214 BIRDS OF LA PLATA 
place is forsaken, the whdfe concourse leaving in a 
body, or scattering in all directions over the sur- 
rounding country ; and until the following summer 
their movements depend entirely on food and water. 
If the weather is dry the Gulls disappear altogether ; 
and if grasshoppers become abundant the country 
people wish for rain to bring the Gulls. When it 
rains then the birds quickly appear, literally from the 
clouds, and often in such numbers as to free the 
earth from the plague of devastating insects. It is a 
fine and welcome sight to see a white cloud of birds 
settle on the afflicted district ; and at such times their 
mode of proceeding is so regular that the flock well 
deserves the appellation of an army. They sweep 
down with a swift, graceful flight and settle on the 
earth with loud, joyful cries, but do not abandon 
the order of attack when the work of devouring has 
begun. The flock often presents a front of over a 
thousand feet, with a depth of sixty or seventy feet ; 
all along this line of battle the excited cries of the 
birds produce a loud, continuous noise; all the birds 
are incessantly on the move, some skimming along 
the surface with expanded wings, others pursuing 
the fugitives through the air, while all the time the 
hindmost birds are flying over the flock to alight in 
the front ranks, so that the whole body is steadily 
advancing, devouring the grasshoppers as it pro- 
ceeds. When they first arrive they seem ravenously 
hungry, and after gorging themselves they fly to 
the water, where after drinking they cast up their 
food and then go back to renew the battle. 
