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Page:Popular Science Monthly Volume 57.djvu/54

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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 markings 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 winter 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 history more interesting than the tendency in animals to develop conditions 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 chimneys 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 summer 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 whirlpool of swallows. Many birds have acquired a habit of associating 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