These birds may be Common Nighthawks. I have not seen any Common Nighthawks before so I am not completely sure if that is what these birds are. About fifteen came by last evening at dusk. I was surprised at the sudden appearance of these pigeon-sized, very fast birds that swooped all around the pond area. They were either way up in the air or were racing around the pond so it was hard to take their picture. The Common Nighthawks live all over the United Staes of America but only spend the Spring and Summer here. In Fall, they migrate South all the way down to South America! These are insect eating birds and are especially good at catching flying insects. They also are not really any kind of hawk.
I was amazed though, that all of the other birds and waterfowl left the area quickly when this flock of visiting birds appeared. Even most of the cattle got out of the pond. Strange. Guess they were wary of the new birds that may have been both an annoyance and a competitor. I took the pictures here in the yard on August 25, 2012. Please click on the thumbnail image to see the larger picture. Enjoy. I would appreciate any birders who can let me know what these birds are. Thanks!