Because most birds appear to be creatures of daylight, it seems remarkable that many should select the night for extended travel. Among the many nocturnal migrants are the smaller birds such as rails, flycatchers, orioles, most of the sparrows, the warblers, vireos, thrushes, and shorebirds. It is common to find woods and fields on one day almost barren of bird life and on the following day filled with sparrows, warblers, and thrushes, which indicates the arrival of migrants during the night. Waterfowl hunters sitting in their "blinds" frequently observe the passage of flocks of ducks and geese, but great numbers of these birds also pass through at night; the calls of Canada geese or the conversational gabbling of a flock of ducks are common night sounds in spring and fall in many parts of the country. Observations made with telescopes focused on the full moon have shown processions of birds, and one observer estimated their passage over his area at the rate of 9,000 per hour. This gives some indication of the numbers of birds in the air at night during peaks of migration. At such times radar observations have shown that nocturnal migration begins about an hour after sundown, reaches a peak shortly before midnight, and then gradually tapers off until daybreak. Unless special circuits are installed in radar sets, bird echoes during peak migration periods may cover a radar screen. It has been suggested that small birds migrate by night to avoid their enemies. To a certain extent this may be true because the group includes not only weak fliers, such as the rails, but also the small song and insectivorous birds, such as wrens, small woodland flycatchers, and other species that habitually live more or less in concealment. These birds are probably much safer making their flights under the protecting cloak of darkness. Nevertheless, it must be remembered that night migrants include also the snipe, sandpipers, and plovers. Most shorebirds are usually found in the open and are among the more powerful fliers, as some of them make annual migratory flights over 2,000 miles nonstop across the ocean.