RED-BACKED ROCK-MARTIN 33 
Continent, and has a migration similar to that of 
many species of the Limicole 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. 
c I 
