338 BRITISH BIRDS. 



usually in September, shortly before the birds return to their winter 

 quarters, a second annual complete moult takes place in adult birds. The 

 autumn plumage is usually intermediate in colour between the spring 

 plumage and that of the bird of the year. 



The Sylviinee are, so far as is known, confined to the eastern hemisphere, 

 one species only having been known to cross Behring^s Straits into Alaska. 

 The Sylviinse might be again subdivided into three groups : — the migratory 

 Sylviinse, of which there are about ninety species, principally confined to 

 the Palsearctic Region, with the wings long, pointed, and flat, and the 

 first primary less than half the length of the second ; the non-migratory 

 Sylviinse, of which there are several hundred species, principally confined 

 to the iEthiopian and Oriental Regions, having rounded concave wings and 

 the first primary more than half the length of the second ; and, lastly, 

 the wide-billed Sylviinae, of which there are a hundred or more species, 

 inhabiting the tropical portions of the Old World, having, in addition to 

 the wide gape, the rictal bristles very largely developed, both characters 

 being of importance in assisting the birds to catch insects on the wing. 

 About a score species of the Sylviinse have been found in our islands, 

 belonging to five genera, the British examples of which may be distin- 

 guished as follows : — 



M. Asillaries yellow. 



«\ Bill slender, more or less dark underneath Phyiloscopus. 



6\ Bill stout, pale underneath Hypolais. 



h. Axillaries buff, white, grey, or brown. 



c'. Tail nearly even, or, if much graduated, longer than the wing Sylvia. 

 d' . Tail with the outside feathers considerably shorter than the 

 central ones ; never longer than the wing. 

 a^. Outside tail-feathers less than three fourths the length 



of the longest. No rictal bristles Locustella. 



i^ Outside tail-feathers more than three fourths the length 



of the longest. Rictal bristles moderately developed. Aceocephalus. 



Genus LOCUSTELLA. 



The Grasshopper Warblers were originally included by the earliest 

 writers who were acquainted with any of them in the comprehensive 

 genus Motacilla, and were afterwards removed from it into the genus 

 Sylvia with the rest of the Warblers. When the latter genus was broken 

 up, the Grasshopper Warblers were associated by the elder Naumann with 

 the Reed-Warblers in his genus Acrocephalus, in which Prof. Newton still 



