AQUATIC WARBLER ON MIGRATION. 87 



middle line of the crown from beak to occiput, the medial buff 

 line. In the Aquatic Warbler this is very broad and clear 

 yellow-buff in colour. In the immature Sedge-Warbler it is 

 narrow and duller in shade ; in the adult Sedge-Warbler it is 

 much duller, and varies from dark buff to dusky brown. On either 

 side of the medial buff line are two dark streaks. These may 

 be called the inner da?°k lines. In the Aquatic Warbler they are 

 clearer, darker, of a warmer hue, and broader than in the 

 Sedge- Warbler. On either side of these are two light streaks. 

 These may be called the outer buff lines. In the Aquatic 

 Warbler they are exceedingly thin, though of the same colour as 

 the medial buff line. In the Sedge- Warbler they are of nearly 

 equal breadth with the medial buff line and of the same colour. 

 On either side of the outer buf lines are two dark streaks which 

 may be called the outer dark lines. Though darker and richer 

 in colour in the Aquatic Warbler, they are of about equal thick- 

 ness in both species. They lie immediately above the buff 

 superciliary stripe, which is well-marked in both species and 

 calls for no further notice. 



Seeing, then, that there is an interesting inter-relation 

 in the plumage pattern of the head in the two species — a 

 pattern consisting essentially of alternating longitudinal buff 

 and blackish streaks — and that the points of distinction 

 are relative and not absolute, variations are not to be 

 altogether unexpected. In a large series of Sedge- Warblers 

 which I have examined, I have found gradations not only in the 

 shade but in the relative thickness of the buff streaks, leading 

 from the typical head plumage-pattern of the Sedge-Warbler 

 to forms resembling that of the Aquatic Warbler (vide fig. 4). 

 And, no doubt, if one could in the same manner go through 

 as large a series of specimens of Aquatic Warblers, one would 

 find variations approaching the head plumage-pattern of the 

 Sedge-Warbler. The above remarks apply in the main to 

 immature birds as they appear in autumn garb, at which 

 season the buff in the head of the Sedge-Warbler is much 

 lighter than in spring. If in the nuptial plumage a variety of 

 Sedge- Warbler were found, in which the medial head streak was 

 broader than usual, resembling in that respect the same streak 

 in the head of the Aquatic Warbler, still, owing to the fact that 



