44 POPULAR SCIENCE MONTHLY. 



ment of a substitute for a snowshoe on a non-migratory bird whose 

 habits keep it largely upon the ground, while no such development 

 would be expected on a bird that leaves us in the winter for warmer 

 climes. 



In this connection I would say that while few of our native birds 

 change the color of their plumage as an adaptation to the seasons, 

 our pretty thistle bird, or American goldfinch, undergoes a radical 

 change. In summer he has a bright yellow body with black mark- 

 ings and a black head, while in winter his plumage is all pale brown 

 or sparrow-color, and we often fail to recognize in our somber win- 

 ter resident the brilliant goldfinch of our summer. These little 

 birds are gregarious in the winter, and as they fly in small flocks 

 into the trees by the roadside they are frequently mistaken for 

 sparrows, and in fact are usually called tree sparrows. 



There are few things connected with the study of natural his- 

 tory more interesting than the tendency in animals to develop con- 

 ditions suitable to their environment, and it is surprising to see for 

 how long a time an acquired habit will sometimes survive after its 

 usefulness has ceased. 



The common chimney swallows always build their nests in chim- 

 neys that are unused during their breeding season. They make a 

 semicircular nest of sticks, which they glue to the inside wall of 

 the chimney with a secretion from their mouths. It is interesting 

 to see the swallows gather the sticks for their nests, for they do 

 not alight on the ground, but, while flying, break off dead twigs 

 from trees without stopping in their flight. 



This habit of building in chimneys must have been acquired in 

 a comparatively short time, for there were no chimneys in this 

 country before the arrival of the white man, and for a long time 

 afterward the settler had but one chimney in his house, which must 

 have been used, at least for cooking purposes, in the summer. So 

 perfect is this habit that the swallow looks and acts as though he 

 were made for the chimney; his color is a sooty black, so that he 

 does not tarnish his coat by rubbing against the chimney walls; 

 the feathers of his tail end in hard spikes, that he can use them to 

 prop himself against the wall. I have been interested on a sum- 

 mer evening watching these swallows in hundreds circling around 

 a church chimney in Plattsburg, until finally the birds in the 

 center began to enter the chimney, the circle growing smaller and 

 smaller as they apparently poured down in the vortex of a whirl- 

 pool of swallows. Many birds have acquired a habit of associat- 

 ing with man, and we rarely find them, except during the season 

 of their flight, far away from houses. 



The barn swallows always place their nests under the eaves or 



