They are a pretty bird. I like listening to them. They are fun to watch swooping around grabbing insects to feed their chicks.
I'm betting they are probably building a nest somewhere near by. From the looks of the picture it is probably up under your porch. Just keep a look out for something that looks like a mud cone up around the edges of your porch. You'll probably see them fly to it if they don't see you.
I know they will try to dive bomb you if they have chicks especially when the chicks have left the nest and are hidden in the grass. A couple years ago I was walking around the house and had both parents start diving at my head and while ducking I realized they had two chicks on the ground. I tried to get by quickly and another group attacked.