192 BIRDS OF LA PLATA 
constructed than is usual with the Tyrants. Soft 
materials are preferred, and in many cases the nests 
are composed almost exclusively of wool. The inside 
is cup-shaped, with a flat bottom, and is smooth 
and hard, the thistle-down with which it is lined 
being cemented with gum. The eggs are four, 
sharply pointed, light cream-colour, and spotted, 
chiefly at the large end, with chocolate. In the 
breeding-time these Tyrants attack other birds 
approaching the nest with great spirit, and have a 
particular hatred to the Carrion Hawk, pursuing it 
with the greatest violence through the air with angry 
notes, resembling in sound the whetting of a scythe, 
but uttered with great rapidity and emphasis. How 
greatly this species is imposed upon by the Cow- 
bird, notwithstanding its pugnacious temper, has 
already been seen in my account of that bird. 
The Scissor-tails have one remarkable habit ; 
they are not gregarious, but once every day, just 
before the sun sets, all the birds living near together 
rise to the tops of the trees, calling to one another 
with loud, excited chirps, and then mount upwards 
like rockets to a great height in the air; then, after 
whirling about for a few moments, they precipitate 
themselves downwards with the greatest violence, 
opening and shutting their tails during their wild 
zig-zag flight, and uttering a succession of sharp, 
grinding notes. After this curious performance they 
separate in pairs, and perching on the tree-tops each 
couple utters together its rattling castanet notes, 
after which the company breaks up. 
