'TWIXT COLD AND HEAT. 77 



looked foolish. The sparrow twittered to its mate that 

 it was only fun between them ; the wren whistled 

 " mighty queer," and departed. 



Another series of experiments were as follows: find- 

 ing a nest of the summer warbler in a low alder, the 

 foliage of which was about one third grown, I girdled 

 the supporting growths a few inches below the nest. 

 The leaf-buds withered, and the nest, which under or- 

 dinary circumstances would have been quite concealed 

 from view by the full-grown leaves, was now exposed. 

 The nest was abandoned. 



The next girdling experiment was made on the nest 

 of a white-eyed vireo found attached to a low limb of 

 a small beech. The leaves quickly shrivelled, and the 

 nest, although just finished, was abandoned. 



A second experiment of the same sort was tried, with 

 identical result. 



A nest of the summer warbler was found in a low 

 shrub, containing young birds, and the supporting 

 branches were girdled. The leaves witliered and fell, 

 exposing the nest to full view. The parent birds re- 

 mained and successfully reared their brood. 



In these cases we have evidence of mental operations 

 of a more complicated character than any exhibited by 

 the sparrows. It is evident that, in every case, these 

 birds, in selecting the position for their nests, knew that 

 the growth of the foliage would afford a desirable, if 

 not necessary, protection. Finding that the growth of 

 the foliage had been checked, that the little shelter at 

 first afforded was daily growing less, they foresaw that 

 the nests, under these circumstances, would be too much 



