On the Migration of North American Birds. 85 



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ing the hunters and the wolves, and supporting life by picking the 

 bones of the animals which they have left. Or they are composed 

 of those birds that feed on the buds of trees, such as the Grouse, 

 that live on the buds of the birch, (Bctula,) Poplar, (Populus,) and 

 several species of willow, (Salix.) Or those that feed on the seeds 

 of the pine and spruce, (Abies,) as the Crossbills, ( Curvirostra,) 

 and pine Grosbeaks, (Phorhula enucliator,) or they are birds that 

 are able to find subsistence on the seeds of plants that are protruded 

 above the snow, or on the seeds of grass found in the barn yards 

 or haystacks of the farmers, such as a few species of the sparrow. 

 But those immense numbers of birds, that feed on insects and worms 

 all migrate to those countries where they are abundantly supplied with 

 this kind of food. These are the Swallows, (Hirundo,) the night 

 Hawks and the Whippoorvvill, (Caprimulgus,) the Tanagers, the fly 

 catchers, and warblers. To them migration is essential to the sup- 

 port of life. The insects at that season disappear, the earth is bound 

 in frost, or covered over with snow, and all the means of subsistence 

 are removed ; but long ere this these lively tenants of the air, have 

 obeyed the impulse of some mysterious instinct, and have migrated 

 to more congenial climes. To these may be added all the birds 

 that obtain food from the muddy and moist places of the earth, such 

 as the different species of Curlew, (Namenius,) the Snipes, (Sco- 

 lopaxy) and the sand birds, (Triiiga,) as well as those ducks that 

 obtain subsistence from fresh water ponds and rivers ; these finding 

 the swamps, brooks, and shores frozen over, migrate from the north 

 to milder regions where they can procure suitable food. 



Those birds that migrate but partially and spend their winters in 

 the northern states, though in a milder temperature than their places 

 of summer retreat, such as the eagles, hawks, owls, and grouse, are 

 enveloped in a warm thick, and downy plumage, which in most of the 

 species extends even over the legs and toes. Other birds are exposed 

 to the water, as well as the cold, such as some species of wild ducks, 

 (Anas,) gulls, (Larus,) petrels, (Procellaria,) and puffins, (Puffinus.) 

 These, gaining a subsistence from the sea, are not obliged to migrate 

 on account of food. In addition to their warmth of covering, which 

 shelter them from the cold, they are supplied with sacs, containing 

 an oleagenous substance with which they regularly lubricate their 

 feathers, thus rendering them imperious to moisture. Whilst float- 

 ing on the surface of the water, they often draw up their feet be- 

 neath their warm covering of down, and thus every part of the body 



