SOCIABLE MARSH-HAWK 59 
so that the whole shell is red. The shell is polished 
and exceedingly fragile, a rare thing in the eggs of a 
Raptor. 
An approach to the nest is always greeted by the 
birds with long distressful cries, and this cry is also 
uttered in the love-season, when the males often 
fight and pursue each other in the air, The old and 
young birds usually live together until the follow- 
ing spring. 
SOCIABLE MARSH-HAWK 
Rostrohamus sociabilis 
Deep slatey grey; wing feathers black; rump white; tail white 
with a broad grey band ; eyes crimson, bill and feet orange; length 
17, wing 13 inches. Female similar but larger. 
Tuis Hawk in size and manner of flight resembles 
a Buzzard, but in its habits and the form of its slender 
and very sharply hooked beak it differs widely from 
that bird. The name of Sociable Marsh-Hawk, 
which Azara gave to this species, is very appropriate, 
for they invariably live in flocks of from twenty to 
a hundred individuals, and migrate and even breed 
in company. In Buenos Ayres they appear in Sep- 
tember and resort to marshes and streams abounding 
in large water-snails (Ampullaria), on which they 
feed exclusively. Each bird has a favourite perch 
or spot of ground to which it carries every snail it 
captures, and after skilfully extracting the animal 
with its curiously modified beak, it drops the shell 
