Night travel is probably best for the majority of birds chiefly from the standpoint of feeding. Digestion is very rapid in birds and yet the stomach of one killed during the day almost always contains food. To replace the energy required for long flight, it is essential that either food be obtained at comparatively short intervals or stores of fat be laid on prior to migration. If the smaller migrants were to make protracted flights by day they would arrive at their destination at nightfall almost exhausted, but since they are entirely daylight feeders, they would be unable to obtain food until the following morning. Unless reserve energy was carried in the form of fat, the inability to feed would delay further flights and result in great exhaustion or possibly even death should their evening arrival coincide with cold or stormy weather. By traveling at night, they can pause at daybreak and devote the entire period of daylight to alternate feeding and resting. This schedule permits complete recuperation and resumption of the journey on a subsequent evening after sufficient energy has been restored. The day migrants include, in addition to some of the ducks and geese, the loons, cranes, gulls, pelicans, hawks, swallows, nighthawks, and swifts. Soaring birds, including broad-winged hawks, storks, and vultures, can only migrate during the day because their mode of flight makes them dependent on up-drafts created by heat from the sun for their long distance travels. On the other hand, swifts and swallows feed entirely on diurnal flying insects. The circling flocks are frequently seen in late summer feeding as they travel while working gradually southward. Formerly, great flocks of red-tailed, Swainson's, and rough-legged hawks could be seen wheeling majestically across the sky in the Plains States. In the East, good flights of broad-winged, Cooper's, and sharp-shinned hawks are still often seen, particularly along the Appalachian ridges.