BRITISH WARBLERS 



in securing the nest to the supports. At the same time this 

 method in the case of the Marsh Warbler is subject to a 

 variation which is referred to by Mr. Warde Fowler as basket- 

 handles, the nest having thereby the appearance of being- 

 slung from the supports, since the dead grass which actually 

 forms the sling is slightly above the top of the nest; but 

 it is by no means always adopted. The nest is frequently 

 placed in a fork from which rise four or five perpendicular 

 stems, and although it would clearly be secure without any 

 actual attachment to the stems, yet the bird takes infinite 

 pains to weave the grass round the supports after the manner 

 adopted by the Eeecl Warbler. Now some of these special 

 features in the construction of the nest are of considerable 

 importance when we bear in mind the nature of the environ- 

 ment and the peculiarly close relationship of the bird to the 

 Beed Warbler. In my description of the latter species I 

 gave my reasons for believing that the depth of the nest was 

 a factor of no small importance for the welfare of the species, 

 since thereby the young — not the eggs as is sometimes 

 suggested — were prevented from being precipitated into the 

 water. I further stated my ground for the belief that we need 

 have no hesitation in attributing the development of this 

 peculiarity to natural selection, nor in regarding the regularity 

 in this type of structure as the outcome of the same principle. 

 A.s to whether the depth is to ensure the safety of the young 

 or of the eggs opinions may differ, but no one can well dispute 

 the fact that one or the other must be the cause of the 

 development, and for our present purpose that is sufficient. 

 What then does an examination of the nests of the Marsh 

 Warbler reveal ? It reveals all the peculiarities of those of 

 the Eeed Warbler — complete adaptations to a special environ- 

 ment — but with this difference that the constancy of type has 

 been replaced by variation, the adaptive characteristics of the 

 structure being in a condition of instability. But when we 

 here speak of the adaptive characteristics, we manifestly make 

 use of a wrong term, since they are not adapted to the 



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