'TWIXT COLD AND HEAT. 81 



Here we have an instance of the exercise of choice, on 

 the part of a bird, which is full of interest. The wool- 

 len threads being otherwise identical, it was the color 

 only that influenced the choice of the birds : they real- 

 ized that the red or yellow yarns would render the nest 

 conspicuous, although well protected by the foliage of 

 the branch to which it was attached. Why the green 

 threads were not taken I cannot imagine. As a result 

 of this experiment, I anticipated that the orioles would 

 reserve the brightly colored yarns for the lining of the 

 nest, and the gray and green for the exterior. This was 

 a result obtained two years ago, when I tried a similar 

 experiment ; but the use of red yarn as a lining may 

 have been merely accidental. 



Out of mere curiosity, for I could not anticipate what 

 might be the result, I made a few transfers of the eggs 

 of one species into the nest of another bird. The results 

 were not, however, particularly suggestive. I placed 

 the eggs of a catbird in the nest of a song thrush, and 

 vice versa. The eggs of the former are dark green ; of 

 the latter, light blue. No act indicative of recognition 

 of the change was observed. I placed eggs of the song 

 sparrow in the nest of a pee-wee, and vice versa. The 

 fly-catchers rejected the eggs of the sparrow; but the 

 latter accepted the situation, although disturbed by 

 it. Many other changes were made, with similar results ; 

 and I concluded that, unless the eggs were greatly dif- 

 ferent in size and color, about one half would be ac- 

 cepted ; but when a single eg^ was placed in the nest 

 of another bird, it was destroyed in nearly every case. 

 This I found to be true, even when I tested such birds 



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