@NannyB,
Nanny B...
It appears you have a nesting pair of hawks. You must be getting too close to the nest.
They are swooping down on you because they are protecting their young that are still in the nest.....as any good, loving and protective parent would do.
Most birds act like this when they nest in areas where there are people. I've seen swallows, mockingbirds, magpies and even robins act this way!
Unfortunately their nesting areas are being taken over by people...they are running out of good places to nest...hence they sometimes end up nesting near people...
If you kill them, the babies will starve to death. Stay away from the trees where the nest is and wait a bit (a few weeks at most), the young hawks will learn to fly, and the hawks will leave.
Please don't kill them. Just because they aren't "protected" doesn't mean you should kill them when you find them annoying.
We need to learn to coexist peacefully with the other creatures we share the earth with!