitations. I refer more especially to the call-notes, which, 

 being as a rule single notes, would the more easily be imitated, 

 and at the same time the more likely to be a natural produc- 

 tion. But when we consider the extraordinary number of 

 songs, call-notes, and combinations of sounds, produced by 

 bird life in general, we ought surely to be astonished, not 

 that we can occasionally detect a similar note in two different 

 species, but that we cannot more frequently do so. 



In the song of different individuals there is little variation, 

 nothing in fact to show that it reaches a higher degree of 

 perfection year by year, excepting perhaps that a greater 

 number of imitations may be remembered and reproduced. 



Their food consists principally of insects, Chironomiclce 

 and Limnobiidce being devoured in large quantities. But 

 Aphides may be said to form their staple diet, and these 

 they find clustering on the leaves of the reeds and on the 

 branches, twigs, and buds of the alders and willows surround- 

 ing the reed bed. It is always a difficulty to determine 

 exactly what the insects are which are being taken and 

 supplied to the young, since their digestive powers act so 

 rapidly. Even dissection of a young bird immediately after 

 the parent has supplied it with food is of little use, the 

 insects by that time being reduced to a pulp by the diges- 

 tive fluid, and consequently beyond recognition. This result 

 is not due to their being supplied with regurgitated food, for 

 one can see the insects being caught, carried, and delivered 

 even in a living condition into the throats of the young. 

 For the purpose of identifying the insects, I have from time 

 to time made a number of experiments, but hitherto with 

 •little success. Small pieces of cotton-wool placed in the 

 throat and secured with a fine thread prevented some of 

 them from being swallowed, if removed immediately the 



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