152 THE MIGRATIONS OF BIRDS 



zags across openings in the forest; a kingbird {Ty- 

 rannus m. melancholicus) appears and continues 

 south into the scantily wooded area of central Ar- 

 gentina; and a little goatsucker {Setopagis parvulus) 

 arrives from winter quarters in Bolivia and Brazil, 

 to utter its tremulous calls at evening. 



The low woodland of the level reaches of the in- 

 terior Chaco, which lies west of the Rios Parana and 

 Paraguay, from Santa Fe in Argentina to southern 

 Bolivia, with its dense jungles impervious to cold 

 winds, and its tangled openings where the rays of 

 the sun are warm even on frosty mornings, harbors 

 many winter visitants from the more open country, 

 or from the mountain slopes to the west. Here 

 small flycatchers, warblers, and other insect-eating 

 birds rest in comfort, remaining quiet during brief 

 spells of cold, and becoming active when the sun 

 appears. Broad stretches of dense scrub that cover 

 the low hills east of the mountains from Tucuman 

 northward, also offer secure coverts where small 

 birds at times fairly swarm. 



Altitudinal migration is easily evident in the 

 Andean foothills from Bolivia southward, as in 

 autumn flycatchers and other small birds work down 

 the mountain slopes in little bands which travel 

 down to the plains and then pass on northward. 

 With heavy storms at high altitudes these move- 

 ments are especiallv marked and may include birds 



