Thank you, Morris. I agree that it seems likely, given they are seen spending all day along the road, that there is some nesting habitat nearby. Yet they totally disappear from here as their little ditch playground drys up. It's an interesting mystery story more than photographically "exciting", I admit.
I'll confess I was hoping I'd see some comments regarding the cheap Viltrox 2.0 TC I used in two of the exposures. I have read that the 100-400 doesn't do well with them, but on posts on a Nikon thread, particularly of a hummingbird, I've been impressed with the ability to have 800mm or 1200 in DX in a pinch and have it be at least "decent"!
Dave