40 BIRD BEHAVIOUR 



and very helpless creatures. Like Ducks, they eat 

 both animal and vegetable food, and in captivity 

 eat and thrive on such an unnatural diet as grain. 

 In both Ducks and Flamingoes the sifting apparatus 

 is found along the edges of both jaws, but in some 

 of the Petrels there is found a similar structure for 

 extracting food suspended in water which still more 

 recalls that of the whalebone whales, in which the 

 so-called " bone " (which is really horn) is confined 

 to the upper jaw, by being similarly limited to the 

 upper bill. 



These Petrels, called Whale-birds by sailors, 

 belong to the genus Prion of naturalists ; they are 

 small birds about as big as Doves, of a pigeon-blue 

 colour, and display a beautiful gradation from a 

 bill which is quite ordinary except for the ridges 

 visible in it when opened to one which is so bulged 

 out at the sides, and has such long fringes, that the 

 caricature of a whale's head is at once obvious. 

 Yet the species are so closely related that it is quite 

 difficult to separate them, so that here is evidently 

 a case where evolution is comparatively recent and 

 has not resulted in any decided differentiation. 



To return to the subject of mollusc-eating birds, 

 from which we have been led by the consideration 

 of these fringed-billed birds, whose " dentition," if 

 we may use the expression, is just as worthy of study 

 as the true teeth of beasts or reptiles ; we find in 

 the Oyster-Catchers (Hamatofus) which, some pied 

 like our own, and some black, haunt sea-coasts 

 nearly everywhere, a special weapon for getting to 



