298 FIELD ZOOLOGY. 



a hen or a duck, and you will see this nictitating mem- 

 brane glide across the eyeball. 



Smell. 



As to the sense of smell, there is no such acuteness of 

 this sense as is found among the insects. This is the 

 sense of which the human family, also, is possessed in a 

 smaller degree than are many of the animals below man. 

 Some of the birds seem to possess the sense in a greater 

 degree than does man; but in the majority of birds, the 

 sense seems developed to about the same degree as in 

 our own case. 



The birds which have the keenest sense of smell are 

 the carrion-eating birds, vultures and buzzards. And 

 even these must be guided largely by the sense of sight in 

 finding their food. They would seem rather to sight their 

 food before they smell it. So far as their habits have been 

 observed, the birds are first seen circling high in the air 

 above the carcass, or they may be seen coming to earth 

 to observe whether some small animal they have sighted 

 is alive or dead. Though the animal may not have moved, 

 that sense is the sense through which the final judgment 

 is made in such a case; this seems undoubted. On the 

 side of the animal which is the object of the quest, the 

 conduct is even more puzzling. Being alive, it seems not 

 to fear the carrion bird, and does not run to cover ; but let 

 a hawk come near such an animal, and off it makes to the 

 nearest hiding place. 



The black vulture, which is about as tame in some 

 of our southern towns as our own domestic fowls, probably 

 uses smell more than sight in locating its food, since so 

 much of its time is spent on the ground. That a substance 

 may be perceived as a smell it is necessary, at least in 



