They came from the fog.
Not really. They wandered across the shallow lagoon to where we were standing, and I clicked before the camera had focused,
They were followed by a larger group, all adults, one (just southeast of centre in the above image) with colour bands on one leg, and a blue satellite transmitter on the other (marking says HOO1). The family group seemed intent on mooching from us, but the others, likely migrants, were more stand-offish.
On the way back, crossing Westham Island, we saw another flock of Sandhills, thirteen birds in a muddy farm field, very close to the road. A very craney day.