302 The Bird 



a ptarmigan, while yet in the brown garb of summer, 

 is exposed against a hillside of snow, it becomes very 

 wary. 



It is interesting, in this connection, to observe how a 

 Nighthawk carries out its colour resemblance to a knot 

 or a rough piece of bark, by perchiyg, not crosswise, but 

 lengthwise, along a branch or fallen tree-trunk. 



A volume might easily be written of the various ways 

 in which protective coloration works out among birds, 

 but there is so great a difference of opinion, and indeed 

 so many exceptions to every theory which may be ad- 

 vanced, that it is better, for the most part, to go to Nature 

 without a priori theories, and putting ourselves as nearly 

 as possible in the position of the creatures themselves, 

 to hope for better ability to see with their eyes. And 

 it is right along this line that we most need fresh data 

 and experiments, namely, the actual ability of birds 

 and insects to distinguish shades, colours, forms, and 

 motion, — whether efficient in certain ways or not. We 

 know that man}^ m.en cannot distinguish a scarlet ball 

 lying upon green grass; that is, they are partly colour- 

 blind. If this were the case with certain hawks, a male 

 Scarlet Tanager would be forever safe from them among 

 the green foliage. 



An important fact, which for j^ears had been appar- 

 ent to me, l3ut unexpressed until Mr. Abbott Tha^^er put it 

 into words, is that colours which we would ordinarily term 

 conspicuous are often exactly the opposite when found in the 

 plumage of a bird. Writing of the Motmot in my volurre 

 ''Two Bird-lovers in Mexico," I say: "I have often 



