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Breeding season activity, based on detections recorded on more than a million 3. minute Breeding Bird Survey stops, reaches a peak for most species during the hour centered at sunrise or in the following hour. Activity of most species then declines gradually as the morning progresses. When large samples are considered, activity patterns for a given species are quite constant from year to year; but each species has its own characteristic pattern and there is much similarity among members of the same genus. Activity reaches a low point in midday, and may almost cease in some habitats (e. g. deserts); but in deciduous forests, activity of many species continues at a reduced rate. By reducing walking rate or lengthening listening periods, productive censusing of many species could be extended into midday. Winter activity is even more strongly oriented toward the early morning.