264 FIELD ZOOLOGY. 



known as preening their feathers after a water-bath. 

 This they do by pressing out a drop of oil from the oil 

 gland at the base of the tail, and rubbing it smoothly 

 over the feathers while drawing the feathers through the 

 bill. Aquatic birds, such as the domestic and wild ducks, 

 make special use of the advantages derived from this 

 process; as the oil renders the feathers less readily wet 

 by water. Grebes, which can remain long under water 

 in the act of diving and swimming, come out dry and 

 glistening, ready for another plunge, because of their oily 

 plumage. 



Fig. 104 — Tenuirostral bill of a nuthatch. 



Parrots use the bill in climbing. Some birds use the 

 bill as a weapon. But as an organ for securing food, the 

 bill has shapes as various as the food habits of the genera 

 of birds. It may have the form of a lever in one tribe of 

 birds, a pair of forceps, a hammer, a sieve, an awl, a hook, 

 or a knife in others. 



The Feet. 



Aquatic birds have lobed or webbed feet; or if the 

 bird lives in swampy places or wet grass land, the toes 

 are long and strong. In the Mexican and South American 

 jacanas, the toes are enormously lengthened, a provision 



