142 BIRDS OF LA PLATA 



seek their food by preference on the bare level ground, 

 or where the vegetation is most scanty. This species 

 varies somewhat in habits, and seldom runs on the 

 ground, and chiefly inhabits the desert plains, where 

 the large grasses flourish. On one occasion when I 

 was with an expedition on the pampas for several 

 weeks, every day a number of these birds would 

 gather and follow us ; perched here and there on 

 the tall grasses with their bosoms towards us, they 

 often looked at a distance like large white flowers. 

 Old gauchos have told me that fifty years ago they 

 were abundant all over the pampas, but have disap- 

 peared wherever the giant grasses have been eaten 

 down and have given place to a different vegetation. 



Their note is a long, low whistle, the usual lan- 

 guage of the Tsenioptera ; but in this species it is 

 very like a human whistle, on account of which the 

 bird is named Boyero (ox-driver) on the pampas. 

 One severe winter great numbers of them appeared 

 in the neighbourhood of Buenos Ayres, and it was 

 amusing to see the dogs thrown into a great state of 

 excitement by the low whistling notes heard per- 

 petually from all sides. Every few moments they 

 would start up and stare about them to ascertain 

 where the deceptive call came from, and in spite of 

 many disappointments they would occasionally all 

 rush away, loudly barking, into the plantation, 

 convinced that some person there was whistling to 

 call them. 



The Black-Crown makes a somewhat shallow nest 

 in a bush or large clump of grass, and lays four 



