FEEDING-HABITS OF THE DUNLIN. 



13 



the bill was opened up to its base. On the second occasion the 

 bill was sometimes opened and sometimes closed during the 

 downstrokes, but I suspect that the apparent closure was due 

 to my inability to see a trifling separation of the mandibles 

 towards the tip of the bill. Though the shallow probings are 

 not always septate, formation of the delicate septa may be pre- 

 vented by various causes, and in default of a septum it is 

 seldom that a semilunar ridge cannot be found across the 

 floor of each probing. The present view gains support from 

 observation of the actions of waders which are larger and 

 slower than the Dunlin ; septa occur, to my knowledge, in 

 the shallow probings of the Lapwing, Snipe, Common Sand- 

 piper, and Redshank, and the method attains its greatest 

 development in Starlings and Rooks, which often test the 

 ground with the tips of the mandibles separated as widely as 

 they can be. 



So there is evidence for the belief that the mandibles are 

 separated during search, and that the separation increases as 

 the bill goes deeper, but they remain nearly parallel until the 

 bottom of the deep probing is reached, when, as a writer 

 has suggested,* the terminal part of the upper mandible is 

 expanded in contact with the capture — a movement which ap- 

 pears to be reflected in the form of the deep probing. The 

 partial separation of the mandibles makes introduction of the 

 bill more easy, it increases the tactile area, and may, by com- 

 parison between the two points of contact, afford a clearer idea 

 of the form and consistence of hidden objects. One advantage 

 of the extensile mechanism lies in the fact that the minimum 

 quantity of sand has to be pushed aside,! though I am unable 

 to agree with Mr. Workman in supposing that the bill is closed 

 during introduction, to prevent the mouth from being filled with 

 dirt. The existence of septa in the shallow probings seems to me 

 to prove that the open bill can be driven into and out of the 

 ground without being soiled, but when the bird makes a capture 

 it has to swallow the material of which the septum is composed. 

 In this way I account for the large quantity of extraneous 

 matter, sand, mud, rootlets, and the like, which is found in the 



* Pycraft, 'Ibis,' 1893, p. 361. 

 f Workman, « Ibis,' 1907, p. 614. 



