Faculties of Vision in Birds 93 



Our birds'-eye views, of which the accurate execution 

 is so tedious and difficult, give but a very imperfect picture 

 of the relative inequality of the surfaces which they repre- 

 sent, but birds can choose the proper stations, can succes- 

 sively traverse a field in all directions, and with one glance 

 comprehend the whole. On the other hand, the quad- 

 ruped knows only the spot where it feeds — its valley, its 

 mountain, or its plain ; but it has no conception of ex- 

 panse or surface — no idea of immense distances, and no 

 desire to push forward its excursions. 



The eye of birds, it is worthy of remark, besides being 

 peculiar in structure, is also greatly larger than in most 

 other animals in proportion to the bulk of the head. 

 According to a vety distinguished writer, the ball of the 

 eye in a female eagle was, at its greatest width, an inch 

 and a half in diameter ; that of the male was three times 

 less ; that of an ibis, six times ; of a stork, four times 

 larger. That of a cassowary was four times larger than 

 its cornea, being an inch and a half in diameter, while the 

 cornea was only three lines. The woodcock has very 

 large, prominent eyes, but it cannot support a strong light, 

 and sees best during twilight ; and as Colonel Montagu 

 remarks, its eyes seem to be peculiarly calculated for 

 collecting the faint rays of light in the darkened vales and 

 sequestered woodlands during nocturnal excursions, thus 

 enabling it to avoid trees aud other obstacles. It is 

 probable, indeed, that the proverbial stupidity of the bird 

 arises from this weakness of sight. Like the owl, indeed, 

 its motions are much more agile and lively at nightfall and 

 dawn than at any other time ; and so strong is this pro- 

 pensity to action at the rise or descent of the sun that 

 woodcock when kept in a room are observed to flutter 

 about regularly every morning and evening, while 

 during the day they only trip on the floor without at- 

 tempting to fly. 



The stone-curlew differs from the last-named particu- 

 larly in this, that, though its eyes are similarly prominent, 

 its sight is very acute in the daytime. The prominence of 

 its eyes enables it to see behind as well as before, and it 

 is with difficulty, therefore, that it can be approached. 



