1927] Pilsbry-Bequeart, The Aquatic Mollusks of the Belgian Congo 930 
Bechstein), water-rail (Rallus aquaticus Linneeus), heron (Ardea cinerea 
Linneus), etc., prey extensively upon them in Europe. The heron will 
even fish up Anodonta and fly into a tree, breaking the shell against the 
branches. It is claimed that the hooded and carrion crow (Corvus cornix 
Linnzeus and C. corone Linnzus) also feed upon this mussel, carrying 
them to a considerable height to let them drop on the ground and thus 
easily reaching the animal in the broken shell. Domestic ducks are such 
efficient snail-hunters that they may clean out a pool in a surprisingly 
short time. Cawston has called attention to the practical absence of 
snails near Port Elizabeth, South Africa, in ponds where domestic ducks 
were kept, these birds thus being very helpful in the control of blood- 
flukes (see p. 96). The white-headed stilt of Australia, Hamantopus 
leucocephalus Gould, was found by Cleland to include species of Bulinus 
in its diet.1 | . 
It is generally known that the snail-hawk or everglade kite, Rost- 
rhamus sociabilis (Vieillot), of tropical and subtropical America, feeds 
exclusively upon aquatic snails mainly of the genus Pomacea. The 
lengthened, excessively acute claws are well adapted to catching hold of 
the slippery, smooth shell, while the upper bill forms a strongly arched, 
nearly circular hook on which the snail can be spiked. H. Lang’ has 
recently described how this bird manages to extract the mollusk from the 
shell. At Georgetown, British Guiana, Rostrhamus mainly gathers 
Pomacea dolioides (Reeve), which it secures in the claws of one foot. | 
‘The hawks then perch on one foot and with the other quietly hold the 
snail in such a manner that it can emerge from the shell. The birds make 
no attempt whatever to extract it by force, but watch for the voluntary 
extension of the animal beyond the aperture of the shell. With that 
propitious moment comes the next step in the drama. Quick as a flash 
the hawk’s bill pierces the snail apparently back of the operculum. It 
happens so rapidly that one is not able to clearly follow the operation. 
Asa further step the snail, now spiked upon the beak, is instantly pushed 
up to the middle of the upper bill from which it stands off like a bump as 
big as a large walnut. Then begins a second wait. Gradually the 
mollusk’s muscles relax. A few minutes later the snail-hawk vigorously 
shakes its head and before even the light, empty shell has reached the 
erassy ground Rostrhamus has swallowed its victim, operculum and all.’’ 
The extent of the depredations of Rostrhamus upon the snail colonies may 
be judged from the fact that over 2.000 empty shells were obtained below 
1 j Bull. No. 15, Dept. Agric. New South Wales, p. 46. ie 
fo a Oe ert and Rostrhamus at Georgetown, British Guiana.’ The Nautilus, 
XX XVII, pe: 13-707 ae 
