270 BULLETIN 133, UNITED STATES NATIONAL MUSEUM 



is somewhat deeper brownish gray, less whitish below than others 

 that have been noted thus far. Immature birds in ju venal plumage 

 lack the colored throat patch and have the breast and foreneck 

 rather faintly vermiculated with dusky. The throat patch is as- 

 sumed early in the post-juvenal molt, save in those birds that do not 

 develop it. Its lack in certain individuals is an apparent retention 

 of a character of immaturity, as it may be held that the throat patch 

 has been a secondary acquirement. A single adult female secured 

 at Formosa, Formosa, on August 24, while somewhat duller and 

 darker on the breast than the average, is matched closely by some 

 individuals in the considerable series at hand from the south, and is 

 similar to an old specimen in the United States National Museum 

 collection from Santa Fe. I have not seen S. s. a-ffinis Berlepsch 

 from Tucuman, but, on the basis of Berlepsch's original description, 

 consider the Formosan specimen nearer to fiavogularis. It is pos- 

 sible that the one taken at Formosa represents a northern migrant, 

 as it Avas shot in winter. 



Though recorded from northern Argentina, this spinetail was 

 most abundant in the semiarid regions of the south and west, where 

 it found a congenial home in low growths of bushes, particularly of 

 piquillin {Condalia lineata), atriplex, and a sort of grease wood 

 {Grahamia hracteafa) whose dense branches offered it safe cover. 

 In places, as near the coast at Bahia Blanca, the birds were abun- 

 dant and formed the dominant element among passerine species; at 

 other localities they were found sparingly or only in limited areas. 



As they clamber around among the thorny twigs of dense bushes 

 these spinetails seem rather clumsy in their movements, and when 

 touched by thorns often fall with seeming awkwardness to one side. 

 In reality, however, they are expert in progression, and, in spite of 

 their seeming lack of skill, are working rapidly and surely through 

 difficult passages. At intervals one may pause, often on a concealed 

 perch near the ground, to sing a low, double-noted trill, tsee-ee-ee-ee 

 tsee-ee-ee-ee, that is given by both males and females. Occasionally 

 one may come up to sing from a more pretentious perch on the top 

 of a bush where it has a wider view of its chosen world. The habit 

 of song among females seems common in this group as I have noted 

 it among others of related genera. Flight, tilting and fairly rapid, 

 is practiced for short distances only, as the birds drop into safe cover 

 as soon as possible. In addition to their song they uttered chattering 

 scolding calls, especially during the breeding season and were con- 

 siderably excited by squeaking. It was not unusual to see them on 

 the ground, particularly under heavy cover. 



A nest found near General Koca, on December 3, 1920, was placed 

 in a spiny bush among heavy branches about a meter from the 



