266 BULLETIN 133, UNITED STATES NATIONAL MUSEUM 



represented, though two skins from Tucuman appear very slightly 

 darker than others. Birds in ju venal plumage have the tips of 

 breast, neck, and upper back feathers more or less faintly veraiicu- 

 lated with fuscous; the dark markings on the breast in some are 

 extended down on the abdomen and in others almost obsolete. 

 Young specimens are often more or less stained. The few taken in 

 Uruguay appear to have slightly larger bills than those from the 

 westward. An adult female taken January 29 is molting wing and 

 tail feathers while the body plumage is worn. 



In the present paper I have followed current usage in adopting 

 the generic term Sijitornis for a broad group of species that with- 

 out question may be divided into two or more restricted genera. 

 At this time only a little more than half of the species known in this 

 assemblage are available to me, sufficient to demonstrate that while 

 Mr. Cory's treatment of the group ^^ has certain merits, it is far from 

 conclusive, and in certain respects requires modification as regards 

 the allotment of species in the genera recognized. Further ma- 

 terial is needed before an intelligent discussion of the matter may 

 be made. 



The present species, one of more active habit than many of its 

 relatives, frequents groves and thickets often near the borders of 

 openings and clearings, wdiere it works about from 2 to 10 meters 

 or more from the ground. In ordinary circumstances the birds are 

 suggestive of titmice as they clamber and hop about among the 

 smaller limbs, and the long tail, with its pointed, rather stiffened 

 feathers, seems almost an encumbrance to their movements, as it is 

 often held in awkward positions. It may not be used even when the 

 bird swings around on the underside of a horizontal limb, so that 

 one comes to wonder at the possible function of the stiffened tip, 

 when suddenly one of the little birds may start up a tree trunk in 

 orthodox woodpecker fashion. Should any return be necessary they 

 are not averse to whirling around and sidling down head first as 

 acrobatically as any nuthatch, though this is not a usual habit. 



The birds are gregarious, and, in addition to traveling tw^o or 

 three together, have a predilection for association with other small 

 brush-haunting birds, and form in a way the guides for little 

 traveling companies of Thamnophilus gilvigaste7\ Picumnus, etc., 

 as chickadees do in similar bands in more northern regions. 



When excited /S. pyrrhophius comes about with rapid, sputtering 

 explosive call notes that may be represented as spee-ee-ee-ee or 

 tsee-ee-ee-a- In the breeding season they utter a low trill, not un- 

 pleasing in sound, that is suggestive of the song of Synallaxis f. 

 frontalis^ and is given from the cover of branches- 



ssproc. Biol. Soc. Washington, vol. 32, Sept. .30, 1919, pp. 149-160. 



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