WILLOW- WARBLER, WOOD-WARBLER, CHIFFCHAFF 63 



If we admit the plausibility of the above explanation, the 

 puzzling fact yet remains that there is much old timber in this 

 country still awaiting its wood-wren or chiffchatf. It may be that 

 the birds, old and young, persist in returning each year to their 

 former haunts, and spread out from it only to the limits of timber 

 growth. If there is much timber near together, and close to it good 

 sites for nests, such as bracken, bushes, tufts of grass, then, as in 

 parts of N. Wales or Delamere Forest in Cheshire, the chiffchaff 

 or wood- wren, or both may be numerous. 1 If not, if around the 

 timber to which the birds return, and where they stay, there is a 

 wide tmtimbered space, then it is clear that a limit is at once 

 placed upon the numerical increase of the birds, the more so as 

 each pair insists upon exclusive possession of a given area. Thus 

 the unsuccessful pairs will find themselves with an inadequate food- 

 supply and will consequently be unable to breed offspring fit to 

 survive. This explanation may or may not prove to be correct. The 

 right explanation can be the result only of a close study of the facts, 

 and this has yet to be made. It is enough here to state the problem, 

 which is of considerable importance and interest, as it raises in a 

 particular form the general question as to why one species of a genus 

 is more successful than another. 



It is perhaps hardly necessary to add that the fact of its early 

 arrival is not likely to affect appreciably the relative numerical 

 position of the chiffchaff*. Though a certain number of individuals 

 arrive as early as the middle of March, and no doubt perish if a 

 spell of hard weather supervenes, yet the bulk do not reach us till 

 the end of this month and the early part of April, when large 

 numbers of willow- wrens are also making their appearance. The 

 wood-wrens, possibly the least numerous of the three, arrive last, the 

 first comers not being seen usually till mid- April, and the main body 

 till May. 



The males arrive from ten days to a fortnight before their mates, 



1 Coward, Fauna of Cheshire, vol. i. p. 141 ; Forrest, Fauna of N. Wales, pp. 94-5. 



