BRITISH WARBLERS 



the reeds, or rather a territory including reeds, are not avail- 

 able. When the opportunities of building in the willows fring- 

 ing the reeds, or in the reeds themselves, are equal, the latter 

 situation seems to be chosen in preference. I have examined a 

 number of nests for the purpose of discovering whether, in 

 their construction, new reeds were made use of more frequently 

 than old, and whether both new and old were utilised at the 

 same time ; for it occurred to me that, if the latter were the 

 case, the growth of the new reeds would cause the nest to 

 become tilted on one side, and bring about a calamity by 

 precipitating the young into the water. All three methods, 

 I find, are followed, although of the nests examined only one 

 was built upon both old and new reeds ; this, however, must 

 not be regarded as a correct proportion, the number examined 

 being much too small to enable such a proportion to be 

 correctly estimated. As a rule the nest is attached somewhat 

 loosely to the stems, and it might thus be able to slip and 

 automatically adjust itself to the growth ; but there are budding 

 leaves on the new stems, and an uneven surface and joints 

 on the old, which might at any moment prevent its slipping 

 and result in a gradual tilting of the nest to one side. There- 

 fore I am inclined to think that the danger is a real one, but 

 one that is kept in check by selection, and it would in no 

 way surprise me to find that the number of individuals that 

 constructed their nests after this fashion was but a small 

 proportion of the whole. Whether old reeds are used more 

 frequently than new is difficult to determine, since in many 

 places the natural conditions have been altered, the reeds 

 being cut in the winter months and the birds being conse- 

 quently forced to wait until the new ones have made sufficient 

 growth before commencing to breed. Neither is it possible 

 to say, or even to guess, what the original nest-building instinct 

 of the species was, whether, that is to say, the species as a 

 whole was limited to the use of new or of old reeds, or whether 

 some individuals used the one and some the other. The latter 

 alternative is not impossible, and there may be two races, so 



