BIRDS AND BILHARZIAS1S. 395 



(3) The comparative scarcity of snails in the secluded portion 

 of the river is owing to the greater prevalence of wild birds in 

 those portions of the river. 



Granted for the sake of argument that wild birds occasionally 

 carry a few snail ova from pool to pool on their feet, this is nothing 

 in comparison to the vast numbers of snails they devour. It must 

 not be forgotten that every snail devoured by birds is the 

 potential parent of a small colony of snails. 



After twenty-five years' close observation, research and experi- 

 ment, I most emphatically assert that birds are not responsible for 

 the spreading of fresh-water snails; that, on the contrary, they are 

 Nature's chief euemies of snails; and in the degree that they are 

 persecuted, just in that degree will snails increase in numbers and 

 infest the rivers of South Africa. 



Apart from the evidence I have advanced in favour of birds 

 checking the multiplication of the snail, it has been demonstrated 

 in Baakens River by me, and elsewhere by Dr. Cawston and by 

 Dr. Porter, that tame ducks eliminate the snail. I claim that my 

 investigations prove that wild water birds do not spread the snail 

 pest by carrying the ova and young on their feet. This being so, 

 it is obvious that if tame ducks clear a pond of snails, wild ducks 

 and other snail-eating birds will do likewise if allowed to multiply. 

 Floods are, without question, the chief cause of the spread of 

 fresh-water snails, and wild water birds, fish, crabs and frogs are 

 Nature's checks. 



The small fresh-water fish common in the Baakens River and 

 known locally as the "Kurper," and to science as Spirobranchus 

 capensis, feeds voraciously on young snails. This fish is infinilelv 

 superior to "Millions" owing to its hardiness and capacity for 

 thriving under conditions fatal to Ihe great majority of other fish, 

 including "Millions." 



Having suffered for several years with bilharziasis in Natal 

 when a boy, I naturally have taken a lively interest in all that 

 bears on the disease, and in consequence of this special interest 

 my investigations were of as thorough a nature as I was capable 

 of making them. 



List of Birds which Prey on Fresh- Water Snails. 



White Stork ; Springhaans vogel ; Great Locust Bird 

 (Giconia alba). 



Black Stork {Giconia nigra). 



Marabou (Leptoptilus crumeniferus). 



Wood Ibis (Pseudotantalus ibis). 



Hammerkop; Paddevanger ; Mudlark {Scopus umbrella). 



Greater Flamingo (Phoenicopterus rose its). 



Lesser Flamingo (/' minor). 



All species of Geese and Ducks. 



All species of Rails, Crakes, Moorhens and Reed H'ms. 



Red-knobbed Coot (Fulica cristata). 



Peter's Fin-foot (Podica petersi). 



All species of Red Shanks, Green Shanks and Sandpipers. 



All species of Ruffs, Knots, Stints and Snipe. 

 7a 



