VISION OF BIRDS. 



529 



distance as they are said to do. We were led to scepticism on this sub- 

 ject, some twenty years ago, while observing- the concourse of birds of 

 prey from every point of the horizon, to a corpse floating down the river 

 Ganges, and that during the north-east monsoon, when the wind blew 

 steadily from one point of the compass for months in succession. It 

 was extremely difficult to imagine that the effluvia from a putrifying 

 body in the water, could emanate in direct opposition to the cur- 

 rent of air, and infringe on the olfactories of birds many miles dis- 

 tant. Such, however, were the dicta of natural history, and we could 

 only submit to the general opinion. We have no doubt, now that we 

 know the general opinion to be something wrong, that it was by means 

 of the optic rather than the olfactory nerve, that these birds found out 

 their quarry. 



The toucan ranks next to the vulture in discerning, whether by smell 

 or by sight, the carrion on which it feeds. The immense size of its 

 bill, which is many times larger than its head, was supposed to present, 

 in its honeycomb texture, an extensive prolongation of the olfactory 

 nerve, and thus to account for its power of smelling at great distances; 

 but, on accurate examination, the texture above-mentioned in the bill, 

 is found to be mere diploe to give strength to the bill. Now the eye of 

 this bird is somewhat larger than the whole brain ; and it has been 

 ascertained by direct experiments, that where any putrid carrion was 

 inclosed in a basket, from which effluvia could freely emanate, but which 

 concealed the offal from sight, it attracted no attention from vultures 

 and other birds of prey till it was exposed to their view, when they im- 

 mediately recognised their object, and others came rapidly from different 

 quarters of the horizon, where they were invisible a few minutes before. 

 This sudden appearance of birds of prey, from immense distances, and 

 in every direction, however the wind may blow, can only be accounted 

 for by their soaring to an altitude. In this situation their prey on the 

 ground is seen by them, however minute it may be, and their appear- 

 ance is merely their descent from high regions of the atmosphere to 

 within the scope of our optics. How far these remarks apply to the 

 raven, the only bird of the vulture genus that comes within our review, 

 we leave for more experienced naturalists."* 



M M 



