1911] Swarth: Alaska Expedition of 1909. 103 



land all along the stream, and he shot a yellowthroat at the 

 farthest point he reached. 



We find here an extraordinary instance of a bird race from 

 the arid interior which has invaded a region of extreme humidity 

 through narrow passes, and which has undergone no modification 

 in its coloration in the direction of melanism. 



Wilsonia piisilla pileolata (Pallas). Pileolated Warbler. 



By no means as generally distributed as I had expected to 

 find it, and not seen on any of the more western islands of the 

 archipelago. First noted at Portage Cove, Revillagigedo Island, 

 June 28 to July 4, where several were observed in thickets 

 bordering the meadows. The males were in full song at this 

 time, and making themselves so conspicuous thereby that I 

 could hardly have overlooked the species had it been present at 

 any of the points previously visited. It was next encountered at 

 ]\Iitkof Island, evidently migrating, and fairly common in the 

 alders along the beach. At Thomas Bay and Port Snettisham 

 also it was quite abundant at times, and on the Taku River it 

 was frequently observed during the early part of September. 

 By the middle of the month the birds were practically all gone, 

 though a belated straggler was seen as late as September 21. 



Eleven specimens were secured : two adult males from Revilla- 

 gigedo Island (nos. 9482, 9483), a juvenal male from Mitkof 

 Island (no. 9484), and eight immatures from Mitkof Island, 

 Thomas Bay, and Port Snettisham (nos. 9485-9492). No. 9484 

 (male juvenal August 4) is molting from juvenal to first winter 

 plumage, with the former predominating. It has no trace of 

 the black cap, the pileum being concolor with the back, though 

 the forehead is decidedly yellowish. The greater wing coverts 

 are distinctly tipped with whitish, forming a conspicuous bar 

 across the wing. The immature males in first winter plumage 

 have the black cap quite as extensive and distinct as the adults 

 though the black feathers are more or less tipped with yellowish, 

 l)ut in the immature females such marking is either entirely 

 absent or indicated by but one or two black feathers. 



