n the ground without any special
protection. As we rise in the scale of the bird world we find nests
provided for the eggs. These nests become increasingly complex and
specialized, until we reach the oriole's home with its wonderfully
woven mass of fiber, which, in spite of its apparent looseness,
supports well the weight of the mother bird and of her eggs. The
robin, not content with making a woven basket, plasters it with clay,
and makes an absolutely impervious nest.

When we remember that both mammals and birds are the modern
descendants of cold and scaly reptiles of an earlier geological time,
it becomes interesting to compare their clothing. Evidently in the
mammals hairs began to come out between the scales. Gradually the
scales became fewer and the hairs more abundant until finally the
scales have all disappeared, except those that remain as the claws on
the toes. The ancestors of the birds, on the other hand, boldly
transformed their scales into feathers.

Another need for shelter arises in connection with the approach of
winter. This problem of withstanding the cold season is complicated by
the presence of two new factors. First and most directly, the cold
itself is a distinct obstacle to the comfort of many of these
creatures; as a secondary result of this cold, the food of many
animals disappears entirely in winter. Most of our birds meet this
difficulty by changing their base of operations. When the north grows
cold these creatures fly to the south. Some of their migrations cover
enormous stretches of country. Our bobolink, so well known and loved
by all watchers of spring migrations, passes twice a year between the
latitude of New York and Rio Janeiro. One of our most careful students
of bird migration says that the Golden Plover makes, twice each year,
the long journey from the Arctic shores of North America to the plains
of La Plata.

Different fur-covered animals have specialized to meet the winter by
any one of three different methods. They may brave it out, hunting for
their food as best they can all winter long. Such a course is pursued
by the rabbit. Again like the squirrel, they may store large
quantities of food during the summer, and on this provender they may
subsist during winter, remaining for most of the time near their
hiding-places, which, however, they may frequently leave upon warm
days. A third method is less common, but very interesting. The
groundhog or woodchuck is the best-known