Nighthawks
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By the time that you read this months phenology, the spring bird migration will be drawing to a close. One of the later migrants that you will be seeing or hearing throughout the summer is the common nighthawk. These birds, which are a little smaller than a kestrel, are neither hawks nor nocturnal, although commonly seen around dusk. Nighthawks eat mostly insects, which they catch while flying. They lay their eggs directly on the ground or on a flat roof of a building. These birds are often heard before they are seen. Their call has been described as a sharp, electric peent. The males emit a low sounding booming noise when doing a display flight.
To listen to examples of Nighthawk calls, visit allaboutbirds.org.
Also, check out this YouTube video that has a lot of good information and sounds of the nighthawk.