MARSH WARBLER 



of which they defend against intruders ; they construct nests 

 so similar that if it were not for the fact that those of the 

 former are placed upon the ground and those of the latter 

 slightly above it they would be indistinguishable, but even this 

 slight difference does not appear to be absolute since the 

 Willow Warbler sometimes builds above the ground. They 

 make use of similar materials, frequently tearing off the bark 

 of the honeysuckle which they weave into the foundation of 

 their nests ; in the manner in which they feed their offspring 

 and clean the nest there is little or no difference, and their 

 behaviour after the young are able to fend for themselves is 

 identical. So it is with the Beed and Marsh Warblers. They 

 possess territories which they defend so long as the young 

 require their care ; their nests are similar in construction and 

 remarkable in type, the only difference being in the material 

 used — which is due to the fact that they do not live in a 

 similar environment — and in the manner in which they rear 

 their young there is no perceptible difference. Much the 

 same may be said of the Blackcap and Garden Warbler. Both 

 possess territories, defend them, and remain in them until the 

 young are fully fledged ; both build in similar situations and 

 construct nests which differ, if at all, but little, either as 

 regards type or material; and both adopt similar methods in 

 the care of their offspring. In the case of the two White- 

 throats the nests are placed in slightly different situations, 

 but beyond this the instincts connected with reproduction do 

 not differ. So here we have four separate examples in each 

 of which the reproductive instincts so nearly approach one 

 another that there is nothing to prevent our regarding the 

 species from this aspect as continuous forms. But besides 

 these special instincts there are those connected with migra- 

 tion and bodily sustenance, and they are uniformly alike 

 not only in those cases of close relationship, but practically 

 throughout the whole genus. The laws of migration which 

 apply to one apply to all, the same type of food is consumed, 

 and the methods adopted in securing it are alike. We have 



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