BIRDS. 



81 



from a single locality in Fife, and he agrees with me as to the great 

 similarity in the spring note of the Cole-Tit. 



But apart from this similarity in the notes of two very different 

 species, as a test of its presence, the ChiffchafF must be considered 

 an irregular summer Wsitor, even where it has been well known to 

 nest. And this certainly appears to be the more evident towards the 

 northern limits of its range in this country in the breeding season. 

 Even where fairly well established, it seems to me to vary in 

 numbers, and even to disappear from its more advanced posts in 

 Scotland. In eflect, indeed, it seems to be of gi^eater delicacy of 

 constitution than some others of its congeners. In other words, 

 perhaps it possesses greater sensitiveness to changes of temperature, 

 and possibly other meteorological variations — a subject for inquiry 

 which, in my own belief, still requires more persistent and systematic 

 attention than has yet been devoted to it — whatever the outcome, 

 if any, may be — though I am well aware that there are some ex- 

 perienced ornithologists who do not believe in the amalgamation of 

 zoological with meteorological observations; or otherwise, attach 

 little importance to the influences of the latter. 



Phylloscopus trochilus (i.). Willow-Wren. 



The most abundant of all our summer Warblers over the whole area, 

 and universal in distribution even — as has often been before pointed 

 out — far up the hillsides, wherever a bit of green or even a single 

 birch-tree is found. Swarms by 21st April. In cold seasons there 

 is good reason to believe, such is the hardy nature of this little bird, 

 that temperature scarcely detains it on migration, though naturally 

 it is more silent and less conspicuous, and that too when the leaves 

 are not yet developed on the aspen or willow. Not gregarious. 



Just as we have a northern form of ChififchafF, so also we have a 

 northern form of Willow-Wren ; and their respective ranges in sub- 

 arctic countries have been fairly well worked out, the more arctic 

 form being also the more eastern form on the Continent in the case 

 of the Chiffchaff, though in the case of the Willow- Wren both forms 

 are found to intermingle in the areas of their distribution. 



Phylloscopus sibilatrix (BechsL). Wood-Wren. 



Fairly common, but not universally dispersed like the Willow- Wren. 

 Indeed, the Wood- Wren is more delicate, both in its choice and 

 in its necessities, and affects different kind of ground, or 

 rather foliage, than its congener, being especially fond of mixed 



F 



