GENERAL HABITS 193 



Thrushes, Wrens, Vireos, and Bulbuls we find 

 bills adapted not only for picking up insects, 

 but for seizing worms, grubs, and so forth ; 

 then as we come to the more specially insec- 

 tivorous forms we find a widening of the bill 

 and a greater development of rictal bristles, as 

 in the Flycatchers ; whilst in the exclusively 

 insectivorous feeders the bill itself becomes 

 small and weak and the gape exceptionally 

 wide, as in the Swallows. Another change of 

 food is unerringly indicated as we reach the 

 Titmice and Nuthatches, the bill now being 

 perceptibly and relatively stouter, and adapted 

 for digging into wood and other hard sub- 

 stances in quest of grubs, nuts, and so on ; 

 whilst still greater strength and a perceptible 

 hook and notch characterise the bill of the 

 Shrikes, which seize large case-protected insects, 

 small birds and mammals. Then we revert 

 to the finer-shaped bills again as we reach 

 the insectivorous Wagtails, for instance, whilst 

 a more slender and longer bill again is pre- 

 sented by the Sun-Birds, many of which have 

 this organ specially modified in shape and 

 length to reach insects, and possibly nectar, 

 in certain flowers. Another change of food 

 introduces us to yet another type of bill. With 



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