424 BRITISH BIRDS. 



flomed nest with the entrance at the side, a feature distinguishing them 

 from all the genera alluded to except Abrornis. Typical examples of the 

 Flycatcher Warblers have a very wide flat bill abundantly furnished 

 with long rictal bristles, and have rounded wings, with the first primary 

 half the length of the second, or nearly so. ]\Iany species, however, are 

 so exactly intermediate that, when I wrote the volume of the British- 

 Museum Catalogue of Birds containing the Sylviina, I should most 

 certainly have considered whether some of them ought not to be included 

 in the genus Phylloscopus, if my colleague for the time being had not cut 

 the Gordian knot for me by having already absorbed them into the volume 

 containing the Muscicapidoe. 



From the other allied genera, the various species of which build cup- 

 shaped nests, the yellow axillaries of the Willow-Warblers are a sufficient 

 distinction, with the exception of two aberrant species of the genus 

 Hypolais, which also have yellow axillaries. We must therefore find 

 another character, and are obliged to fall back upon the comparative size 

 of the bill and wing. The Tree-Warblers have large bills, the length of 

 the culmen being about a fifth of the length of the wing ; whilst the sub- 

 generic group of the Willow-Warblers, which, like the Tree- Warblers, 

 have no pale bar across the wings formed by the greater wing-coverts 

 having pale tips, have small bills, the length of the culmen being about 

 one sixth of the length of the wing. 



The "Willow-Warblers are essentially fly-catchers in their habits, and 

 may constantly be seen catching flies upon the wing ; but probably the 

 greater part of their food is picked ofii' the leaves. Accordingly their bills, 

 if not very wide, are considerably depressed at the base, and the rictal 

 bristles are well developed. Most of the species are migratory, the range 

 of their seasonal distribution frequentlj- extending over thousands of 

 miles ; consequently their wings are long, flat, and pointed, whilst the 

 bastard primary is very small. The migration of others is confined to the 

 plains within sight of the mountains where they breed. In these the wing 

 is shorter, more concaved to fit the body, and rounded, whilst the bastard 

 primary is larger, the vital energy required for its production not having 

 apparently been absorbed in lengthening the adjoining primaries. The 

 tail is generally even and frequently forked. All the species of the 

 genus are soberly coloured, the upper parts varying from yellowish 

 green to huffish brown, and the underparts from yellow to bufl' or 

 white. 



Probably all the species build a semi-domed nest on or near the ground, 

 and lay white eggs spotted with red. 



In their breeding-range the Willow- War biers are Palaearctic, ranging 

 from the Atlantic to the Pacific.' Several species extend their range 

 fuither north tlian the limit of forest-growth. Those species which do not 



