BRITISH WARBLERS 



the whole behaviour is so simply explained by selection, in 

 that those members that did not construct their nest 

 sufficiently securely would be very liable to lose their off- 

 spring, we may conclude that this is the means by which 

 the degree of adaptation has been attained. 



The nest is a delicate and beautiful structure composed 

 principally of the seed-heads of the common reed. The founda- 

 tion is formed of the leaves, or pieces of the outside of the 

 stem, of the dead common reed, intermingled with the thinner 

 stems of various rushes woven together with moss and wool, 

 and the interior of seed-heads and small stems of rushes, the 

 lining being entirely of the former. The external part is much 

 the same as the foundation, wool and moss being interwoven. 

 The manner in which the nest is actually woven to the stems 

 is remarkable, and I much regret never having seen the birds 

 at work "laying the first brick," so to speak, for to myself 

 it is a mystery exactly how the initial step is taken. The 

 most characteristic and at the same time most interesting part 

 about the nest is its great depth. Such a peculiarity cannot 

 but be for some purpose, and the reason often advanced is that 

 the eggs are thereby prevented from rolling out when the reeds 

 are bent. I have watched the nest swaying in a wind, and 

 have even bent the reeds for the purpose of finding out how far 

 it would have to be tilted before this would happen, and the 

 conclusion thus reached was that even if it were half an inch 

 shallower the wind would have to be of very exceptional 

 strength before it could bend the reeds sufficiently to bring 

 about such a result ; for it must not be forgotten that the nest 

 is not placed at the top of the reeds, but in the centre, three or 

 four feet from the water. If indeed it be true that there is a 

 danger of the eggs thus rolling out, what must we say as to 

 the young ? Herein, at least, lies a possible danger. Watch 

 them when a week or ten days old clinging to the nest, the 

 topmost birds level with or even slightly above the sides of the 

 nest, and then imagine the nest itself no deeper than that of 

 the Whitethroat, and the danger will be at once apparent. 



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