60 BIRDS OF LA PLATA 
on the mound. When Wenirsed or persecuted by 
other birds, they utter a peculiar cry, resembling 
the shrill neighing of a horse. In disposition they 
are most peaceable, and where they are abundant 
all other birds soon discover that they are not as 
other Hawks are and pay no attention to them. 
When soaring, which is their favourite pastime, the 
flight is singularly slow, the bird frequently remain- 
ing motionless for long intervals in one place; but 
the expanded tail is all the time twisted about in the 
most singular manner, moved from side to side, and 
turned up until its edge is nearly at a right angle 
with the plane of the body. These tail-movements 
appear to enable it to remain stationary in the air 
without the rapid vibratory wing-motions practised 
by Elanus leucurus and other hovering birds; and 
I should think that the vertebre of the tail must 
have been somewhat modified by such a habit. 
Concerning its breeding habits Mr. Gibson writes : 
“In the year 1873 I was so fortunate as to find a 
breeding colony in one of our largest and deepest 
swamps. There were probably twenty or thirty 
nests, placed a few yards apart, in the deepest and 
most lonely part of the whole ‘ cafiadon.’ They were 
slightly built platforms, supported on the rushes and 
two or three feet above the water, with the cup- 
shaped hollow lined with pieces of grass and water- 
rush. The eggs never exceeded three in a nest; the 
ground-colour generally bluish-white, blotched and 
clouded very irregularly with dull red-brown, the 
rufous tint sometimes being replaced with ash-grey.” 
