RED-BACKED ROCK-MARTIN 33 



Continent, and has a migration similar to that of 

 many species of the Limicolse order. Thus, flying 

 south in the autumn of the northern hemisphere, it 

 crosses the tropics and extends its enormous journey 

 to the southernmost parts of South America. On 

 the Rio Negro, in Patagonia, I did not meet with 

 it, and suppose its summer resort must be south 

 of that locality ; and, judging from the immense 

 numbers visible in some seasons, I should think 

 that they must, in their non-breeding ground in 

 Patagonia, occupy a very extensive area. They 

 do not seem to be as regular in their movements 

 as other Swallows here ; some years I have observed 

 them passing singly or in small parties during the 

 entire hot season : usually they begin to appear, 

 flying north, in February ; but in some years not 

 until after the middle of March. They are not seen 

 passing with a rapid flight in close flocks, but straggle 

 about, hawking after flies ; first one bird passing, 

 then two or three, and a minute or two later half 

 a dozen, and so on for a greater part of the day. So 

 long as the weather continues warm they journey in 

 this leisurely manner ; but I have known them to 

 continue passing till April, after all the summer 

 migrants had left us, and these late birds flew by with 

 great speed in small close flocks, directly north, as if 

 their flight had been guided by the magnetic needle. 

 While flying this species continually utters sharp 

 twitterings and grinding and squealing notes of 

 various lengths. 



