INDEX. 221 



are furnished with a gland behind containing a proper quan- 

 tity of oil ; to what purpose ; description of their feathers, 

 iv. 2, &c. The pectoral muscles of quadrupeds trifling to 

 those of birds; choose to rise against the wind, and why ; 

 all, except the nocturnal, have the head smaller, and less 

 in proportion to the body, than quadrupeds; their sight 

 exceeds most other animals, and excels in strength and 

 precision ; have no external ear standing out from the head ; 

 the feathers encompassing the ear-holes supply the defect 

 of the exterior ear ; the extreme delicacy of their sense of 

 hearing is easily proved by their readiness in learning tunes, 

 or repeating words, and the exactness of their pronuncia- 

 tion ; their delicacy in the sense of smelling ; instance of it 

 in ducks ; the tail guides their flight like a rudder, and as- 

 sists them either in the ascent or descent ; wonderful inter- 

 nal conformation ; the wind-pipe often makes many convo- 

 lutions within the body of the bird, and is then called the 

 labyrinth ; of what use these convolutions are, no naturalist 

 has been able to account ; this difference obtains in birds to 

 all appearance of the same species ; whence some derive 

 that loud and various modulation in their warblings is not 

 easily accounted for; birds have much louder voices, in 

 respect to their bulk, than animals of other kinds : all have 

 properly but one stomach, but different in different kinds ; 

 the organs of digestion in a manner reversed in birds ; why 

 they pick up sand, gravel, and other hard substances ; most 

 have two appendices or blind guts ; in quadrupeds always 

 found single ; all birds want a bladder for urine ; their urine 

 differs from that of other animals ; effects of the annual 

 moulting which birds suffer ; their moulting time artificially 

 accelerated, and how ; the manner in which nature performs 

 the operation of moulting ; their moulting season ; many 

 live with fidelity together for a length of time ; when one 

 dies the other shares the same fate soon after ; the male of 

 wild birds as happy in the young brood as the female ; no- 

 thing exceeds their patience while hatching ; Addison's ob- 

 servations to this purpose ; great care and industry in pro- 

 viding subsistence for their young ; they feed each of the 

 young in turn, and why ; perceiving their nests or young 

 to have been handled, they abandon the place by night, and 

 provide a more secure, though less commodious retreat ; the 

 young taught the art of providing for their subsistence ; 

 those hatched and sent out earliest in the season the most 

 strong and vigorous, 7 &c. They endeavour to produce 

 early in the spring, and why ; efforts for a progeny when 

 their nests are robbed ; such as would have laid but two- or 

 three eggs, if their eggs be stolen will lay ten or twelve ; 

 the greatest number remain in the districts where they have 

 been bred ; and are excited to migration only by fear, cli- 



