170 BULLETIN 196, UNITED STATES NATIONAL MUSEUM 



produce more music than any other species of the woodland. I am 

 not familiar with this thrush on its nesting ground; but it seems that, 

 although it sings so much here, it is always in an undertone, as while 

 passing northward through the middle tier of the United States later 

 in the spring. While earlier in the year they have been confined to the 

 forest and its edges, these birds are now often seen in the bushy clear- 

 ings, in hedgerows, and sometimes even in cultivated fields. At times 

 in April, riding along the grassy cartroads of El General, I have heard 

 the song and the fluid quit arising from every little patch of woodland 

 that skirted the road. At this season one individual frequently pur- 

 sues another; apparently their instinct to defend a territory begins to 

 awaken while they are still so far from their summer home. 



"While usually these so numerous birds are rather evenly dis- 

 tributed, with little tendency to flock, at sunrise on April 14, 1940, 

 while watching great clouds of northward-bound swallows pass over 

 the open crest of a hill, I saw about eight russet-backed thrushes to- 

 gether at the edge of a small tract of woodland, beside the open pasture. 

 They created the impression of a migrating flock just come down to 

 rest and forage. 



"Late in April or the first days of May, while still to all appearances 

 as numerous as ever, the russet-backed thrushes sing much less than 

 at a slightly earlier date. I can explain this falling off of song, noted 

 in several years, only by the hypothesis that the males depart first, 

 leaving a preponderance of females that do not sing. With most other 

 migrant song birds, the males that linger latest are the most songful at 

 the time of their departure. 



"Although the russet-backed thrush arrives late in El General, it 

 also lingers late. My earliest"date for its arrival is October 18, 1936. 

 My last spring records are : May 10, 1936; May 4, 1937; May 11, 1939; 

 April 21, 1940; and April 30, 1942. I have'never seen the species any- 

 where on the Caribbean slope of Central America except late in spring, 

 when migration was in progress. My actual records are: Barro Colo- 

 rado Island, Canal Zone, April 4, 5, and 6, 1935; Vara Blanca, Costa 

 Rica, 5,500 feet, April 3 to May 7, 1938; and Pejivalle, Costa Rica, 

 2,000 feet, April 15, 1941. During the year I spent on the Sierra de 

 Tecpan in west-central Guatemala, studying the bird life between 

 7,000 and 10,000 feet, I recorded this species only on April 12 and 

 October 19 and 20, 1933. I have not attempted to distinguish the 

 races of Hylocichla ustulata in the field ; but according to the analysis 

 of Griscom (Bird Life in Guatemala, 1932) the birds wintering on the 

 Pacific slope would all belong to the race ustulata, while the transients 

 recorded on the Caribbean slope might be either this race or 

 swainsoni." 



