BRITISH WARBLERS 



Why should males be so strongly impelled to reach their 

 breeding grounds ? An answer to this question is, I believe, 

 to be found in the necessity for occupying a breeding territory. 

 Each male, that is to say, must secure a position wherein the 

 rearing of its offspring can be safely accomplished, and this 

 is the first and most important step towards reproduction. 

 I must explain what is meant by a "breeding territory." 

 Let us suppose that we watch a male of one of our common 

 species — a Eeed Bunting for instance — and accurately record 

 its movements each day during the first few hours of day- 

 light from about the second week in February, what do 

 we find? Not that its behaviour is of a casual description, 

 not that it is here to-day and gone to-morrow, but that 

 all its movements are subject to a routine which becomes 

 increasingly definite as the season advances. There it is 

 in the same plot of ground, in the same bush or clump of 

 bushes, taking short flights first in one direction and then 

 in another, attacking other males that come within a certain 

 radius and exhibiting in all its actions a strong disposition to 

 make its own just that one particular corner of the universe. 

 Those few acres wherein it performs this routine of activities 

 and awaits a female I have termed a breeding territory, the 

 dimensions of which vary, according to the species and 

 according to the environment, from the few square miles 

 of the larger birds of prey, to the few square inches on a 

 ledge of rock which is all that the Guillemot requires. I 

 have, perhaps, in the earlier parts of this work, expressed 

 myself unguardedly when speaking of boundaries, and 

 the critic is perfectly justified in taking me to task for 

 seeming to imply a definiteness which does not really exist. 

 In the history of the Marsh Warbler I therefore tried to 

 make it clear that the word should be interpreted some- 

 what liberally. The conception of a boundary must not be 

 that of a line definitely delimiting an area the exact extent of 

 which the bird is cognisant of, but of the normal extent of 

 range which has become habitual and has, I suppose, been 



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