Just as the first wave of autumn air has moved into Missouri, the nighthawks are drifting southward, bound for a winter in the Tropics. Dependent on flying insects for nourishment, these nocturnal hunters will stay well ahead of the freeze line and won't return to the Midwest until early May. Their smaller cousins, the chimney swifts, are more adventurous, hanging around until mid October and returning by mid April.
Of course, the nighthawks do not know that winter is coming and have never experienced the frosty nights of October. They live in a perpetual summer and their urge to migrate is not a response to the cool, dry air that has now invaded Missouri. Rather, the waning daylight triggers their instinct to drift toward the south and they often do so in large, scattered flocks. Watch for them at dusk on calm evenings, flapping and gliding above the city; their relatively large size, halting flight, white wing patches and sharp "peents" distinguish them from the smaller, fast moving swifts.
