A good day birding at Rondeau. Mixed flock of shorebirds, mourning warbler, another pileated, and a common nighthawk.
I spotted it flying after it had been disturbed from its roost and Anne saw it land.
That's about the only way to find one of these.
On summer evenings, keep an eye and an ear out for the male Common Nighthawk’s dramatic “booming” display flight. Flying at a height slightly above the treetops, he abruptly dives for the ground. As he peels out of his dive (sometimes just a few meters from the ground) he flexes his wings downward, and the air rushing across his wingtips makes a deep booming or whooshing sound, as if a race car has just passed by. The dives may be directed at females, territorial intruders, and even people.
source - Cornell Lab of Ornithology